Nagra PORTABLE ANALOGUE AUDIO TAPE RECORDER, 4.2 Instruction Manual

N A G R A 4.2

PORTABLE ANALOGUE AUDIO

TAPE RECORDER

INSTRUCTION MANUAL

(KSA code No. 20 04 004 151)

Kudelski S.A.
NAGRA Tape Recorder Manufacturer
CH-1033 Cheseaux / SWITZERLAND
phone [phone] Copyright reserved for all countries
telex 459 302 nagr ch February 1991 Edition Printed in Switzerland
telefax (021) 732 01 00

http://www.nagraaudio.com

NAGRA, KUDELSKI, NEOPILOT, NEOPILOTTON

NAGRASTATIC, NAGRAFAX

are registered trade - marks, property of

KUDELSKI S.A.

NAGRA Tape Recorders Manufacture

NAGRA / KUDELSKI certifies that this instrument was thoroughly inspected and tested prior to
leaving our factory and is in accordance with the data given in the accompanying test sheet.

We guarantee the products of our own manufacture against any defect arising from faulty
manufacture for a period of one year from the date of delivery. This guarantee covers the repair of
confirmed defects or, if necessary, the replacement of the faulty parts, excluding all other
indemnities.

All freight costs, as well as customs duty and other possible charges, are at the customer's
expense. Our guarantee remains valid in the event of emergency repairs or modifications being
made by the user. However we reserve the right to invoice the customer for any damage caused
by an unqualified person or a false maneuver by the operator.

We decline any responsibility for any and all damages resulting, directly or indirectly, from the use
of our products.

Other products sold by KUDELSKI S.A. are covered by the guarantee clauses of their respective
manufacturers. We decline any responsibility for damages resulting from the use of these products.

We reserve the right to modify the product, and / or the specifications without notice.

CHAPTER I "INSTRUCTION MANUAL"

TABLE OF CONTENTS

1.1 INTRODUCTION ..............................................................................................................7

1.2 CONTROLS: DESCRIPTION AND USE ........................................................................... 10

FRONT PANEL ........................................................................Error! Bookmark not defined.

1. TAPE / DIRECT SWITCH (LINE AND PHONES) ................................................................... 10

2. TAPE / DIRECT (SNAP SWITCH) ....................................................................................... 10

3. POWER SELECTION SWITCH (EXTERNAL / BATTERIES) ............................................ 10

4. MAIN FUNCTION SELECTOR (SIX POSITION ROTARY)....................................................... 10

5. PINCHWHEEL LIFTER (STOP + TEST ONLY ) ..................................................................... 11

6. LEVEL CONTROL (RIGHT) MIC INPUT 2............................................................................. 11

7. LEVEL CONTROL (LEFT) MIC INPUT 1 .............................................................................. 11

8. REFERENCE OSCILLATOR (PU SH BUTTON) .................................................................... 11

9. LINE & PLAYBACK POTENTIOMETER ..........................................................................11

10. MANUAL/AUTOMATIC SELECTOR.............................................................................. 11

11. LID CATCH ................................................................................................................. 11

12. MODULOMETER MODE SELECTION SWITCH ............................................................11

13. FILTER SWITCH ......................................................................................................... 12

14. MODULOMETER .........................................................................................................13

15. PILOT INDICATOR...................................................................................................... 13

16. SPEED AND POWER INDICATOR ...............................................................................13

17. HEADPHONES OUTPUT .............................................................................................13

18. HEADPHONES VOLUME CONTROL ........................................................................... 13

19. REEL FIXING NUT....................................................................................................... 13

TAPE DECK ........................................................................................................................ 14

20. SPEED AND EQUALIZATION SELECTOR................................................................. 14

21. MOBILE TAPE GUIDE ................................................................................................. 14

22. PINCHROLLER ........................................................................................................... 14

23. REWIND AND FAST FORWARD SWITCH ....................................................................14

24. & 34. TAPE REELS ...................................................................................................... 14

25. & 33. TENSION ROLLERS ......................................................................................... 14

26. ERASE HEAD.............................................................................................................. 15

27. STROBOSCOPE ROLLER........................................................................................... 15

28. RECORDING HEAD.................................................................................................... 15

29. PILOT HEAD ...............................................................................................................15

30. PLAYBACK HEAD ....................................................................................................... 15

31. CAPSTAN SHAFT....................................................................................................... 15

32. PINCH WHEEL AND TAPE GUIDE CONTROL LEVER.................................................. 15

33. TAPE TENSION ROLLER (OR TIMER) (SEE 25) ............................................................15

34. TAKE -UP REEL (SEE 24) ..............................................................................................15

1.3 CONNECTORS .............................................................................................................. 16

36. MIKE 2 INPUT............................................................................................................... 16

37. MIKE 1 INPUT............................................................................................................... 16

38. RX .............................................................................................................................. 16

39. ACC (ACCESSORIES)...................................................................................................... 16

40 MIXER......................................................................................................................... 17

41 LINE INPUT.................................................................................................................. 17

42 VOL ............................................................................................................................. 17

43 MICROPHONE INPUT SELECTOR............................................................................... 17

44. PILOT AND CLAPPER INPUTS .................................................................................... 18

45. LINE OUTPUT .............................................................................................................18

46. GROUND (BANANA SOCKET) .......................................................................................... 18

47. LOUDSPEAKER.......................................................................................................... 18

48. POWER PACK ............................................................................................................ 19

49. FIXTURE FOR CARRYING STRAP/HANDLE ................................................................ 19

50. CASE FIXING SCREW................................................................................................. 19

51. PLATE SHOWING RECORDING AND PLAYBACK EQUALIZATION. ............................. 19

2.1. POWER SUPPLY .......................................................................................................... 20

DANGER OF REVERSED POLARIZATION........................................................................ 20

MEASURING BATTERY CON DITION AND POWER SUPPLY VOLTAGE ............................20

BATTERY RESERVE .....................................................................................................20

VOLT / CELL ................................................................................................................. 21

MEASURING THE MOTOR CURRENT.............................................................................. 21

"SPEED & POWER" INDICATOR ....................................................................................... 21

EXTERNAL POWER SUPPLY.......................................................................................... 21

3.0 OPERATION .................................................................................................................. 22

3.2 TAPE SPEED AND STANDARD SELECTION ............................................................... 22

2.3 LOADING A TAPE ON THE RECORDER...................................................................... 22

RECORDING .................................................................................................................... 23

RECORDING WITH MICROPHONES .................................................................................23

RECORDING A LINE SIGNAL............................................................................................ 23

FAST FORWARD / REWIND............................................................................................. 23

PLAYING BACK A RECORDED TAPE ............................................................................... 24

WORKING WITH HEADPHONES .......................................................................................24

2.8 PRECAUTIONS ........................................................................................................... 24

4.1. DIRECT AND TAPE CHAINS.......................................................................................... 25

GENERAL......................................................................................................................... 25

AUDIO INPUTS ................................................................................................................. 25

MANUAL LEVEL CONTROL.............................................................................................. 25

LIMITER........................................................................................................................... 25

AUTOMATIC LEVEL CONTROL (ALC)............................................................................... 26

MEASUREMENT OF SIGNAL LEVEL................................................................................. 26

5.0 PILOT............................................................................................................................ 27

INTRODUCTION ............................................................................................................... 27

RECORDING A PILOT SIGNAL. ........................................................................................ 27

RECORDING THE INTERNAL CRYSTAL ...........................................................................27

RECORDING AN EXTERNAL PILOT SIGNAL. ....................................................................27

SYNCHRONIZING A RECORDED TAPE............................................................................ 28

FREQUENCY METER (OPTIONAL ACCESSORY QFM)..................................................... 28

QUARTZ CRYSTAL PILOT GENERATOR (OPTIONAL ACCESSORY QGX-3)..................... 28

PILOT INDICATOR............................................................................................................ 28

INTERNAL SYNCHRONIZER (OPTIONAL ACCESSORY QSLI) .......................................... 29

SPEED VARIER QSV-2 ..................................................................................................... 29

USE OF SPEED VARIER WHILST FILMING ON PLAYBACK .............................................. 30

RECORDING OF FACSIMILE AND SIMILAR SIGNALS....................................................... 30

PILOT PLAYBACK USING A NAGRA 4.2 L NOT EQUIPPED WITH QSLI SYNCHRONIZER. 30

PILOT PLAYBACK MADE BY NAGRA 4.2 L FITTED WITH QSLI SYNCHRONIZER .............30

PILOT CONNECTORS ...................................................................................................... 31

6.0 BASIC THEORY ............................................................................................................. 32

CONTROL OF THE INPUT SENSITIVITY (MODULATION),DYNAMIC RANGE, SIGNAL-TO-

NOISE RATIO, DECIBELS ................................................................................................. 32

COMPRESSION OF THE DYNAMIC RANGE ..................................................................... 32

WHEN SHOULD COMPRESSION BE DO NE?....................................................................33

5.3. INTERFERENCE ........................................................................................................ 34

ELECTROSTATIC INDUCTION ..........................................................................................34

ACTION TO BE TAKEN AGAINST ELECTROSTATIC INDUCTION ..................................... 34

MAGNETIC INDUCTION ....................................................................................................35

CABLE PREAMPLIFIERS .................................................................................................. 35

5.4. VOLTAGE OR CURRENT FEED................................................................................. 35

FILTERING PREAMPLIFIERS............................................................................................ 35

MAGNETIC HEADS ...........................................................................................................36

ADJUSTEMENT OF HEAD AZIMUTH ................................................................................ 36

Theory .......................................................................................................................... 36

Variation of the High Frequency Level with Azimuth Error .................................................36

Secondary Maxima ........................................................................................................ 37

Orientation of the Heads on the Nagra 4.2 ....................................................................... 37

Bias .............................................................................................................................. 37

Effect of Bias Signal Amplitude on the Recording .............................................................37

High Frequency Pre-emphasis ........................................................................................38

Relation between Pre-emphasis and Bias....................................................................... 38

Practical Conclusions ..................................................................................................... 39

DETERMINATION OF THE BIAS LEVEL............................................................................ 39

Tape Characteristics ......................................................................................................39

General Procedure......................................................................................................... 39

Variation of k ................................................................................................................. 39

7.0 CALIBRATION AND CARE.............................................................................................. 40

HEIGHT OF THE NEOPILOT HEAD ...................................................................................40

AZIMUTH ADJUSTMENT OF THE PLAYBACK HEAD......................................................... 40

AZIMUTH ADJUSTMENT OF THE RECORDING HEAD. ..................................................... 40

6.2. MAINTENANCE OF THE MOTOR COMMUTATOR...................................................... 41

Remedy for Motor Noise................................................................................................. 41

Metalization of the Commutator .......................................................................................41

Cleaning of the Commutator........................................................................................... 41

6.3. LUBRICATION............................................................................................................ 42

8.0 MICROPHONES............................................................................................................. 43

INTRODUCTION ............................................................................................................... 43

5.2. THE MICROPHONES ................................................................................................. 43

MICROPHONE CHARACTERISTICS ................................................................................. 43

Sensitivity ......................................................................................................................43

Frequency Response..................................................................................................... 43

Coloration. Transient Reproduction. Reverberation .......................................................... 43

Use at High Sound Levels .............................................................................................. 44

Signal-to-noise Ratio...................................................................................................... 44

Directional Characteristics.............................................................................................. 44

SECONDARY CHARACTERISTICS RELATED TO DIRECTIONAL CHARACTERISTICS .............................45

PRACTICAL ADVICE ON THE CHOICE OF THE MICROPHONES...................................... 45

Omni-directional Microphones (pressure) ........................................................................ 45

Bi directional Microphones (velocity) ............................................................................... 45

Switchable Microphones................................................................................................. 46

Choice between Condenser or Dynamic Microphones ...................................................... 46

5.6. MAXIMUM GAIN OF THE RECORDING CHAIN OR SENSITIVITY OF THE

MICROPHONE INPUTS .................................................................................................... 46

Nagra 4.2 Preamplifiers .................................................................................................. 46

Changing the Plug-in Preamplifiers ................................................................................. 47

Plug-in Preamplifiers ...................................................................................................... 47

"STATIC 5" Code: QPM-3-5............................................................................................ 47

"HIGH LEVEL LINE" Code: QPM-6 ................................................................................. 47

"UNIVERSAL" Code: QPAUT & QPUT ............................................................................ 47

SPECIAL PLUG -IN PREAMPLIFIERS ................................................................................48

Filtering Versions of the QPSE ........................................................................................48

Cable Preamplifiers........................................................................................................ 48

LOW FREQUENCY ROLL -OFF ATTENUATORS ................................................................48

Why Filter? .................................................................................................................... 48

When should Filtering be done?...................................................................................... 49

Conclusion .................................................................................................................... 49

METERING .......................................................................................................................... 50

MODULOMETER OR V.U. METER.................................................................................... 50

MODULOMETER .............................................................................................................. 50

V.U. METER...................................................................................................................... 50

CONCLUSIONS ................................................................................................................ 51

REMARKS ON THE CALIBRATION ................................................................................... 51

9.0 SPECIFICATIONS .......................................................................................................... 52

DIMENSIONS AND WEIGHT............................................................................................. 52

POWER SUPPLY ............................................................................................................. 52

TAPE TRANSPORT ..........................................................................................................53

WOW AND FLUTTER ........................................................................................................53

AMPLIFIER CHAIN............................................................................................................ 53

MAGNETIC TAPE ............................................................................................................. 53

AUTOMATIC LEVEL CONTROL ........................................................................................ 53

FILTERS ........................................................................................................................... 54

REFERENCE GENERATOR .............................................................................................. 54

OUTPUTS......................................................................................................................... 54

BUILT-IN LOUDSPEAKER .................................................................................................54

OPERATING CONDITIONS ............................................................................................... 54

MODULOMETER .............................................................................................................. 55

INPUTS ............................................................................................................................ 56

1.1 INTRODUCTION

The NAGRA 4.2 was introduced originally in 1971. It is a portable 6.35mm (1/4") mono analogue
audio tape recorder designed for high quality recording having radio, cinema and television
applications.

Many mechanical and electronic modifications have been made to the machine since its release, to
adapt it according to modern day requirements. Despite all these modifications, the machine
remains remarkably similar to the original.

The Nagra 4.2 can be delivered in two different versions both of which are available in either NAB
or CCIR equalization. These versions are as follows:

NQ-LSP Non pilot
NQS-L Pilot

Each version has three speeds: 38 cm/s, 19 cm/s and 9.5 cm/s (15, 7½ and 3 3/4 ips) with the
following standards: NAB and CCIR.

The Nagra 4.2 is a mono recorder recording full track audio on 6.35mm tape, and the Neopilot
synchronization system.

The audio inputs may be used with either the two internal microphone pre-amplifiers (switchable
between Dynamic, T power and Phantom power depending on the microphone pre-amplifier which
is fitted) or as a line input, via the QCE cable.

The NAGRA 4.2 also contains a switchable limiter, a built-in loudspeaker, and an internal reference
generator for line up, and calibration purposes.

Optionally the machine may be fitted with the NEOPILOT pilot option.
The machine may also be powered from either an external supply ATN -3 or internal batteries.
The 4.2 may also be used with the QGB 10" reel adaptor, to allow the use of larger reels for longer

recording and playback.

1.2 CONTROLS: DESCRIPTION AND USE

FRONT PANEL

1. TAPE / DIRECT SWITCH (line and phones)

When in "TAPE" position, the signal is reproduced directly from the tape.
When in "DIRECT" position, there are two possibilities:

A. When recording, the signal is available before arriving on the tape.
B. When playing back, the signal may be adjusted by means of the level control and

corrected by filter switch (13).

2. TAPE / DIRECT (snap switch)

This switch affects the meter in the same way that the previous switch affects the output. Thus
when it is held to the left, the meter will display the "OFF TAPE" signal whereas normally it displays
the "DIRECT" (EE) signal.

3. POWER SELECTION SWITCH (EXTERNAL / BATTERIES)

The NAGRA 4.2 may be powered by either internal batteries or by an external source which may be
selected using this switch. See also the "POWER SUPPLY" section of this manual.

4. MAIN FUNCTION SELECTOR (six position rotary)

STOP Stops the machine completely from any function, and will slightly move the

pinch wheel away from the capstan to prevent a "flat" being caused on the
pinch roller. In this mode no circ uits are powered.

TEST Will power all circuits and allow level adjustment by means of level controls

(6), (7) and (9). In this mode the motor is not powered. All indications of the
modulometer will be of the DIRECT input, irrespective of the position of tape
/ direct switch (1).

RECORD Is the first of the two RECORD positions and corresponds to RECORD

WITH LIMITER where the recording level is limited to +4 dB. This level
remains constant when the input level is between +4 dB and +10 dB. Thus in
this position tape saturation cannot occur and distortion is avoided.

RECORD The limiter is inactivated in this position so(no that recordings that should be

saturated can be limiter) made. (e.g. gun shots or explosions).

PLAYBACK Is the first of the two playbac k possibilities and corresponds to playback of

the tape to the headphones and line output only.

PLAYBACK This position is exactly as above, only it allows (with monitoring via the

internal loudspeaker at the same speaker) time. This is also the only posit ion
of the main function selector that permits the FAST FORWARD function to
be performed.

5. PINCHWHEEL LIFTER (stop + test only)

6. LEVEL CONTROL (right) mic input 2

7. LEVEL CONTROL (left) mic input 1

These are the main level controls for the two microphone inputs.

8. REFERENCE OSCILLATOR (push button)

On the lower edge of the front panel, between the line and playback potentiometer and the mic 2
potentiometer, there is the reference generator push button. When this button is pressed, a
composite 1.1 kHz signal with a 10 kHz 9th harmonic at a level of approximately -8 dB is injected
into the "DIRECT" chain of the recorder.
The modulometer will show -8 dB. It is useful to record a short burst of this signal at the beginning
of each reel of tape so as to enable the level of the playback chain to be accurately calibrated
before the real recording is made. This also permits adjustment of the record head azimuth in the
field without test equipment. At this point the subject of print -through should be mentioned. After a
certain period of time, a recording may be copied (at reduced level) onto adjacent turns of a tape on
a reel. This produces a perceptible echo during the silences preceding or following a strong sound.
It is thus recommended to leave a pause of two or three turns of tape after recording the "REF"
signal.

9. LINE & PLAYBACK POTENTIOMETER

This potentiometer is used to adjust the line input level when using the machine to record a signal
from the line input (41).

10. MANUAL/AUTOMATIC SELECTOR

This switch allows selection of the sensitivity adjustment of the microphone inputs. In the MANUAL
position the sensitivity is adjusted by means of the potentiometers (6) and (7). In the AUTOMATIC
position 1 this gives ALC (automatic level control) to mic input 1 only and for both mic inputs in the
position 2.

11. LID CATCH

12. MODULOMETER MODE SELECTION SWITCH

This is an eleven position rotary switch allowing different information to be displayed on the
modulometer.
Each position is described below:

X Position not used.
RX Indicates the level of the RF signal picked up by the antenna of the QRR

receiver. (see note)

SYNCH This indicates the phase shift between the pilot playback signal from the tape

and the reference signal. Synchronism is correct when the needle is
stationary.

PILOT PLAYBACK This indicates the level of the pilot signal played back from the tape.
PILOT FREQ This indicates on the +4 to -4% scale of the modulometer, the frequency

deviation as determined by the QFM frequency meter circuit (if fitted),
between the pilot signal being recorded or played back and the 50/60 Hz
reference.

LEVEL The modulometer will indicate the level of the direct or the recorded signal

on the decibel scale.

BATT. RESERVE Indicates on the lower scale, the bold line shows the supply voltage reserve;

the lower limit at the extreme left of the bold line represents 11 V.

VOLT/CELL This is a battery check indicating on the V/CELL scale of the meter and

indicates the Volts per cell of the batteries.

COMPRESSION Compression reading in decibels on the ALC compression scale when

switch (10) is in the AUTOMATIC position.

MOT This indicates the motor current. Maximum deviation = 250 mA.
BIAS This indicates the record bias level on the V/CELL scale.
NOTE : The QRT / QRR radio transmitter and receiver accessories are no longer manufactured.

13. FILTER SWITCH

This is a six position rotary switch, allowing different filter possibilities to be switched in or out.

LFA 2 Low frequency attenuation, -8 dB at 50 Hz.
LFA 1 Low frequency attenuation, -4 dB at 50 Hz.
FLAT The machine has a linear response.
HP 1 High pass filter, -10 dB at 50 Hz.
HP1+LFA1 Combination of high pass and low frequency attenuation, -14 dB at 50 Hz

and -3 dB at 400 Hz.

HP2 High pass filter, -20 dB at 50 Hz.

14. MODULOMETER

This meter is the visual indication of many functions and levels of the machine. The modulometer
displays information according to the position of mode selector switch (12).

The modulometer has 4 scales:

1. Recording leve l in dB

2. Frequency deviation in %

3. Battery voltage (volts / cell)

4. Compression

15. PILOT INDICATOR

This rotary "SASS" type indicator shows a white segment when the frequency (if the machine is
fitted with the pilot system) of the pilot signal are correct.

NOTE: This only indicates the presence of a correct signal being fed to, or coming from the head,

and does not guarantee correct recording of the signal. This should be checked by
switching the modulometer to PILOT playback (this does not function in the RECORD
mode).

16. SPEED AND POWER INDICATOR

This rotary "SASS" type indicator gives a quick visual indication that the machine is functioning
correctly and will indicate a white segment when this is the case. It will turn black whenever any of
the following conditions occur:

a.) The power supply voltage (batteries or external) becomes insufficient for correct

operation of the machine.

b.) The motor current reaches its maximum limit, in this case voltage and speed stabilizer

circuit A22 requires the motor to run faster, but this is not possible because the automatic
current limiter circuit has been activated. (If this occurs during normal operation, then
contact your nearest NAGRA agent.)

c.) WOW & FLUTTER is out of tolerance. (Contact NAGRA agent).

Thus, when a white segment is indicated, the operator can be absolutely sure that the power supply
is sufficient, that the motor current is correct, and that the tape speed is within tolerance.

17. HEADPHONES OUTPUT

This 1/4" jack type socket (type 297) is the headphones output socket accepting headphones with
an impedance of anything from 50 Ohm to 600 Ohm. (Optimum value is 200 Ohm).

18. HEADPHONES VOLUME CONTROL

This small potentiometer is adjustable using a screwdriver and adjusts the level fed to headphones
output connector (17).
Position 1 is the minimum and position 6 is the maximum.

19. REEL FIXING NUT

TAPE DECK

20. SPEED AND EQUALIZATION SELECTOR

This is a six position rotary switch permitting the selection of the speed and equalization of the 4.2 in
both record and playback.

Possible settings are:
3 3/4 ips (9.525 cm/s)

7½ ips (19.05 cm/s)
15 ips (38.10 cm/s)

For each of these speed selections there are two possible positions labeled I (STD) and II (LN)
these correspond to different tape types.

For best quality recordings the 15 ips speed is recommended.
For normal recordings, the 7½ ips speed is available. The 3 3/4 ips speed is available for those
cases where the length of recording time of the tape is more critical than the actual quality of the
recording.

21. MOBILE TAPE GUIDE

22. PINCHROLLER

23. REWIND AND FAST FORWARD SWITCH

REWIND is possible with main selector (4) in any position other than STOP, assuming

pinch roller lever (32) is in the fully open position.

FAST FORWARD is possible only with main function selector (4) in the playback (with

loudspeaker) position and pinch roller lever (32) fully engaged.

The central position of this switch is OFF and this is the position that the switch should be in
whenever the machine is not required to spool. Keeping it in this position will prevent accidental
spooling of the tape when opening the pinch roller gate or playing back a recorded tape through the
internal loudspeaker.

24. & 34. TAPE REELS

The 4.2 can be used with reels up to a maximum diameter of 5" (127 mm) with the plexi-glass lid
closed, or up to 7" (178 mm) with the lid open. However, if the QSET option is fitted to the machine
the 7" (178 mm) reels may be used with the lid closed.
If it is necessary to use reels of up to 10" (254 mm), then the QGB large reel adapter may be used.
See Accessories.

25. & 33. TENSION ROLLERS

These two rollers keep the tape tension constant and ensure correct tape handling and positioning.
During normal use neither of these two rollers should be at either end of its travel. If this is the case
refer to the MECHANICAL CALIBRATION section of the service manual.

The two rollers can be replaced by either the QTIM or QLEN tape measuring rollers. The QTIM is
supplied in the place of the take-up reel tension roller as standard equipment. QLEN instead of
QTIM is optional. (To be stated when ordering).

26. ERASE HEAD

This is a full track erase head.

27. STROBOSCOPE ROLLER

This roller comes in two versions: 50 Hz (CCIR machines) and 60 Hz (NA B machines). Using this
roller, it is possible to check that the machine is running at the correct speed, either in record or
playback. This works at all speeds and uses the stroboscopic effect whenever a mains powered
lamp is shone upon it. When at the correct speed, the bars on the roller should appear stationary.

28. RECORDING HEAD

Audio recording head.

29. PILOT HEAD

Neopilot head used for both recording and playback of pilot signals.

30. PLAYBACK HEAD

Audio playback head.

31. CAPSTAN SHAFT

Tape main drive.

32. PINCH WHEEL AND TAPE GUIDE CONTROL LEVER

This lever engages and disengages the tape from the heads and motor capstan shaft. It also moves
the stroboscope roller and mobile tape guide in and out, to allow easy loading of the tape.

When it is in the open position, rapid rewinding is possible. (This lever should never be left in the
open position for long periods of time as this may cause a "FLAT" on the capstan shaft "O" ring).

33. TAPE TENSION ROLLER (OR TIMER) (see 25)

34. TAKE-UP REEL (see 24)

Positions 36 To 49 see CONNECTORS

1.3 CONNECTORS

36. MIKE 2 input

1 = Input signal Ground
2+3 = Balanced signal Input

37. MIKE 1 input

Identical to No 36 above.
NOTE: The microphone inputs are convertible into symmetrical and floating line inputs by

installing, in place of the microphone preamplifiers, preamplifiers type QPM-6 and using
the corresponding potentiometer to control the input level.

38. RX Antenna input for QRR receiver.

39. ACC (accessories)

1. No connection.

2. Ground

3. Line input, current drive. Minimum source
impedance 47 K Ohm. Current for obtaining
0 dB at maximum sensitivity = 3.73µA.

4. Tape speed correction signal input.

5. No connection.

6. -10 V stabilized voltage.

40 MIXER

For connection to external mixing console. (connector type: T 3478 corresponding plug T 3475/1).

1. Input with fixed sensitivity, 560 mV to obtain 0 dB, input
impedance 9 k Ohm. (2.5 Vpp to obtain +4 dB)

2. -10 V stabilized voltage, Maximum current 50 mA. Noise level <
5 V rms.

3. Direct amplifier output, minimum load impedance 10 k Ohm,
output voltage 560 mV at 0 dB. This is a monitoring signal to be
fed back to the mixer.

4. Unstabilized negative supply voltage. Available in all positions
of the main function selector. Current drawn should not exceed
2 A as this may blow the internal fuse with internal batteries.

5. Playback amplifier output minimum load impedance 100 k
Ohm, output voltage 560 mV at 0 dB.

6. Motor stop control terminal. (connect to -10 V to stop motor).
Operational in all modes except REWIND. it is not
recommended to use this remote method in REC as this will
magnetize the recording head and reduce performance.

7. Ground (chassis)

41 LINE INPUT

Banana jack line input connector. Input impedance 100 k Ohm, input voltage to obtain 0 db on
maximum sensitivity 370 mV. Maximum voltage, up to 150 V. This is the value supported by the
input resistance, but it is not recommended to exceed 10 V as crosstalk might be produced. Up to
150 V has been foreseen is to allow for connection to a sound distribution system at 100 V nominal.

42 VOL

Loudspeaker volume control.

43 MICROPHONE INPUT SELECTOR

This is a four position microphone input selector:
DYN 200 = Dynamic microphone impedance 200 Ohm 0.2 mV /

bar (2mV/Pa) sensitivity.

+48 = Condenser microphone, 1,5 mV/ìbar (15mV/pa)

sensitivity +48 V phantom powering.

+12 = Condenser microphone, 1.5 mV/ìbar (15mV/pa)

sensitivity +12 V phantom powering.

T = Condenser microphone, 1.5 mV/ìbar (15mV/pa)

sensitivity +12 V T powering.

44. PILOT AND CLAPPER INPUTS

1. Ground

2. CLAPPER: Clapper oscillator control input (control voltage + 4
to 14 V) or switching on of QRR receiver by connecting to
ground.

3. XTAL: Internal crystal pilot generator out, 50/60Hz.

4. PILOT IN: Pilot signal input, impedance 5 k Ohm. Input level

0.5 – 25 V.

45. LINE OUTPUT

The line output of the Nagra 4.2 is on the right-hand side of the recorder. The load impedance
should be equal to or greater than 600 Ohm. When the "Line and Phones" switch is in the position
"Tape", the line output voltage is 4.4 V into 600 Ohm while playing back a tape recorded at 0 dB.
The Nagra 4.2 can record at a level 4 dB higher than this, thus the maximum line output voltage will
be 7 V. Unloaded, these voltages will be 10% greater. The line output uses two 4mm banana
sockets. It is made up of by the secondary of a transformer and is floating. A banana socket
connected to the chassis is available beside the line output sockets.

46. GROUND (banana socket)

47. LOUDSPEAKER

48. POWER PACK

6 pole connector for external power supply and pilot signal output.

1. - BATT: Negative pole of battery compartment.

2. + BATT: Positive pole of battery compartment.

3. PILOT PLAYBACK: Pilot playback output.

4. SPEED CORRECTION: Tape speed correction input.

5. EXTERNAL -12 to -30: Input for external power supply -12
to -30 V negative pole.

6. -10 R: -10 V stabilized voltage output during record, I max
100 mA

49. FIXTURE FOR CARRYING STR AP/HANDLE

50. CASE FIXING SCREW

51. PLATE SHOWING RECORDING AND PLAYBACK EQUALIZATION.

2.1. POWER SUPPLY

All models of the NAGRA 4.2 may be powered either by an external power supply (ATN-3) or
alternatively by internal batteries. The 4.2 will accept voltages ranging from -11 V to -30 V with
peaks of up to -35 V. The batteries are placed in the bottom of the machine and the polarity is
marked inside the battery compartment. Turning the two fasteners with a screwdriver or a small coin
opens it. All the batteries MUST be orientated in the same direction as indicated on the base of the
battery compartment.

The NAGRA 4.2 houses twelve "D" type 1.5 V cells having a maximum diameter of 33.5 mm and a
length of between 59.5 and 62.5 mm. It is important to remember that corrosive material can leak
out of flat batteries, causing severe damage to the recorder, and therefore it is recommended not to
leave batteries in the machine during periods of storage.

If leakage occurs as a result of leaving flat batteries in the machine, then wash the affected area
with fresh water. The machine will suffer much less from the water than the electrolyte from the
batteries. The external supply is fed into the machine via connector marked POWER PACK (48) on
the right -hand side of the machine. Rechargeable batteries may also be used and can be charged
using the ATN -3C (order no 14376), which includes the charger circuitry.

The 4.2 will function when the power is as low as 12 V (at 15 ips - 38 cm/s) and down to as low as

10.5 V at the lower speeds. (These figures correspond to a machine in perfect condition and

working at room temperature).
When using an external supply, selector switch (3) must be in the "EXTERNAL" position. It must be

in the "BATTERIES" position when internal batteries are in use. It is not necessary to remove the
batteries when working with an external supply (and vice versa).

DANGER OF REVERSED POLARIZATION

A reversed polarized power supply (negative to the chassis) WILL damage the machine. To reduce
the risk of serious damage a diode is placed in parallel with the supply, which will be short -circuited
in the event of, reversed polarization. If such an event occurs with normal "dry cells", they will be
rapidly exhausted and no further damage will occur.

On the other hand, certain accumulators are capable of supplying sufficient current (in excess of 8
amperes) such that the internal wiring of the machine will become hot enough to cause its insulation
to decompose. This will then liberate gas, which causes considerable corrosion. If this happens,
contact your nearest NAGRA agent immediately.

MEASURING BATTERY CONDITION AND POWER SUPPLY VOLTAGE

BATTERY RESERVE

When the Meter Switch is put into the "Batt. Reserve" position the meter will indicate the difference
between the power voltage available and the power, which the Nagra needs. Often the two voltages
will fluctuate. The device will take into consideration the lowest instantaneous voltage and
memorize this. This detail is important, for the average voltage of a power supply can be sufficient
but momentary drops in the voltage can happen and drop lower than the required minimum.
New batteries will give about 18 V whereas the Nagra can be powered by up to 30 V. This explains
why, with new batteries, the needle of the meter will only indicate about 40% full scale, when it is
switched to "Batt. Reserve".

VOLT / CELL

The meter switch in this position works as a simple voltmeter. The centre scale is graduated from 0
to 1.6 V, it indicates 1/12 of the total voltage or the average voltage of 1 cell.
The position Volt/Cell is essentially designed to monitor the voltage of some accumulators, which
would be damaged if they were allowed to discharge below a certain value. This value is 1 V /Cell
for certain manganese dioxide alkaline accumulators.
It is also possible to monitor the external power supply voltage. If when in the position "Batt.
Reserve" position the indication is that the Nagra is not receiving sufficient voltage, but the Volt/Cell
indicates that the power supply voltage is correct, this means that the Nagra requires an abnormally
high voltage. Under these conditions the motor and motor collector should be examined.

MEASURING THE MOTOR CURRENT

The meter will measure the motor current when the meter switch is in the position "Mot". There is no
corresponding scale on the meter but the "Volt/Cell" scale can be used.
Full scale deflection corresponds to a motor current of approximately 250 mA. In "no load" running,
i.e. without tape and with the pinch wheel separated from the capstan (but not in the rewind mode),
the needle should indicate between 0.2 and 0.3 V. If this value is exceeded, see paragraph 6.2.

"SPEED & POWER" INDICATOR

At the lower right-hand side of the front panel there is a rotary indicator marked "SPEED &
POWER". Under normal circumstances a white cross should appear, but it will disappear when:

a.) the power supply voltage becomes insufficient.
b.) the motor current reaches its maximum value. In this case, the speed

stabilizer requires the motor to go faster, but this is not possible as the
current limiter has already reacted. Thus there is a strong probability that the
speed will not be correct.

c.) tachometric WOW is out of tolerance.

In summary, if a white cross appears on the indicator the operator may be sure that the power
supply is sufficient, that the motor turns at the correct speed, and that the tape speed is correct.

EXTERNAL POWER SUPPLY

On the right-hand side of the machine there is a 6 pin Tuchel-type T 3403 connector marked
"POWER PACK". The corresponding plug is the T 3400/1.

The connections are as follows:
pin 1 Battery negative

pin 2 Chassis (positive)
pin 3 Pilot playback output
pin 4 Speed correction signal input
pin 5 Negative external supply
pin 6 -10 V stabilized output.

3.0 OPERATION

On the right -hand side of the front panel is the main function selector, which determines the mode in
which the Nagra works. By putting it into the position "Test", all the circuits are powered, but not the
is motor. If the meter switch, on the upper right -hand side of the modulometer, is switched to the
"BATT. RESERVE" position, the needle of the modulometer indicates that the Nagra is powered. (if
this is not the case see POWER SUPPLY in this manual).
With fresh batteries, the needle will not advance to more than half way up the scale. It only reaches
the extreme right of the scale with an external power supply.

After checking the power supply, put the meter switch to the "LEVEL" position (recording or
modulation level). A microphone can receive sounds of a very variable intensity. The tape must be
recorded as fully as possible, but without the high frequencies passing a level called the "saturation"
level. The modulometer indicates the level of modulation. The needle can deflec t up to the mark
"Max" on the right of the scale, but should not pass this limit. If the needle is deflected less, the
recording will be of a lower level.

The sensitivity, that is to say, the level of recording for a given sound, can be controlled either
manually or automatically. The choice is made by means of the AUTOMATIC/MANUAL switch on
the upper left of the front panel. In the position "MANUAL" the level can be controlled by means of
potentiometers (6) and (7). In the position "AUTOMATIC" an Automat ic Level Controller controls
the level. The modulometer deflects with respect to the incoming signal without reaching the
extreme right -hand end of the scale.

3.2 TAPE SPEED AND STANDARD SELECTION

The NAGRA 4.2 is capable of running at three different speeds, which can be selected by changing
the position of "SPEED AND EQUALIZATION" selector (20) on the top deck of the recorder
between the two spools.

The speeds available are :
3¾ ips (9.525 cm/s)

7½ ips (19.05 cm/s)
15 ips (38.10 cm/s)

Each position of this selector automatically selects the correct equalization of the machine
according to the chosen speed. There are two different positions available for each speed and they
are marked "I" and "II" which represent Standard and Low noise respec tively.

For adjustments of equalization and checking of tape speed refer to the 4.2 SERVICE MANUAL.
NOTE: The NAGRA 4.2 is only equipped with one recording bias oscillator and it is therefore only

possible to bias the recorder for one specific tape type at any one time. However, it is
possible to optimize the equalization in the second position (LN) for a different tape.

2.3 LOADING A TAPE ON THE RECORDER

Select "STOP", then release the tape path from the heads, guides and capstan shaft by pulling
lever (32) forward, until it comes to a complete stop. Remove the spool retaining nuts and place a
reel of tape on the left -hand turntable, with the loose end of the tape coming from the left-hand side
of the spool. Pass the tape around the left -hand guide roller and across in front of the heads, and
around the right -hand guide roller. Attach the end of the tape to the empty spool on the right-hand
turntable. Replace the two spool retaining nuts, and close lever (32) until it reaches its original
position, thus putting the tape into contact with the heads.

NOTE: It is important to lower the head-shield before loading a tape, otherwise the tape may

pass behind it, and thus not be in contact with any of the heads. When the tape has been
loaded and lever (32) has been restored to its original position, the shield may be lifted in
front of the heads.

RECORDING

The NAGRA 4.2 can make a recording using either microphones or a "DIRECT" line input signal.

RECORDING WITH MICROPHONES

When using microphones, connect a microphone to one or both of the two XLR type connectors on
the left -hand side of the recorder. If the QPUT/QPAUT microphone pre-amplifiers are installed in
the recorder, check that the switches corresponding to each of the microphone inputs are in the
correct position corresponding to the type of microphone to be used. The possible selections are T­power, +12 V and +48 V phantom, powering or 200 Ohm dynamic.

The level of the signal coming from the microphones may now be observed by putting the machine
into the "TEST" position and switching modulometer switch (12) to the "LEVEL" position. The gain
may now be adjusted using potentiometers (6) and (7) on the front panel.

Turn the main function selector to either of the two RECORD positions, depending upon whether
the limiter is required or not. Observe the modulometer to see that the levels remain correct
throughout the recording. The modulometer indicates in both RECORD modes the "Direct" signal. It
is possible to show the "off tape" signal during the recording by moving the LINE AND PHONES
snap switch to the left.

Depending on the position of "TAPE / DIRECT" switch (1) it is possible to monitor either the input
signal, or the "off tape" signal on the headphones output during the recording. This is possible
because the NAGRA 4.2 is a three head machine. (Moving this switch will not affect the recording).

RECORDING A LINE SIGNAL

Recording a line input signal rather than a microphone signal is very similar to working with
microphones. Firstly set the microphone potentiometers (6) and (7) to their fully anti-clockwise
positions. (this is to prevent any noise being amplified by the high gain microphone pre-amplifiers,
being recorded on the tape).
Connect the line input signal to the line input connector (41) on the left -hand side of the recorder.
Set the main function selector (4) to the "TEST" position and adjust the level of the incoming signal
on the modulometer by means of the level potentiometer (9) marked "LINE AND PLAYBACK".
Finally switch the main function selector to one of the two "RECORD" positions to start the
recording. When the recording is completed, select "STOP".

FAST FORWARD / REWIND

To rewind a tape put the main function selector in the "STOP" position, and open the pinch wheel
gate by using operating lever (32) then select "TEST" and rewind the tape by means of toggle
switch (23) located on the top left -hand front corner of the top deck.

When the tape is fully rewound always place operating lever (32) back in the fully closed position
(this will prevent a "flat" portion being made on the capstan "O" ring).

To wind a tape fast forward use switch (23) as for rewind. However, it is not necessary to open the
pinch roller gate. The FAST FORWARD position of the toggle switch is only active when the main

function selector is in the PLAYBACK (with loudspeaker) position. This is done to prevent accidental
winding of the tape during RECORDING.

While fast forwarding the tape, the audio on the tape will be heard through the internal loudspeaker.
To avoid damage to the loudspeaker, use the volume control (42) to decrease the level.

PLAYING BACK A RECORDED TAPE

Rewind the tape as explained above, then set main function selector (4) to one of the two possible
"PLAYBACK" positions (either with, or without loudspeaker). The signal from the tape is now
available on line output banana output connectors (45/46) on the right -hand side of the recorder. If
line and phones switch (1) is in the "TAPE" position, the signal is fed directly to the line output s with
no possibility for adjustment. However, if it is in the "DIRECT" position then the output may be
adjusted with the "LINE AND PLAYBACK" potentiometer.
The frequency response may also be modified using "FILTER" switch (13).

WORKING WITH HEADPHONES

If headphones are to be used, they can be plugged into the jack socket (17) on the lower left -hand
front side of the machine.

The level of the headphones may be adjusted using potentiometer (18). In record, the signals can
be monitored either off tape or directly, depending on the position of the line and phones switch.

NOTE: When the machine is in the "TEST" position, the headphones output is always fed with

the "DIRECT" signal.

The headphones output will accept a 1/4" stereo "JACK" connector (type 297) and can be used with
headphones having an impedance from 50 Ohm to 600 Ohm. (Optimum value is 200 Ohm).
During playback, the headphones may be used for monitoring. In the position "Tape" the signal
coming from the tape can be heard. In the position "Direct" a mixing of the signals coming from the
microphones and from the tape can be heard. The mixing of these signals can be controlled by
means of the potentiometers "Mike 1", "Mike 2" and "Line and Playback".
To listen to the recording on an external amplifier/loudspeaker installation, connect it to the Line
Output on the right of the recorder. This output receives the same signal as is transmitted to the
headphones. Loudspeaker signals should not be allowed to feed a microphone. Under these
conditions, the signal passes from the loudspeaker to the microphone, which retransmits it,
producing a howling known as the Larsen effect (acoustic feedback).
To avoid this effect, the "Line and Phones" switch should be placed in the position "Tape", or the
potentiometers "Mike 1" and "Mike 2" turned down.
To playback in the headphones or to an external installation, the position "Playback" of the Main
Function Selector should be chosen. The internal loudspeaker is thus disconnected.

2.8 PRECAUTIONS

The pinch wheel is automatically disengaged in the position "Stop" of the Main Function Selector.
This enables the Nagra to be stored with the Pinch Wheel and Tape Guide Control Lever in the
closed position. If this lever is in the disengaged position, the lid of the recorder can not be closed.

Do not store the recorder with the Main Function Selector in any position other than "Stop", as this
will cause a "flat" to be formed on the pinch roller and this will cause Wow and Flutter problems
during future uses. To avoid the accidental discharge of the batteries, put the "Power" switch into
"External", thereby disconnecting the internal batteries (if installed).
If the recorder has to be stored for a long period of time, remove the batteries, as a corrosive liquid
can leak from discharged batteries.

4.1. DIRECT AND TAPE CHAINS

GENERAL

Signals coming from the microphone(s), line and mixer inputs, once they are amplified, filtered,
controlled and mixed, form the "Direct" signal, which will be recorded on the tape.
The signal played back from the tape gives, after amplification and equalization, the "Tape" signal.
During recording, the "Tape" signal is that which has already been recorded on the tape, and
therefore is not that which is being recorded.
The modulometer measures the level of the "Direct" signal. It is operational even in the absence of
a tape. On the other hand, there will be no "Tape" signal in this case. When the Nagra is in
playback, the level control potentiometer "Line and Playback" is used to adjust the "Tape" signal.
The "Direct" signal is therefore made up not only of the input signals, but also by the playback
signal. This allows for example, the superimposition of a commentary to the signal being played
back form a tape. On the other hand, the "Tape" signal will always be exclusively the playback
signal from the tape.
The line output amplifier, which also feeds the headphones, can be connected either to the "Tape"
signal or to the "Direct" signal, the choice being made by the "Line and Phones" switch on the front
panel. The loudspeaker amplifier is only fed from the "Tape" signal. Acoustic feedback therefore
cannot be produced, even if the microphones are in service, unless, of course, this takes place from
the headphones.
The Line and Phones snap switch allows meter readings of the playback signal while recording. It
always snaps back into the "DIRECT" position.

AUDIO INPUTS

The Nagra 4.2 has 4 inputs:

a.) two microphone inputs
b.) one asymmetrical line input transformable into 3rd microphone input with the

aid of an external preamplifier.

c.) one mixer input at fixed level

MANUAL LEVEL CONTROL

When using manual level control the position of the microphone potentiometers, which are in use,
adjust the input in such a way that the loudest sounds to be rec orded do not exceed the maximum
level. The potentiometers corresponding to the unused inputs should be kept in their anti-clockwise
position.
The active potentiometers can be equally used to give a compression, by increasing the sensitivity
during the soft passages, and vice versa.

LIMITER

The Nagra 4.2 is equipped with a safety limiter, which instantaneously reduces the gain of the
recording amplifier when the signal exceeds the maximum level providing that the RECORD with
limiter position of the Main Function Selector has been selected. This limiting evidently causes
distortion, but it is less objectionable than that caused by saturation of the tape. Normally, the limiter
will only be brought into action when accidents occur. It is possible that, in the middle of a dialogue,
for example, a short but high power sounds exceeding the maximum level can occur. Under these
conditions it is preferable to saturate rather than to limit because the saturation will be practically
unnoticeable due to the short duration of the sound. On the other hand, the limiter requires a certain
recovery time before the normal sensitivity of the chain is re -established. This sensitivity variation

can affect the ambient sound and can be a greater nuisance than saturation by a brief sound. To
avoid this phenomenon, it is necessary to reduce the recovery time of the limiter. Detailed
instructions as to how this can be done will be sent on request. The limiter can be switched off by
setting the Main Function selector to position RECORD - NO LIMITER. This may be advantageous
for certain recordings, e.g. gunshots, explosions, where tape saturation is desired.

AUTOMATIC LEVEL CONTROL (ALC)

The Nagra 4.2 is fitted with an Automatic Level Control. It replaces the manual potentiometer when
the selector switch placed on the left of the meter is on the position "Automatic". In the position "1­Automatic", only microphone No 1 has its sensitivity controlled automatically. Microphone No 2 is
controlled by its respective potentiometer. In "2-Automatic", the ALC circuit controls both
microphone inputs. The operation of the ALC is complex. It is useful to place the meter switch in the
position "Compression" as needle will indicate by how much the sensitivity of the amplifier chain has
been reduced. The extreme left position corresponds to a maximum gain; the extreme right to a
reduction of gain or compression of approximately 30 dB.
When a signal, whose amplitude is sufficient for the maximum recording level to be exceeded,
arrives from the microphone, the Automatic Level Control will instantaneously reduce the gain to
avoid over-modulation (similar to the limiter). If the signal is short, the Automatic Level Control
concludes that it is accidental, and forgets it rapidly, i.e. it returns to its previous sensitivity. On the
other hand, a longer signal is considered useful.

The sensitivity is therefore memorized and maintained. This avoids the increase of background
sound level between words. It can happen, however, that an interfering signal is long. This will
therefore produce a long reduction of sensitivity. To avoid that, the Automatic Level Control has a
circuit of rapid recovery, which enters into action if the level remains less than -10 dB for about 1.5
seconds. Therefore, if a long and loud noise upsets the recording, the recorder can be reset to its
normal sensitivity by keeping quiet for 1½ seconds.
Experience has shown that the Automatic Level Control allows an absolutely automatic recording to
be made for reporting interviews etc. and of a quality, which is difficult to attain with manual control.

MEASUREMENT OF SIGNAL LEVEL

The Nagra 4.2 is equipped with a device for measuring the signal level. Normally, this is a
modulometer, but a v.u. meter is available on special request.
The meter is connected to the "Direct" signal. During recording it measures this level. If the line
amplifier is connected to the "Direct" signal ("Line and Phones" switch in "Direct"), the measurement
will thus be of the signal sent along the line. On the other hand, if the "Line and Phones" switch is in
"Tape", the level sent along the line will be independent of the "Direct" signal and will consequently
not be measured. In any case, the level of this signal cannot be altered. A signal recorded at
nominal level will give a line signal of nominal level.

5.0 PILOT

INTRODUCTION

The NAGRA 4.2 (NQ-L version) is equipped with a Neopilot system. This system developed by
KSA, records a synchronization signal simultaneously with the audio, of 50 Hz (60 Hz in NTSC
countries). Two signals are recorded in phase opposition so as to avoid any interference with the
audio replay chain. The pilot signal serves as a speed reference to ensure that when the tape is
replayed, it is always replayed at the same speed at which it was rec orded. The pilot signal can
either be supplied from an external source (a film camera for example) or can be generated by the
internal crystal generator (QGX-3) if fitted.
If a recording is made with a pilot version of the NAGRA 4.2 it is later possible, during playback, to
lock the speed of the NAGRA by means of the pilot synchronizer (QSLI) to an external reference
signal. This means that providing the "start" point of the recording is known for both the film camera
and the NAGRA then the two can remain in perfect synchronization throughout the tape.
To obtain a film with a synchronous sound it is necessary to keep the image and the sound
continually slaved to one another. The acceptable tolerance is in the region of 40 msec.

RECORDING A PILOT SIGNAL.

A pilot signal can be recorded when recording either a line input signal or with microphones.

RECORDING THE INTERNAL CRYSTAL

For the 4.2 to record its internal crystal the QGX-3 crystal generator must be fitted to the machine.
This is a circuit that is loc ated on the left-hand end of the battery compartment inside the machine.
There are two operating frequencies for this circuit 50 or 60 Hz. Check by means of the switches on
the circuit that tha correct frequency has been selected. Once this is done then switch the main
function selector to the "TEST" position. The pilot indicator (15) on the top right -hand side of the
front panel should show a white segment. If this is not the case then check that the pilot crystal
shorting plug is located in the pilot socket (44).
This shorting plug is like a blank screw in jumper with the letters "XTAL" marked on it. If this is
installed and the rotary indicator does not show a white segment then check that the machine is
correctly powered and that the power selector (3) is in the correct position with respect to the
supplied source. If this is all correct but the indicator remains black then consult your nearest
NAGRA agent.
Once the indicator shows a white segment then the recording is made in exactly the same way as
described for recording the audio, the pilot signal will be recorded automatically. No further
manipulation of the pilot system is needed.

RECORDING AN EXTERNAL PILOT SIGNAL.

Remove the crystal shorting plug in the connector (44) and feed the Pilot input socket (44) by
means of the QCP cable. The other end of the cable must then be connected to the source (either
an ATN-3, camera...). Check that the external pilot signal is present by switching the machine to the
TEST position as above. While making a recording the cable must always be left connected.
Make the recording as above.

SYNCHRONIZING A RECORDED TAPE.

Check that the machine is fitted with the QSLI synchronizer circuit. This circuit is located at the right ­hand end of the battery compartment inside the machine. The circuit faces downwards, and has its
front right corner cut away.
Feed the pilot input connector (44) with the reference signal either from the pilot out socket on the
ATN-3 (for synchronization to mains) or from the machine to which the 4.2 is to be synchronized.
Turn the main function selector to the playback WITH loudspeaker position, and after a short period
(typically 1.5 secs) the pilot indicator (15) should once again show a white segment. Check the level
of the pilot signal from the tape by switching the modulometer switch (12) to the position "PILOT
PLAYBACK" The needle should deflect about half way. If the modulometer selector is switched to
the position "SYNCH" the meter will indicate the deviation between the external pilot reference and
the pilot signal from the tape.

FREQUENCY METER (OPTIONAL ACCESSORY QFM)

This device measures the frequency of the pilot signal. If the meter switch is in the "Pilot Frequency"
position, the meter will indicate the frequency. The scale is from +4% on the left hand side to -4%
on the right. The accuracy is about ±0.1% on the centre of the scale. In addition, the frequency
meter circuit gives a warning if the frequency is more than 5% out from its nominal value. If this is
the case then the rotary "Pilot" indicator turns black. The QFM exists in two version for 50 Hz and
60 Hz (QFM 50 and QFM 60).

QUARTZ CRYSTAL PILOT GENERATOR (OPTIONAL ACCESSORY QGX-3)

This accessory is designed for synchronous filming without a cable between the camera and the
Nagra. It supplies a signal whose frequency is 50 Hz ±0.001%, and is very stable within a wide
temperature range.
The output signal of the generator is connected to pin No 3 of the pilot socket. To record it, it must
be re-introduced into the Nagra by bridging pin No 3 to pin No 4. This is done with the aid of a
dummy plug, which is supplied with the generator, or by a standard plug with the two pins
connected. The solution of using a dummy plug rather than a switch has been adopted in order to
reduce the risk of human error. The QGX-3 is switchable and gives a 50 Hz or 60 Hz signal.

PILOT INDICATOR

This device is found on the upper right of the front panel. It shows a white cross when the Nagra is
in operation and if a pilot signal of sufficient amplitude is provided, and if there is no "Alarm" signal
in the pilot system. The "Alarm" signal will appear and turn the indicator black if the following
conditions occur:

A) if the frequency of the pilot signal is incorrect (on condition that the QFM

frequency meter circuit is installed)

B) if the pilot signal does not reach the pilot head (on condition that the QSLI

synchronizer circuit is installed)

This is indicated in the position "Test" of the main function selector. When the Nagra is in playback,
this indicator will only show a white segment when a pilot signal is being played back from the tape
and another pilot signal is being fed from outside. If one of these two signals is missing, the
indicator will remain back. This is very important when using the QSLI.

INTERNAL SYNCHRONIZER (OPTIONAL ACCESSORY QSLI)

This device has two functions:

A) It measures the amplitude of the playback pilot signal on the tape. With the meter

switch in the position "Pilot Playback" the meter indicates the amplitude. The
normal value should be between 1 and 2 V on the lower middle scale.

B) It can modify the tape speed of the Nagra in order to render the playback pilot

signal synchronous with a pilot signal coming in on the "Pilot" socket on the right
side. For this speed correction to take place, the Nagra must be switched to
"Loudspeaker Playback" and the "Pilot" indicator should show a white cross. The
white cross is only shown if the external pilot reference signal is correct and a pilot
signal is played back from the tape.

When the meter switch (12) is in the "SYNCH" position, the meter is connected to the QSLI, and
shows the difference of phase between the external pilot signal and the playback pilot signal from
the tape. Thus, if the signals do not have exactly the same frequency and phase the needle will
oscillate. This can be seen on "Playback" (without the loudspeaker). One complete oscillation left,
right, left, every 2 seconds corresponds to a speed error of 1%, which can be corrected by the
QSLI.
By putting the main function selector in the (Loudspeaker Playback) position the QLSI is switched
on, and the needle should be stationary. If it continues to oscillate, then the frequency exceeds the
synchronizing capacity of the QSLI. If the Nagra is equipped with frequency meter circuit QFM, and
the needle is stationary and if the pilot indicator shows a white cross, synchronization is practically
certain.
There is one exception, however, if the playback frequency from the tape is grossly incorrect (e.g.
100 Hz instead of 50), the needle will not be able to follow the beat and will remain stationary in the
center of the dial.

If this is suspected, switch to Playback. The needle should oscillate. If need be, upset the tape
speed by blocking the left hand tension roller momentarily. If the needle remains in the center, the
recorded pilot signal is incorrect.
The speed varier QSV-2 is very useful in these cases. In attempting to adjust the speed (on slaved
playback) the QSLI has to adjust itself in order to prevent the speed varier from operating. The
needle of the meter will show this adjustment and will prove that synchronization is correct.

SPEED VARIER QSV -2

This is an external accessory for the Nagra 4.2. It is plugged into the ACC socket (39) on the left
hand side of the recorder. It enables the speed to be varied manually up to ±12%. The QSV-2 is
used for the following applications:

A) To transfer a tape whose pilot signal originated from a camera whose speed was

out of tolerance.

The QSLI synchronizer allows the automatic correction of speed errors up to ±2%.

It is not unknown for cameras to have a speed error greater than this tolerance.
The speed Varier allows the offsetting of the average speed, which will then be
corrected by the Synchronizer in the normal manner. Naturally, under these
conditions, the tone of the sound will be altered, but this is inevitable.

B) Transfer of a tape whose pilot signal is interrupted. A very convenient method of

indicating the start marks (or end of takes) as well as the take identification is by
short interruptions of the pilot signal. During these interruptions, the slaving
between the Nagra 4.2 and the film recorder is suppressed. It is important that the
speed change during the suppression is not brutal, otherwise audible wow will be
heard. To avoid this, it is sufficient to make approximate correction with the aid of

the Speed Varier and to allow the Synchronizer to make a final adjustment to
ensure the slaving.

This can be done as follows:

Method A

1. Play back the tape to be transferred without slaving. When using the QSLI internal
synchronizer, put the Nagra into "Playback" without loudspeaker.

2. Adjust the speed with the aid of the Speed Varier QSV-2 in such a manner that the
playback pilot signal and the mains are approximately synchronized. The needle of the
Nagra meter (switch on "SYNC") will not swing.

3. Rewind the tape and make the transfer in the usual manner. Under these conditions,
the speed correction achieved by the Synchronizer will be very small.

Method B

Make the transfer in the classic manner and adjust the Speed Varier so that the needle
(in the position SYNC) remains at the center of the scale (QSLI). This method is less
precise, but it is sufficient in practice. It should be noted, however, that the
interruptions of the pilot signal happen at the beginning of a sequence, and it is almost
always necessary to make a trial playback, adjust the speed, rewind and then make
the transfer.

USE OF SPEED VARIER WHILST FILMING ON PLAYBACK

Whilst filming on playback, it is possible that the camera may run at an incorrect speed. It will
therefore be necessary to adjust the camera, if possible, to avoid any change in the tone of the final
sound. If this is not possible, correction can be made with the Speed Varier (see above).

RECORDING OF FACSIMILE AND SIMILAR SIGNALS

A Nagra equipped with a Quartz Crystal Pilot Generator and a QSLI Synchronizer can reproduce,
on playback, frequencies with a precision of the order of 0.001%, as any slipping or stretching of the
tape is automatically compensated for. This applies to average frequencies for, inevitably,
mechanical tolerances and longitudinal vibrations of the tape will affect the instantaneous speed
(wow and flutter).
Experience has shown that this precision is more than sufficient for the recording and reproduction
of facsimile signals. Other telemetering applications are, of course possible.

PILOT PLAYBACK USING A NAGRA 4.2 L NOT EQUIPPED WITH QSLI SYNCHRONIZER

Output impedance: 47k Ohm ±20%
Load impedance: from zero to infinity.
Output voltage from tape recorded on Nagra 4.2 L: 330mV ±3 dB.

PILOT PLAYBACK MADE BY NAGRA 4.2 L FITTED WITH QSLI SYNCHRONIZER

Output impedance: 10 k Ohm ±20%
Load impedance: from zero to infinity
Output voltage from tape recorded on Nagra 4.2 L: 0.85 V nominal ±3 dB.

The Nagra 4.2 fitted with a QSLI can be used to measure the playback pilot signal. 0.85 V
corresponds to a meter deflection of 1 V on the scale calibrated from 0 to 2 V and normally used to
measure the voltage per cell of the batteries. 1.7 V corresponds to full scale deflection.

PILOT CONNECTORS

On the Nagra 4.2, the pilot playback signal is to be found on the Power Pack connector (48), which
is a 6 pin Tuchel socket, located on the right -hand side of the recorder.
Pin No 2 is connected to the chassis and the output pilot signal is connected to pin No 3.

6.0 BASIC THEORY

CONTROL OF THE INPUT SENSITIVITY (MODULATION),DYNAMIC RANGE, SIGNAL -TO­NOISE RATIO, DECIBELS

The dynamic range is the ratio between the loudest and softest sound levels. The dynamic range is
large for a symphony orchestra compared to that of an announcer reading a news bulletin.
The signal-to-noise ratio is related to the dynamic range. It is important that the softest sound level
to be recorded is still considerably stronger than the noise. Thus, sound with a large dynamic range
requires a high signal-to-noise ratio. However, this ratio can be practically equal to the dynamic
range in the case where the noise level is close to the threshold of audibility. The subjective
perception of the sound level follows a law, which is approximately logarithmic. It is for this reason
that it is customary to measure sound level as a logarithmic unit. This is the decibel (dB). Each time
the sound power is multiplied by 10, the number of decibels, which that represents is increased by

10. Thus an increase of 100 times equals 20 dB, a 1000 times equals 30 dB etc. It should be
remembered that the power is proportional to the square of the amplitude. The voltage, which a
microphone gives, is proportional to the amplitude. In other words if the voltage increases 10 times,
the power increases 100 times and corresponds to 20 dB.
The decibel is a measure of power ratio and not an absolute value. In taking as a reference, a

sound corresponding to a variation of pressure of 2?10
audibility at 1 kHz) a scale in absolute value will be obtained. A sound of 90 dB will therefore mean
90 dB above 2?10

-4

µbar. The frequency response of the human ear varies with frequency. In order
to compensate for this, the sound level should be measured with filters simulating the variations of
sensitivity of the ear. Thus the decibels become the phon referred to 2?10-4 µbar. The
potentiometer scales of the Nagra 4.2 are graduated in decibels referred to 2?10
these decibels are the same as phons but as the Nagra does not have psophometric filters, it
cannot be considered as a phon meter. With a potentiometer control placed on X dB, a sound of X
dB, captured by a normal microphone (0.2 mV/µbar into 200 ? ) and attacking a normal sensitivity
preamplifier, produces a recording at nominal level. The modulometer will indicate 0 dB.

-4

µbar (value considered as the threshold of

-4

µbar. At 1 kHz,

COMPRESSION OF THE DYNAMIC RANGE

The ideal installation for recording and reproduction should restitute exactly the sound levels, which
have been recorded.
The listener should hear exactly what the microphone heard. The human ear has a dynamic range
of more than 120 dB. The Nagra 4.2 has a signal-to-noise ratio, which is exceptionally high.
However, this ratio can only just reach 70 dB. An amateur tape recorder should, according to the
DIN standard, reach 45 dB. It is clear that the ideal installation is not possible without compressing
the recording and expanding it again on playback.
Listening to a signal with a dynamic range of 120 dB poses some practical problems. The ambient
noise of an apartment or a cinema auditorium is considerably greater than 0 phon. 120 phons
becomes painful to listen to. Therefore, apart from exceptional cases, the listening dynamic range
should be reduced. The choice of this dynamic range and, in consequence, the degree of
compression is one of the essential tasks of the sound engineer.
Classical music discs designed to be listened to on a Hi Fi chain can have a very high dynamic
range. A chamber orchestra can be recorded practically without compression. A symphony
orchestra should be slightly compressed, and this is done with the music score, and requires a good
musical culture.
A transmission designed to be listened to on a Hi Fi chain can have a very high dynamic range.
Practically, everything should be at maximum level. On television, the dynamic range can be fairly
high. At least in those countries where habitation in individual houses is dominant. Apartment blocks
limit the maximum power. In any case, evening transmissions should have a lower dynamic range,
the listening level being considerably reduced, but the pianissimo should still be audible. It is true
that the ambient noise level is also reduced during the evening.
In cinema work, the dynamic range depends upon the public for which the film has been made. In
certain countries the cinemas are very noisy. A comedy film provokes laughter, and this should be
taken into account. The dialogue following a joke should always be at a high level otherwise it will

be drowned in the noise of the auditorium. On the other hand, a suspense scene permits the use of
very low sound levels.
Generally, for dialogue an effect can be obtained not by the absolute level of the sound but by the
contrast. A burst of sound will be much more effective if it is preceded by a passage at a moderate
level. This trick is well known amongst cinema "mixers" -the level is lowered before a forte.

WHEN SHOULD COMPRESSION BE DONE?

A) Recordings indented to be transferred on to a disc. The signal-to-noise ratio of the

modern disc is excellent, but it is important that the noise level of the tape should not
be transferred. If a compression is decided upon, it should be don e at the time of the
original recording, otherwise an increase of the pianissimo will also increase the sound
level of the tape noise. It is difficult to use the complete dynamic range of the recorder
without the risk of exceeding the maximum level when a fortissimo is produced. For
this reason, it is prudent to work simultaneously with two or three tape recorders in
parallel, but whose input sensitivities are varied by a few decibels. The tape which has
been recorded at the highest level, but without the maximum level having been
exceeded, will be the one used for playback. Also, it will be possible to choose, during
editing, certain passages from tape No 1 and others from tape No 2 etc.

B) Recordings intended for radio transmission. The compression should be done at the

time of recording. For reporting ect., the use of an automatic level control can be of
interest. It gives a tendency to always obtain the maximum level, that is, it compresses
to a large degree.

C) Recording intended for radio transmission to be reworked in a studio. In this case, two

methods are possible. The signal-to-noise ratio of the Nagra 4.2 is greater than that of
the radio transmission; therefore it is not essential to use the complete dynamic range
of the Nagra. It is possible, to adjust the sensitivity in such a way that the fortissimo
reaches 0 dB. As the maximum level of the Nagra is +4 dB, there is, therefore, a safety
margin. The compression can be done according to the needs in the studio whilst
working on the final recording.

D) Cinema and Television, where the sound is always edited during the final mixing. The

important thing is to preserve the maximum amount of sound information. The very
large dynamic range of the Nagra 4.2 allows the fortissimo to be recorded at a level
below the maximum, avoiding accidental distortion due to a burst of sound. In many
cases, it may even be desirable to work on automatic level control, but this decision
depends on the circumstances, and those who have to make the decision need no
advice. The problem of microphone and preamplifier noise should be considered. Very
often, the background noise of the recording is not dominated by that of the tape, but
by that of the microphone. In these cases, it is useless to increase the sensitivity
during recording. The general level will be greater but so will that of the noise level.
Nothing is gained in information, but the risk of saturation by a loud sound will be
uselessly increased.

The "point above which it is useless to go" is around the 80 dB mark on the
potentiometer scales. This can be easily verified: replace the microphone by a
resistance equal to the nominal impedance of the microphone to ensure that ambient
noise does not upset the measurement. Record and playback simultaneously ("Line
and Phones" switch on "Tape"), listen with good headphones and increase the
microphone sensitivity. Even with the potentiometer in the extreme left hand position a
noise will be heard. Turn the potentiometer clockwise. Up to 90 dB on the scale, the
noise level will hardly vary. As from 80 dB, the noise of the resistance replacing the
microphone and of the preamplifier becomes dominant. This point varies according to
the quality of the tape used. With a poor tape it can be 78 dB, whereas with an
excellent tape 82 dB. It is also to be supposed that the playback will be made on a
Nagra 4.2 or on a machine with similar performance. If an ordinary machine should be

used, not having a sufficiently quiet playback chain, it may be desirable to increase the
input sensitivity above 80 dB. On the other hand, the problem is completely different if
the tape produced should be used without reworking. In this case, it is necessary to
compress according to the needs even if the noise level of the microphone
considerably exceeds that of the tape. For these applications, there is a special range
of high gain amplifiers available (see section 5).

5.3. INTERFERENCE

To obtain a good signal-to-noise ratio, it is not sufficient to place the microphone well, it is equally
important that no interference can be introduced into the system. An explanation showing how this
interference occurs will be given and also the means to eliminate it.

ELECTROSTATIC INDUCTION

The microphone and the cable, which connects it to the Nagra and the plugs, should all be well
shielded. If these conditions are respected, no electrostatic induction can occur.
However, certain parts of some microphones are grounded by a simple contact, which is not
protected against corrosion. Often the plug shielding is similar, and certain cables have only a
symbolic shielding.
In these cases any electrostatic field can induce interference voltages into the system, in particular if
the Nagra is not grounded but is connected to a camera, which is not interference suppressed and
the entire system is at a voltage above ground. Hence, the ground itself, as seen by a cable, is a
potential source of interference. In other words, interference is introduced at the slightest defect of
the shielding. The induced interference can be at an audio frequency or a high frequency, which
can be detected within the recorder.

ACTION TO BE TAKEN AGAINST ELECTROSTATIC INDUCTION

1. Good shielding. Above all, check the plugs.

2. Avoid the conditions where the Nagra is floating above ground with an int erference
voltage. One possibility is to use a photoelectric coupler between the camera and the
Nagra. Obviously, no trouble can arise if quartz crystal synchronization is used.

3. If, for any reason, it is not possible to follow the advice given, it is possible to reduce
the interference level by:

a) Using shielded input transformers, which attenuate the passage of indirect

interference.

b) Using symmetrical input (with the middle point grounded, which will

attenuate the passage of direct interference.

c) In the most hopeless cases (such as with a radio transmitter close by) add

external filters.

It should be noted that the microphone preamplifiers of the Nagra 4.2 are already fitted with filters,
but their action only begins at around 500 kHz, becaus e they are, above all, designed to reduce
very high frequency interference for which the usual shielding is ineffective.

MAGNETIC INDUCTION

Certain microphones are sensitive to magnetic fields and they should never be placed close to any
motor, or transformer etc. The cables being double and twisted, means that voltages induced
should cancel one another, whether the input is symmetrical or not. It is essential, of course, that
the microphone should be floating, that is to say, that neither of its output wires should be grounded
(except in the case where the shielding should be connected to the shielding of the cable).
The only case where a magnetic induction can be dangerous is where a microphone cable runs
along-side a power cable. The latter radiates a magnetic field, which is not homogeneous, and any
irregularities in the twisting can suffice to induce interference voltages.

CABLE PREAMPLIFIERS

It would seem somewhat illogical to have to take great precautions to transmit a signal as weak as
that given by a microphone when it would be easy to amplify the signal close to the microphone,
and thereby transmit a higher voltage. This can be done with a cable preamplifier. This accessory is
placed close to a dynamic microphone and gives an output voltage similar to that of a condenser
microphone. The power supply requirements are also similar, so that it is possible to interchange a
condenser microphone with a dynamic microphone fitted with a cable preamplifier. Under these
conditions the Nagra should also be fitted with a plug-in preamplifier designed for a condenser
microphone. As the power supply requirements vary according to the type of condenser
microphone, so there exists a corresponding range of cable preamplifiers, to be fed from each type
of preamplifier.

5.4. VOLTAGE OR CURRENT FEED

By altering the negative feedback, it is possible to adjust the input impedance of any preamplifier to
practically any value. If the input impedance is high, the microphone will not supply any current, and
only the voltage will be used to transmit the signal. This is called a voltage feed. If the impedance
seen by the microphone is very low, the voltage at the microphone terminals will remain negligible,
but the microphone will supply a current, which will transmit the signal. This is called a current feed.
A dynamic microphone whose impedance is constant as a function of frequency can be used
indifferently for current of voltage feed. Current feed offers certain advantages: the performance of
the input transformer has much less influence on the overall result, the noise level is minimum when
the input is open etc. This last point ensures that a recording will not be spoilt if an unused channel
is left with the level control open. Therefore, when there is a possible choice, current feed would
seem to be preferable. Unfortunately, microphones with a cardioid characteristic possess an
internal impedance which varies greatly with frequency and they can be used only for voltage feed.
Thus the standard pre-amplifiers for the Nagra 4.2 use the voltage feed method, but current feed
preamplifiers are available for special cases, where desired.

FILTERING PREAMPLIFIERS

In a large number of cases, it is desirable to attenuate very low frequency signals captured by a
microphone. As the human voice contains practically nothing below 50 Hz, a flat frequency
response down to 20 Hz is not only useless, but can be objectionable because low frequency
noises can perturb the recording chain.
The filtering is usually done at the final mixing, but if it is known that there are very low frequencies,
which should be eliminated, it is better to do it within the preamplifier. Several models of plug-in
preamplifier are available for doing this correction.
In the preamplifier code, the figure following the letter Y indicates the attenuation of a signal at 50
Hz in decibels.

MAGNETIC HEADS

There are four tape heads on the NAGRA 4.2, these being ERASE, RECORD, PILOT and
PLAYBACK (see "CONTROLS at the front of this manual for their location).
Contact between the magnetic head and the tape must be perfect. Some tapes leave deposits on
the heads. Fortunately, the deposits are clearly visible. A dirty playback head gives a muffled
sound, lacking high frequencies. If the high frequencies come and go rapidly (one to ten times per
second), the azimuth needs adjusting. A dirty recording head will record at a low level, and the
sound will be distorted. Under the same conditions an erase head will give poor erasing. To remove
the deposit, it is necessary to soft en it with the aid of a solvent. The simplest method is to take
some absorbent cotton or a rag, soaked in alcohol, or even water and to lightly rub. Chlorinated
solvents, such as trichlorethylene, should be used with care, as it is possible they may lightly attack
the resins used in the construction of the heads.

ADJUSTEMENT OF HEAD AZIMUTH

Theory

The recording and the playback of a magnetic tape is a function of gaps in the recording and
playback heads. These gaps should make a certain angle, arbitrary in itself, with the tape, but which
should be the same for recording and for playback. Any angular difference between the recording
and playback heads will produce a loss of level. This phenomenon becomes more important as the
wave length (that is to say the ratio between the tape speed and the recorded signal frequency)
becomes short.
Practically, a faulty azimuth gives muffled recordings without high frequencies. To ensure the
interchangeability of tapes, the azimuth angle has been standardized: the angle between the gap
and the tape should be 90?. Special recorders, whose heads have been optically aligned, have
been constructed in order to produce Standard Tapes whose purpose is to permit the adjustment of
the azimuth on ordinary tape recorders. It is to be noted that if a recorder has been used for
recording with a badly adjusted azimuth, it is perfectly possible to save the recordings: it is sufficient
to adjust the playback head in consequence. This can be done by means of the ear, by orienting
the playback head to obtain the sound, which is richest in high frequencies. This method is evidently
also applicable to tapes, which have been deformed by a faulty spooling, or by climatic conditions. If
the tape is "sabred", or curved the notion of azimuth becomes delicate, and depends upon the
relative positions of the heads and the guides. Parenthetically, it is these problems, which limit the
use of very low speeds, below 7½ ips, because it is difficult to ensure a sufficiently precise azimuth
unless only a narrow track is used. In effect, the error tolerance of the azimuth increases as the
width of the track decreases.
In reducing the width of the track, so is the signal-to-noise ratio reduced. Thus the solution of low
speed and narrow track is, above all, used nowadays for amateur machines.

Variation of the High Frequency Level with Azimuth Error

When the azimuth is very slowly adjusted past the optimum position, the high frequencies are
reduced at first very slowly, then their attenuation is accelerated the further the adjustment is made
from the correct point. A curve, which represents this attenuation as a function of the angle of error,
has a rounded summit, and sides more and more steep.
This is important, because if the azimuth is adjusted simply in look ing for a maximum, it is quite
possible that instead of being at the summit of the curve-that is to say at the optimum point -it could
be at one side or the other. If the errors of the playback head and the recording head are additive,
the tape could be recorded out of tolerance. The recording head is adjusted by referring to the
playback head. Thus the azimuth of the recording head has the sum of the errors: that which is
produced in adjusting the recording head, and the playback head.
It is therefore important that the azimuths should be adjusted as closely as possible to the top of the
curve. This is possible by looking for two points about the maximum, which correspond to a certain
attenuation of the high frequencies, and then adjusting to the midpoint.

Secondary Maxima

If the misalignment of the azimuth is continued at the same time as observing the playback of a high
frequency signal, it can be seen that after having passed by a minimum, the signal will increase
again to pass by another secondary maximum.
If the principal maximum corresponding to the correct angle applies equally to all frequencies, the
secondary maximum applies only to one frequency, which is fixed for the particular conditions. If
this frequency changes, the position of the secondary maximum is displaced. It is clear that the
secondary maximum corresponds to an adjustment which can not be used and which should be
avoided. If it is necessary to adjust the azimuth, it should be done by very small degrees, so that no
risk exists of reaching a secondary maximum. On the other hand, if it is necessary to adjust the
azimuth from scratch, it is better to make the adjustment with a fairly low frequency (1, then 3 kHz)
to obtain an approximate azimuth position. At these frequencies, the secondary maxima are outside
the range for adjustment of the heads.

Orientation of the Heads on the Nagra 4.2

The heads of the Nagra 4.2 are pressed down on a cam. On turning this cam, the azimuth is varied.
The outside of the cam is in the form of a gear wheel m eshed with a pinion, which is visible in front
of each head. The pinion can be turned by means of 2½ mm "Allen" key. The Allen key should be
demagnetized before using it as a magnetized tool can induce a very low frequency into the
playback head, which could upset the adjustment.

Bias

To record, that is to say, to magnetize a magnetic tape, it is necessary to submit it to a magnetic
field, which passes a certain threshold value. Below this value, no permanent magnetization will be
produced. To reach the threshold, and to pass into the linear part of the magnetization curves, the
audio frequency signal is superimposed upon it. The peaks of the high frequency signal always
make an excursion into the linear region. The low frequency signal determines, in effect, to what
point the excursion will be made. This is called high frequency bias. Its amplitude influences notably
the quality of the recording obtained, and the determination of its level should be made precisely.

Effect of Bias Signal Amplitude on the Recording

If a low frequency signal (400 Hz) is applied to a recording head whose bias level is varied, several
effects can be observed. A low level bias signal will give a weak distorted signal on playback. As the
bias level increases, so the level of the signal increases, rapidly. A maximum will then be reached,
after which the signal level will be very slowly reduced. The maximum can be called the "Point of
Maximum Efficiency". It corresponds also to the point where the distortion is the minimum. The fac t
that the signal becomes too great, renders the determination of the optimum point rather difficult. A
high frequency signal (e.g. 10 kHz) will give its maximum level for a bias level noticeably lower and
which corresponds to a point where a low frequency signal would become distorted. This is due to
the fact that the magnetic layer of the tape is not infinitely thin. The point of maximum efficiency for
a low frequency corresponds to an optimum recording throughout the whole of the magnetic layer.
The outside part will in fact be over-biased and, to a certain extent, even partially erased. The
middle of the layer is further away from the heads, hence the loss of high frequencies. It is essential
to remember that in over-biasing, not only is the efficiency of the recording of the high frequencies
diminished, which can be compensated for by an increase in the recording current, but the playback
signal is attenuated, thereby showing saturation of the magnetic tape. On the other hand, an over­bias will lower the noise level of the tape.

High Frequency Pre -emphasis

The signal-to-noise ratio of the magnetic tape is perhaps the least satisfactory of its characteristics.
Great efforts have been made to improve this defect. It is possible to imagine, for example, a tape
recorder, which sends to the recording head a current, which is proportional to the input signal,
independent of the frequency (recording at constant current).
Experience shows that the tape becomes saturated for a given current in the recording head
irrespective of the frequency. At high frequencies the saturation takes on special characteristics.
The harmonics, which the saturation should produce, go out of the range of the spectrum, which the
playback head can reproduce. Therefore, a tape saturated in the high frequencies does not give a
distorted signal. Simply, an increase of the recording current does not produce an increase of the
recorded signal.
In effect, the tape becomes a limiter, which, in addition, alters the sonority of the recording.
A tape recorded under these conditions (constant current) should be played back on a head
followed by an amplifier fitted with frequency response correctors so that the ensemble will be
linear.
It can be seen that with the sounds, which are normally recorded, the level of the high frequencies
is noticeably lower than that of the middle frequencies. To be exact, the peaks of the high
frequencies can have a large amplitude but their duration is very short, and a limiting will pass
unnoticed.
From the idea of emphasizing the high frequencies during recording and to attenuate them during
playback, the noise level of the tape, which is annoying above all in the high frequencies, is
effectively reduced. This is known as pre-emphasis. It is used universally in disc recording and
frequency modulation radio transmission as well as in magnetic recording. This universality is very
important, for if there is a pre-emphasis in any link of a chain, it is useless not to have it in the other
links, because, in any case, the high frequency peaks will be limited in the link which has the
strongest pre-emphasis. On the other hand, the gain in the signal-to-noise ratio is preserved in each
link. As a summary, the recourse to pre-emphasis is universal, as it has been found that the
possible limiting of high frequency peaks is less annoying than the high noise level without pre­emphasis.
How much pre-emphasis can be accepted? The question is complex, for it depends upon the type
of sound to record. The sound spectrum varies with different languages, and it is for this reason that
the standards for pre-emphasis vary from one country to another. For practical reasons, it is not the
pre-emphasis, which has been standardized in the case of magnetic recording, but the playback
chain. The recorder should be adjusted so that a tape produced on it and played back on a
standard playback chain should have a linear response, this is the same as standardizing the pre­emphasis for a given type of tape. There are tapes whose capacity for recording high frequencies is
noticeably higher than that of standard tapes. To record on these tapes, according to the standard,
it is necessary to have a lower pre-emphasis.

Relation between Pre -emphasis and Bias

The American NAB standard at 7½ ips requires a greater pre -emphasis than the European CCIR
standard. In Europe, it is normal to slightly over -bias the tape. This gives a slightly better signal-to­noise ratio, but reduces the recording level of the high frequencies. The final result is practically
identical to that obtained with the NAB standard without over-bias. The stronger pre-emphasis of
the NAB standard gives approximately the same improvement in signal-to-noise ratio and the tapes
become practically saturated at the same high frequency signal level. The NAB standard relies
upon a heavier pre-emphasis and the CCIR on the higher bias level.

Practical Conclusions

The result is:

a) It is possible to modify the pre-emphasis, within certain limits, by adjusting the bias

level but still remaining within the limits of the standards.

b) To record sounds particularly rich in high frequencies, it is possible that the use of

tapes, which permit high recording level of the high frequencies, could give better
results.

c) It is necessary to determine which link in the chain gives the greatest pre -emphasis.

If all links pre-emphasize to the same degree, this will produce the most rational
chain. However, if one link becomes saturated, it is better for this to be the magnetic
tape, for the saturation of the high frequencies does not lead to audible distortion,
which is not the case with a frequency modulation transmitter (or rather, the
corresponding receiver).

DETERMINATION OF THE BIAS LEVEL

Tape Characteristics

The tapes on the American market are very similar to one another from the point of view of the
optimum bias level. This permits the adjustments to be made very close to the point of maximum
efficiency. It would be undesirable to adjust directly on to this point, as an over -biasing is much less
dangerous than an under -biasing. This working point close to the point of maximum efficiency is
very convenient for the NAB standards, as shall be shown.
In Europe there is a greater range of tape characteristics. In over-biasing the ordinary tapes, the
working point remains correct for the tapes, the working point remains correct for the tapes at a high
bias level. This ties in with the CCIR standards and gives good results.

General Procedure

It is necessary to use a reference tape whose characteristics are well known, above all in relation to
other tapes on the market. The normal reference tape is CCIR PER 368 and NAB 3M 808.
It is necessary to determine the bias level, which gives the greatest efficiency. The signal used will
be of fairly low frequency (400 Hz). To locate the peak of the curve more easily, two points, E1 and
E2, should be looked for. Point E1 has an underbias level which gives lowering of the playback level
by 1 dB; E2 is an over-bias level, which gives a lowering of the playback signal by 0.5 dB . The
asymmetry of the form of the curve justifies the difference in the playback levels of E1 and E2. It is
evidently necessary to use a sufficiently regular tape so that variations of the sensitivity should not
be confused with the loss of level due to under and over-biasing.
The maximum efficiency bias level Em will be the geometric mean of E1 and E2. Multiplying E1 by
E2 and taking the square root of the product find this. The working point will be Em?k where k is the
coefficient of over-biasing.

Variation of k

The preceding rules take into account the dispersion of the characteristics of available tapes. If a
recorder is only used with one specific type of tape it is possible to use a value of k, which will be
optimum for the conditions. Values of k from 1 to 1.3 are possible.
A small value of k can be used if the sounds to be recorded are rich in high frequencies, or if the
tape is of a low quality for high frequencies. A value of k above average can be used in the opposite
case. The value 1.2 is acceptable for the CCIR standard, and 1 to 1.1 for the NAB standard (50 ìms
at 7.5"/second).

7.0 CALIBRATION AND CARE

HEIGHT OF THE NEOPILOT HEAD

The middle head of the Nagra 4.2 is used to record and playback the pilot signal. Its azimuth is not
critical, but its height should be correct. The cam of this head does not vary the angle, but only its
height. Before adjusting the azimuth, check and adjust (if need be) this head. Adjust the height so
that the tape is exactly in the middle of the head. The eye is sufficiently accurate for this adjustment.

AZIMUTH ADJUSTMENT OF THE PLAYBACK HEAD.

Playback a Standard Tape at 7½ ips. Place the "Line and Phones" switch in the "Direct" position.
The modulometer will thus indicate the playback level. Check that the microphone potentiometers
are in their extreme anti-clockwise position, and adjust the "Line and Playback" potentiometer to
give a convenient playback level. Standard Tapes are generally recorded at between -10 and -20
dB, so that, in general, it will be necessary to put this potentiometer in the maximum position, or
nearly so, to have a playback level of about -10 dB.
Introduce the key into the pinion of the playback head and find the maximum playback level. After
this, look to left and right for the point s where the signal level is lowered by 1 to 2 dB, and place the
pinion midway between these points.
A correct adjustment corresponds equally to a stable playback. Errors due to "sabring" of the tape
are hardly perceptible at the top of the curve, and only become important on the sides.
Once the playback head has been correctly adjusted for azimuth it should not be touched again.

AZIMUTH ADJUSTMENT OF THE RECORDING HEAD.

Two methods are possible:

1. Standard Method
To use this method, it is necessary to ha ve an audio frequency generator, which can give 1,

3, 10 and 15 kHz and an AF voltmeter or an oscilloscope. It is possible to use a second
Nagra as a voltmeter, by introducing the output signal of the recorder to be adjusted into the
line input of the second one, and using its modulometer as a voltmeter.

Procedure:
a.) Introduce a signal from the generator into the line input of the Nagra, and adjust the level

to -15 dB on the modulometer.

b.) Connect the voltmeter to the line output. The signal to be measured will be approximately

0.8 V R.M.S. The "Line and Phone" switch should be put into the position "Tape".

c.) Thread up a tape and record. The played back signal should be observed on the

voltmeter.

d.) Start with 1 kHz and increase the frequency. When the playback signal starts to be

reduced in level by several dBs, adjust the record head. It should be possible to arrive at
15 kHz, always looking for the midpoint between two of equal attenuation.

2. The "Rectangular 1000" method
Whilst the classic method necessitates bulky instruments, the "Rectangular 1000" method,

equally precise, can be carried out with the aid of the reference generator and good quality
headphones. The ear serves in this case as detector.

In effect, the human ear cannot appreciate the absolute value of a high frequency sinusoidal
signal, but, on the other hand, it can determine the harmonic content of a rectangular signal.
In practice, this becomes a judgment of a tone and to render it as "hard" as possible.

Procedure
a.) Thread a tape onto the Nagra whose playback head has already been adjusted

b.) Press the button REF. GEN.
c.) Record and listen to the signal played back in the headphones ("Line and Phone" switch

on the position "Tape").

d.) Adjust the azimuth of the recording head to obtain a sound as rich in harmonics as

possible. The sound produced in the headphones should be the same in both positions
of the "Line and Phones" switch. Look for the two points on either side of the optimum,
which give a sound equally muffled, and adjust for the midpoint between them.

6.2. MAINTENANCE OF THE MOTOR COLLECTOR

The motor of the Nagra 4.2 has a collector in a special alloy, which is perfectly resistant to
corrosion. This ensures good operation, even under aggressive climates. The motor brushes are of
a graphite silver composition, and their pressure on the collector is ensured by gold plated beryllium
bronze springs.
The brushes wear by friction on the collector and the product of their wear forms a self-lubricating
layer called patina, necessary for the correct operation of the motor. The thickness of this patina
depends on the specific pressure of the brushes. If this is too low, the operation will be noisy
(squeaking). If it is too high, the insulation between the segments of the collector may become
bridged over, resulting in an increase of current consumption.

Remedy for Motor Noise

It should be noted that by motor noise, the normal noise of the motor due to the ball bearings and
the friction of the brushes on the collector segments should be discounted only a squeaking
produced by the vibration of the brushes should be taken into account. Experience has shown that
this can happen when the pressure of a brush falls below 12 grams. The remedy consists of an
increase of the pressure by stretching the brush springs. The normal value is 25 gr ±5 gr.

Metalization of the Collector

During the running in period, it is possible that the brushes have not taken on the exact form of the
collector. Local specific pressure can produce a very thick patina, which can short circuit the
segments of the collector. In the worst case, the “SPEED & POWER” indicator on the front panel
will warn the operator. It is recommended to check occasionally (every 100 hours of use) the no­load current of the motor. To do this, place the meter in the "MOT" position. The meter then
measures the current taken by the motor. There is no special scale for this measurement, but the
lower middle scale graduated 0 to 2 V can be used arbitrarily. With no load, that is to say, without a
tape and with the pinch wheel just separated from the capstan, the needle should indicate between

0.2 and 0.3 V. If the needle indicates higher than 0.4 V, the collector probably requires cleaning.

Cleaning of the Collector

Open the Nagra and pull off the motor shielding (being careful not to deform it). Switch on the motor
and clean the collector by rubbing with a rag or absorbent cotton soaked in a solvent. The insulation
between the segments of the collector should be the same colour as that on the top of the collector.
If the conditions are extremely bad, a very fine abrasive polishing cloth may be used, but it is
essential not to use powdered abrasive, which could possibly cause damage within the motor itself.

6.3. LUBRICATION

In the case of intensive use, it may be necessary, from time to time, to lubricate the ruby pressure
ball on the take-up reel clutch. This ball can be found in the middle of the pulley, which drives the
take-up reel. The best grease to use is an Esso grease, but if the recorder is not to be used at very
low temperatures, any mineral grease can be used.
For other oiling points, use an oil designed for aviation instruments, such as Isoflex PDP65 from
Klüber-Munich, or P10 from the Bendix Aviation Corporation, USA; but once again, for recorders
not to be used in very low temperatures, any good sewing machine oil should be acceptable.

8.0 MICROPHONES

INTRODUCTION

There are several different types of microphone pre-amplifiers available for the NAGRA 4.2, in order
to accommodate almos t all of the different types of microphones presently available. Microphone
technology is not stable, and each year new models are put on to the market. Many of them require
power supplies, which exist in different forms. The output voltages can vary, according to the type,
in the ratio of 1 to 20. This means that it is not advisable to supply a tape recorder with only one
type of microphone pre-amplifier. It is preferable to have interchangeable preamplifiers.

5.2. THE MICROPHONES

A microphone converts acoustic energy into an electrical signal. Numerous physical principles have
been used to obtain this conversion and there are many different types of microphone available:
Condenser, moving coil dynamic, ribbon dynamic, microphones etc. Neither the perfect nor the
universal microphones exist. Each type has its defects and particular qualities, and the choice
depends upon the required effect.

MICROPHONE CHARACTERISTICS

Sensitivity

Placed in a given acoustic field (e.g. µbar R.M.S.), a microphone will give a signal of X mV R.M.S. X
represents the sensitivity or, in effect, its efficiency. To give this value sense, it is also necessary to
state the internal impedance of the microphone and the load impedance.
A classic dynamic microphone may have a sensitivity of 0.2 mV/ìbar from 200 Ohm internal
impedance. A model giving 0.25 mV is considered to be sensitive, whereas a model giving 0.1 mV
is unsuitable for capturing low level sounds.
Condenser microphones always have a preamplifier in the microphone casing, ot herwise their high
impedance would not allow the signal to be transmitted along a cable. At the output of the
preamplifier a typical sensitivity figure is 1-4 mV/µbar with a load impedance of 200 -1000 Ohm. It is
difficult to produce a very low noise preampli fier capable of receiving (without overloading) a signal
given by a condenser microphone placed in a strong acoustic field (100 µbars). For this reason, it is
better to have a special preamplifier for condenser microphones. The use of an attenuator between
a condenser microphone and a preamplifier designed for a dynamic microphone is not
recommended, as the signal-to-noise ratio will be unfavorable.

Frequency Response

The frequency response represents the sensitivity of the microphone as a function of the frequency.
It is possible that the response will be different according to the direction from which the sound
comes. This point is very important and will be dealt with in detail later.
Microphone manufacturers pay careful attentions to the frequency response, and in general, most
of the professional microphones available have a sufficiently good characteristic, at least for sound
arriving along the principal axis.

Coloration. Transient Reproduction. Reverberation

An artificial reverberation chamber may have excellent frequency response, distortion and signal-to­noise characteristics, but it must also modify the signal, which passes it. It adds the reverberation.
This shows that the frequency response, distortion and signal-to-noise ratio are not sufficient to
describe an electro-acoustic device. A moving coil dynamic microphone makes use of resonances

to render its frequency response flat. With continuous sinusoidal signals it functions perfectly, but
when a signal appears suddenly, the resonating device needs a certain time to move. When a
sound disappears suddenly, the resonator continues to produce a signal. The result is that the
transient signal (e.g. a percussive sound) will be colored by the inherent resonance of the
microphones. This explains the difference noted by the ear between microphones with seemingly
identical characteristics.
In general, condenser microphones use resonators only in the extreme high frequencies, where the
coloration phenomenon has little importance. As a result, their fidelity is excellent. Ribbon
microphones can colour the low frequencies. Moving coil dynamic microphones colour to the
greatest extent, this coloration is not always undesirable. They can improve certain voices, and the
experienced engineer will not hesitate to use them under certain conditions. He can also use any
defects in the frequency response for filtering, etc.

Use at High Sound Levels

Ribbon microphones and bi-directional condenser microphones can be damaged by a large air
displacement.
To record an explosion, a moving coil microphone, or better still, an omni-directional condenser
microphone is recommended. A switchable microphone (uni-, bi- or omni -directional) risks the same
damage as an ordinary bi-directional microphone. A microphone can be damaged under these
conditions whether it is being used or not. It is advisable to place bi-directional and cardioid
microphones in sealed boxes if an explosion is likely.
Independent of the risk of damage, it is possible that a microphone will not reproduce well at levels
greater than a certain value, above which the signal would become distorted. In general, moving
coil microphones support the highest levels. Certain condenser microphones are designed so that
an attenuator can be placed between the microphone capsule and the preamplifier.

Signal-to-noise Ratio

The recording of low level sounds can be disturbed by the combination of the microphone and its
preamplifier. The word "combination" is used because the background noise does not come only
from the amplifier. Take the case of a dynamic microphone whose impedance is 200 Ohm. As it

does not have a temperature of absolute zero (- 273? C) the electron movement in this impedance
will produce a noise signal called the thermic noise. The preamplifier adds to the thermic noise its
own inherent noise, but in a recorder such as the Nagra 4.2, the thermic noise is by far the most
important.
The acoustic noise is measured in phons. The phons are decibels whose reference zero has been
fixed by convention at 0.0002 µbars. The measuring device is not linear, but has a frequency
response similar to that of the ear. For low levels, this frequency response is called the ASA "A". It
is possible to find out the equivalent acoustic noise level of a microphone and its preamplifier. Take
for example a microphone of 200 Ohm having a high sensitivity (0.25 mV/µbar). Its noise level
referred to the input will be -126 dBm ASA "A" (the dBm are decibels whose reference zero has
been fixed at 1 mW). Now, 0.0002 µbars is equivalent to 0.005 µV (139 dBm). Therefore the
equivalent noise of this microphone will be 139 - 126 = 13 phons.
This figure is correct only if the impedance of the microphone is 200 Ohm. Often, certain
microphones whose nominal impedance is 200 Ohm have higher impedance's, at least in certain
parts of frequency spectrum. The effect of this is to increase the equivalent noise.
A condenser microphone can also be characterized by an equivalent noise level, thereby making it
possible to compare the performance of these microphones with that of dynamic ones.

Directional Characteristics

Often, when rec ording sound it is desirable to attenuate certain unwanted sounds, such as echoes
coming form the studio walls. Certain microphones have a sensitivity, which varies greatly
according to the direction from which the sounds come. In effect, these combine a pressure
characteristic with a velocity characteristic. Taking into consideration the air pressure at any given
point, a microphone acting as a manometer is called a pressure microphone. The direction from

which the sound comes does not affect the pressure, except at very high frequencies, when the
microphone makes its own shadow.
On the other hand, the velocity of the air molecules can be used in a microphone. The word velocity
implies a combination of speed and direction. A velocity microphone consists of a very light loose
diaphragm, which follows the displacement of the air. It will be sensitive to waves, which strike the
diaphragm perpendicularly whether they come from in front of, or behind it. Waves coming from the
side will have no effect. This is the principle of velocity of bi directional microphones. Such a
microphone eliminates an important fraction of the reverberation and if the source of undesirable
noise is well localized, it can be placed in the dead zone of the microphone.
In combining a pressure microphone with a velocity microphone, a unidirectional, or cardioid
microphone is obtained. The two elements are, of course, mounted in a common casing and
electrically interconnected.

Secondary Characteristics Related to Directional Characteristics

Omni-directional microphones (pressure) are much less affected by the wind than bi-directional
(velocity) or cardioid microphones (because of their velocity element). The light diaphragms of
velocity microphones have a tendency to float in the wind. It has been shown that the velocity
microphones are easily damaged by a sudden air displacement (explosion). The response curve of
an omni-directional microphone is reasonably independent of the direction. However, sounds
coming from behind will have a tendenc y to become muffled. Bi-directional microphones attenuate
the lateral sounds in a relatively uniform manner, but cardioid microphones, and above all, dynamic
ones, can have a very bad frequency response in the null directions. In other words, the attenuation
varies greatly according to the frequency. If a cardioid microphone is used to eliminate undesired
noises, this phenomena is not of great importance. If such a microphone is used to balance the
sound, when a very loud source is placed around the null ar ea of the microphone, it is advisable to
check the results. The internal impedance of omni-directional dynamic microphones is reasonably
constant. They can therefore be used to feed their preamplifier either by voltage or current. On the
other hand, the majority of cardioid microphones have an impedance varying greatly with the
frequency. In this case only a voltage feed is recommended. Directional microphones only function
well if they are sufficiently far from other objects, which can disturb the acoustic field, because an
obstacle disturbs the pressure less than the velocity.

PRACTICAL ADVICE ON THE CHOICE OF THE MICROPHONES

Omni-directional Microphones (pressure)

Robust, with low sensitivity to the wind, reproducing ambient sounds well-their price is lower than
that of directional.
Principal Use: reporting
Special Uses: Lavalier microphone. For this use, special units have been created whose frequency
response compensates for the perturbation of the body, and which takes into account the very low
frequency sounds radiated directly from the chest. Recording music in the open air. Reverberation
is non-existent and there are good microphones available - also very robust of low sensitivity, 0.1
mV/bar, which is acceptable as the sound level is reasonably high in these cases. Recording when
the microphone is placed in the middle of a sound source (e.g. in the middle of an orchestra).

Bi directional Microphones (velocity)

These give a very good attenuation of reverberation, and a good fidelity for sounds coming from the
null direction. They are very sensitive to wind noise, and they accentuate the low frequencies if the
sound source is very close. This phenomenon gives a very "Warm" effect, which is exploited by
certain "charm" singers. Principal uses: music. Dialogue in the case where the microphone is
placed between two speakers. Remarks: Dynamic bi-directional microphones, i.e. ribbon
microphones, are either of very low sensitivity, or very bulky. They radiate a magnetic field, which is
capable of erasing a tape if placed close to it. Condenser microphones have a normal sensitivity.

Switchable Microphones

Certain condenser microphones can function as omni-, bi- or unidirectional by means of a simple
switching.

Choice between Condenser or Dynamic Microphones

Condenser microphones give the best fidelity. In particular their reproduction of transient noises is
excellent, but they cost more and are less robust than the dynamic microphones. They require a
power supply either from the Nagra or from an auxiliary device.
They exist in two types: D.C. polarization and H.F. polarization. The performance and reliability
depend, in the long run, more on the competence of the manufacturer than on the chosen system.
Dynamic microphones are reputed to be more robust, but here again, the technological level of the
manufacturer seems to be more important than the chosen system. The coloration which certain
moving coil microphones give can be used to advantage.

5.6. MAXIMUM GAIN OF THE RECORDING CHAIN OR SENSITIVITY OF THE MICROPHONE

INPUTS

In general, the Nagra 4.2 is used to record the "master tape", that is to say, the original from which
copies are made. In consequence the recording level should, in certain cases, be lower than normal
so that correction can be made during transfer.
In the case where a loud sound is recorded, the noise level is that of the tape itself, the microphone
noise level being lower, due to the reduced gain of the recording chain. In these conditions, it may
be useful to use a high recording level so that the signal-to-noise ratio is as high as possible. In the
case where the sound level is very low, the gain has to be increased to a point where the
microphone/preamplifier combination noise level becomes greater than the tape noise level. Under
these conditions, no advantage is obtained by recording at a high level.
If the sound to be recorded is at a still lower level, it is better to adjust the gain to the point where
the noise from the microphone clearly predominates, and under record the tape. In any case, an
increase of gain will not improve the signal -to-noise ratio, whereas the inconveniences of high level
recording will subsist: distortion and a reduced safety margin in the case of a sudden increase of
sound level.
For these reasons, the sensitivity of the microphone preamplifiers has been limited under normal
conditions to 0.2 mV into 200 Ohm to enable a recording to be made at 0 dB.
However, there exist applications where a Nagra must be used to obtain a tape recorded at nominal
level to avoid having to adjust the playback level. In these cases, it is probably better to use a higher
gain, and there are available increased gain preamplifiers. They are recognized by the figure
following the letter X in the code, which indicates the number of decibels by which the gain has
been increased.

Nagra 4.2 Preamplifiers

There are three types of microphone preamplifiers:

a) plug-in preamplifiers which are fixed inside the Nagra 4.2, but are easily

interchangeable.

b) cable preamplifiers which are placed close to the microphone and which feed a plug-in

preamplifier designed for condenser microphones.

c) auxiliary preamplifiers which transform the line input into a third microphone input.

These accessories are placed between cable connecting input No 3 and the
microphone.

Changing the Plug-in Preamplifiers

These preamplifiers are coupled to the rest of the Nagra by a connector. They are physically held in
place by a small screw accessible from the bottom of the recorder.
On turning the Nagra over, that is, placing it on its cover with the battery compartment upwards, the
screw for preamplifier No1 can be seen, on the left viewed towards the front panel. Immediately to
its right is the screw for preamplifier No 2. Once these screws have been removed, the Nagra can
be opened. To do this, unscrew the two fasteners, which fix the tape deck to the box (on the right ­hand side of the recorder). Turn them in the direction "Open" until the tape deck disengages itself.
Open the Nagra. Remove the preamplifiers, which are immediately behind the meter, simply by
pulling.

Plug-in Preamplifiers

"LINEAR STANDARD -200" Code: QPSE-200-X0Y0 and "STANDARD 50" Code: QPSE-50­X0Y0

These preamplifiers are similar to "STANDARD" type but have no filter incorporated. Their
frequency response is flat from 30 Hz and the attenuation at 20 Hz is in the region of 2 dB.

"HIGH GAIN STANDARD 200" Code: QPSE-200-X6Y3 and "HIGH GAIN STANDARD 50" Code:
QPSE-50-X6Y3

These preamplifiers are similar to the "Standard" type but their gain is double (+6 dB) whereas their
attenuation of the low frequencies is slightly greater (3 dB at 50 Hz). The maximum voltage, which
they can receive, is 20 mV for 200 Ohm and 10 mV for 50 Ohm.
For the application of these preamplifiers see Section 5.6.

"STATIC 5" Code: QPM-3-5

This preamplifier is designed to receive the signal from the Sennheiser condenser microphones
type MKH 105, 405 and 805, Neumann type KM 73, 74, 76 and Schoeps type CMT 40.
At the same time, these microphones are powered from the Nagra. This preamplifier is also
designed to operate in conjunction with the cable preamplifier type QPLE, which is placed close to a
dynamic microphone. The combination of a dynamic microphone plus a QPLE is electrically
equivalent to a microphone MKH 105 etc. It is thus possible, when a Nagra is equipped with "Static
5" to place either a condenser microphone or a dynamic microphone with the QPLE at the end of
the microphone cable.
Sensitivity: 2 mV gives 0 dB when the gain is maximum.
Attenuation of low frequencies: adjustable by steps of 3 dB at 50 Hz up to -15 dB by a built-in
switch. To operate this switch, it is necessary to open the Nagra.
Maximum Input Voltage: 200 mV.
Distortion and noise level: negligible, compared with those of the microphone.
Temperature range: -55? to +71? C (-67? to + 160? F)

"HIGH LEVEL LINE" Code: QPM -6

This preamplifier transforms the microphone input into a symmetrical floating line input. Input
Levels: 0.1 to 24 V R.M.S. Impedance: 10 k Ohm.
(on special order only)

"UNIVERSAL" Code: QPAUT & QPUT

These preamplifiers are designed to accept dynamic 200 Ohm, "Phantom" +12 V or +48 V and "T"
powered +10 V condenser microphones.

The QPAUT composed of the preamplifier itself and the microphone power supply, is intended for
the Mike input No 1, whereas the QPUT intended for the Mike input No 2 is composed of the
preamplifier only, then it cannot be installed alone without the QPAUT.
The QPAUT is externally switchable and the QPUT internally.
Dynamic microphones: Impedance 200 Ohm, frequency response ±1dB 80 Hz to 20 kHz, sensitivity

0.2 mV/µbar, max. input level producing 1% distortion 50 mV.

Condenser microphone: "Phantom" +12 V or +48 V, "T" powered (+10 V), same frequency
response as dynamic ones, sensitivity 1.5 mV/ µbar, max. input level producing 1% distortion 640
mV.

SPECIAL PLUG-IN PREAMPLIFIERS

Filtering Versions of the QPSE

On special request, it is possible to supply "Standard" preamplifiers having a bass attenuation up to
as much as 18 dB at 50 Hz or whose gain is different from the normal value.

Cable Preamplifiers

These preamplifiers are placed near a dynamic microphone. Their power supply is derived from the
Nagra and is transmitted along the same cable as the signal. The Nagra should be equipped with a
condenser microphone preamplifier (see above).

"CABLE SEN 5-200" Code: QPLE 200 and "CABLE SEN 5-50" Code: QPLE 50 (for 50 ?
microphone)

These preamplifiers function in conjunction with the "Static 5" incorporated within the Nagra. The
overall results are equivalent to using the "Standard 200 and 50" (see above)
The low frequency attenuation can be adjusted on the incorporated "Static 5" preamplifier.

LOW FREQUENCY ROLL-OFF ATTENUATORS

Why Filter?

Sound engineers have long known that in certain cases an attenuation of the low frequencies can
improve the subjective quality of the recording, because:

A) Certain microphones (e.g. ribbon) have a frequency response which is very linear, but

only if it is sufficiently distant from the sound source. Placed close to the latter (10 cm),
the bass frequencies are accentuated. This gives, for example, a very "warm" voice, a
phenomenon which certain singers exploit, but which diminishes the intelligibility.

B) A sound studio is constructed and treated in such a manner as to reflect, in the same

proportion, both low and high frequency sounds. When the sound recording is made in
any other room, often the low frequencies are exaggerated, the carpets, curtains and
other absorbent surfaces attenuating essentially the high frequencies, whereas the low
frequencies are integrally reflected.

In the two cases above, the attenuation of the low frequencies only re-establishes the linearity. In
case A) this is clear, but in B) isn't the reality that which we would have heard if the ear was put in
place of the microphone? The ear, however, has the facility of selecting the sounds in function of
their direction and to subjectively attenuate reflected sounds. When recording in mono (and even in
stereo), the microphone captures, without discrimination, all sound which reaches it. Of course, the
directional properties of the microphone can be used, but the reflected bass frequencies can be
behind the sound source and reach the microphone from exactly the same direction as the useful
sound.

In addition to re-establishing the linearity, it has been found that in certain cases, an attenuation of
the low frequencies can, although falsifying the reality, improve the subjective result. In particular, it
can increase the intelligibility. On the other hand, it is sometimes necessary to have recourse to the
attenuation of stage noises. In this case, choose the lesser evil.

When should Filtering be done?

Two solutions are possible, filtering during the recording, or the editing. Method comparison:

A) In filtering during editing (dubbing) it is easy to start again, if an error is made. On the

other hand, if filtering is exaggerated during the recording, the damages are practically
irreparable.

B) In recording linearly, the tape is loaded with signals, which produce a certain

modulation noise. These signals will be eliminated at a later stage, but the noise will
remain.

C) Before passing to dubbing, it is necessary to listen to the sound during the "rushes".

An unfiltered sound is unpleasant and the producer may judge the result in a bad light.

Conclusion

It is recommended to filter during recording, but possibly slightly less than would seem necessary.
There is little chance then of over filtering. The filtering will be finished during editing. In any case,
the use of very good headphones is strongly recommended. Headphones, which cut the very low
frequencies, should be mistrusted as they play the role of filter and mislead the operator.

METERING

MODULOMETER OR V.U. METER

To measure the level of an electrical signal representing a sound, there are two devices available,
the modulometer and the v.u. meter. Both of them are voltmeters whose needle position represents
the level. Their construction and use are however different.

MODULOMETER

The modulometer measures the peak value of the signal, irrespective of the form or the level, the
modulometer takes into consideration the strongest positive or negative value. It is equipped with a
memory, so the signal can be very brief, but the memory ensures that the met er needle advances
and stays there for sufficient time for the operator to read it. The essential advantage of the
modulometer comes from the fact that the measurement it gives is that which concerns magnetic
recording, in other words it is the signal peak , which saturates the tape. The average value of the
signal (as much as it concerns the listener) is of no importance to the tape. In particular, while
recording noise, the modulometer indication is always exact, no matter how long the duration of the
noise.
The scale of a modulometer can be logarithmic, i.e. linear in decibels. In the case of the Nagra, it is
possible, for example, to have a range of 70 dB. This allows the exact appreciation of even the
lowest sound levels. Nevertheless, it is preferable to limit the range from -30 to +5 dB, to help
operators who are used to VU meters, which are not logarithmic.
The operator, on seeing the needle move, knows that his level is greater than -20 dB.

VU METER

In the days of electronic valves (tubes), a modulometer was very costly, and the rudimentary VU
meter was often preferred. Later, it was noticed that the VU meter still maintained a certain following
and because of habit and standards many radio stations still use them.
A VU meter is a simple rectifier voltmeter whose response time has been standardized. If the signal
to be measured is continuous, (e.g. a whistle) the VU meter will indicate a value the same as the
modulometer, but if the signal is intermittent (e.g. speech) the VU meter will only indicate an
average value, i.e. considerably lower than the instantaneous maximum levels.
For speech, it has been found that this average value is approximately 8 dB lower than the peak
value. By increasing the VU meter sensitivity by 8 dB, an indication of 0 VU. is obtained when the
peaks reach the maximum value. This works relatively well in practice. For noise, the indication of
the VU meter evidently becomes very inexact, and renders it practically useless.

The v.u. meter, however, has certain advantages:
a) Speech-music balance. If speech and music are recorded with a modulometer so that

the peaks of the signal do not exceed the maximum level, subjectively the music
appears stronger. This is due to the more continuous character of music signals.
Therefore, in a mixed program, it is necessary to modulate the speech more strongly
than the music. This can be done by modulating the music correctly and over
modulating the speech or by under modulating the music.

It is to be noted that a slight over modulation of speech is not catastrophic: a

transmitter is fitted with a limiter, as in the Nagra 4.2, which cuts peaks exceeding the
maximum level. The subjective deterioration of the sound quality remains
unnoticeable. On the other hand, a strong modulation increases the range of the
transmitter and is of direct interest for commercial radio stations.

A VU meter under indicates the speech. In modulating a program to 0 VU the speech

will be over modulated and the music under modulated. From this point of view, the
VU meter seems to be of more interest for mixed transmissions whose quality is not of
great importance, but whose range should be as large as possible.

On the other hand, for a transmission, which is wholly musical, the range of the

transmitter tends not to be used to its full advantage with a VU meter.

b) The VU meter has a scale, which is not logarithmic. For the needle to move, it is

necessary that the level exceed -20 dB. This causes the operator to compress greater
than is necessary, that is to increase the level of the pianissimo. This reduces the
quality of a musical transmission while increasing the range. On the other hand, it is
favorable if the listener is in a noisy ambience, such a car or a cinema hall.

CONCLUSIONS

The problem to be resolved is to know if the Nagra should be fitted with a modulometer or a VU
meter. The modulometer allows the use of the full dynamic range of the recorder whether for noise,
speech or music. The balance of the sound can, in any case, be achieved during the transfer.
If a mixed transmission of words and music should be recorded on the Nagra and transmitted as
recorded, the operator can simply modulate the speech to +2 dB or even +4 dB, and the limiter
takes charge of any peaks, and the music to 0 or even -2dB.
The VU meter is only justified for radio corporations where it is standardized because of operational
habit.

REMARKS ON THE CALIBRATION

The term "nominal recording level" is that which is considered as the maximum level by habit. The
word "nominal" has been used and not "maximum" as, in the case of the Nagra 4.2, this level can
be exceeded by 4 dB due to a special recording process.

The indication of 0 dB on the modulometer corresponds to the nominal level. It is not measurable
with a VU meter for the needle will exceed full scale deflection, the sensitivity of the VU meter
having been increased by 10 dB to compensate for the slowness of its response.
Thus a signal of -10 dB, that is 10 dB below nominal level, produces on a VU meter an indication of
0 VU whereas on the modulometer an indication of -10 dB is obtained. The calibration generator of
the Nagra 4.2 gives a signal of about -10 dB. This corresponds to 0 VU on a VU meter.

9.0 SPECIFICATIONS

DIMENSIONS AND WEIGHT

Dimensions of the case with the lid closed, without knobs, feet, carrying handle, or carrying handle
mountings:

L X W X H

12.6 x 8.8 x 4.4 "

(320 x 223 x 111 mm)
Overall dimensions without handle
L X W X H

13.2 x 9.6 x 4.5 "

(335 x 243 x 114 mm)
Weight, without batteries or tape 13 lb (5.89 kg)
Weight with ordinary batteries, 5" reels of tape 15lb (6.8 kg)

POWER SUPPLY

(Supply voltage, positive ground) –10.5 to -30 V DC.
from –10.5 to -12 V some performances are slightly reduced

Current consumption
in Test 95 mA

in Line Playback 180 mA
in Loudspeaker Playback, average level 250 mA
in Record 240 mA
in Fast Rewind 280 mA

Type of batteries used (12 cells)
CEI standard R 20

ASA standard D and L 90
Approximate length of battery life if used 2 hours every 24 hours
Eveready 950 batteries 18 hours

Eveready E95 batteries 32 hours
Continuous use with Eveready 950 batteries 8 ½ hours

Recording time at 7½ ips (19 cm/s) with 35µm tape 45 min.
Maximum reel diameter with lid closed 5" (127 mm)

Recording time under the same conditions 22 min.
Rewind time with 5" reel (19 cm/s) with 35µm tape 20 min.

TAPE TRANSPORT

Switchable nominal speeds
15 ips 38.10 cm/s

7½ ips 19.05 cm/s
3¾ ips 9.525 cm/s

Stability of the nominal speed with respect to the temperature (within the specified range), the
position of the recorder, the distribution of the tape between the reels, and the supply voltage ±0.1%

WOW AND FLUTTER

Weighted peak-to-peak value, in accordance with
DIN 45 507/ANSI 4372

at 15 ips 38.10 cm/s ±0,05 %
at 7½ is 19.05 cm/s ±0.07 %
at 3¾ ips 9.525 cm/s ±0.12 %

AMPLIFIER CHAIN

NAGRA 4.2 with QPSE-200-XOYO preamplifiers
Overall frequency response, 200 Ohm microphone

input, line output without load from 50 Hz to 20 kHz ±1 dB
Total distortion at 0 dB, 10 mV input, output load 600 Ohm <0.3 %

Input voltage for 1% distortion at 1 kHz 65mV
Noise level of the microphone preamplifier, ASA A

Weighted, 1 mW reference -126 dBm

MAGNETIC TAPE

Width 6,25 mm
Mixer direct input, impedance 9 k Ohm,
voltage for recording at 0 dB 560mV
Pilot input, impedance 5 k Ohm,
admissible voltage 0,5 to 25 V

AUTOMATIC LEVEL CONTROL

Input voltage for recording at nominal level 0.65 to 22 mV
Average distortion at 1 kHz within this range, 3rd harmonic 0,3%
Frequency response from 55 Hz to 16 kHz ±1.7 dB

FILTERS

LFA 1 (low frequency Attenuation
attenuation) 4 dB at 50 Hz
LFA 2 8 dB at 50 Hz
HP 1 (high-pass) 10 dB at 50 Hz
HP 2 20 dB at 50 Hz
HP 1 + LFA 1 (combination) 14 dB at 50 Hz

REFERENCE GENERATOR

1.1 kHz sine wave signal with 10 kHz component

0 VU level= -8 dB ±0.1 dB

OUTPUTS

Line output voltage on 600 Ohm for 0 dB on the modulometer 4.4 V
Line output impedance at 30 Hz 90 Ohm

at 50 Hz 42 Ohm
at 1 kHz 18 Ohm
at 15 kHz 24 Ohm

Maximum output voltage on 600 Ohm,
for 1% distortion at 1 kHz 10,5 V

at 5 kHz 10,5 V
at 30 Hz 7,0 V

Headphones output voltage on 50 Ohm, adjustable from 20 to 500 mV
Output voltage at MIXER connector, on 100 k Ohm, for 0 dB on the modulometer 560 mV
Output voltage of the pilot signal
with QSLI synchronizer 1 V

without synchronizer 350 mV

BUILT-IN LOUDSPEAKER

Power output of the amplifier 1 W

OPERATING CONDITIONS

Temperature
with manganese batteries - 4 to + 160 degrees F

-20 to + 72 degrees C

with external power -67 to + 160 degrees F

-55 to + 71 degrees C

The recorder operates correctly in any position.

MODULOMETER

Integration time for - 2 dB 7.5 ms
Usable scale -30 to +5 dB
Frequency response
from 40 Hz to 20 kHz ±0,5 dB

RECORDING AND PLAYBACK CHAIN
Nominal recording level 0 dB= 320 nWb/m
Maximum peak level (M.P.L.) + 4 dB

Magnetic tape used for Calibration :
CCIR LN PEM 468

STD PER 368
NAB LN 3M 808

STD 3M 806
Erasing efficiency
CCIR 84 dB

NAB 88 dB
Frequency response, recording at 20 dB below M.P.L.
15 ips (38 cm/s) CCIR and NAB 30 Hz to 20 kHz ±1.5 dB

7½ ips (19 cm/s) CCIR and NAB 30 Hz to 15 kHz ±1.5 dB
3¾ ips (9,5 cm/s) CCIR and NAB 30 Hz to 8 kHz ±2.0 dB

Distortion at M.P.L :
CCIR 3rd harmonic 0,4%

2nd harmonic 0,3%
NAB 3rd harmonic 1,0%

2nd harmonic 0,4%
Signal-to-noise ratio of the playback chain only, with motor running and leader tape, ASA A

weighted, M.P.L 83 dB
Recording-playback signal-to-noise ratio at M.P.L at 7½ ips

ASA A
Linear Weighted

LN NAB 64 dB 73 dB
CCIR 62 dB 72 dB

STD NAB 64 dB 70 dB
CCIR 62 dB 68 dB

INPUTS

NAGRA 4.2
with QPSE-200-X0Y0 preamplifiers

Microphone input 1,200 Ohm 0.2 to 43 m V
Microphone input 2,200 Ohm 0.2 to 43 m V

Unbalanced line input, impedance 100 k Ohm
admissible voltage 0.37 to 120 V

Unbalanced line input at accessory connector,
admissible current 3.7 to 1,200 µA

Mixer direct input, impedance 9 k Ohm 560 mV
Pilot input, impedance 5 k Ohm 0.5 to 25 V