NTI A2 User Manual
User Manual
A2
Audio Test & Measurement System
interstage
Phistersvej 31, 2900 Hellerup, Danmark
Telefon 3946 0000, fax 3946 0040
www.interstage.dk
- pro audio with a smile
V
3.1 / July '01 / Ben
N:\A2Proj\#Manuals\User Manual\English\a2um_31e_nti.doc
Test & Measurement System
Version 3.1E
A2 firmware V2.0 or higher
User Manual A2 Audio Test & Measurement System
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A2 Audio Test & Measurement System User Manual
CE DECLARATION OF CONFORMITY
We, the manufacturer
hereby declare that the product
Product Name Audio Test & Service System
Model Number A2
Year of Construction 1995
conforms to the following standards or other normative documents
EC-Rules 89/392, 91/368, 93/44, 93/68, 73/23, 89/336, 92/31
Harmonized Standards IEC 65, IEC 68-2-31, IEC 348
EN50081-1, EN50082-1, EN50140, EN 61010-1
This declaration becomes void in case of any changes on the product without written
authorization by NTI.
Date Schaan, 28. 02. 1995
Signature
Position of Signatory Product Manager Test Instruments
Principality of Liechtenstein, Europe
Samples of this instrument have been tested and found to
conform with the statutory protective requirements. Instruments of
this type thus meet all requirements to be given the CE mark.
NTI AG
Im alten Riet 102
FL - 9494 Schaan
V3.1 3 / 104
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A2 Audio Test & Measurement System User Manual
INTERNATIONAL WARRANTY
Limited Warranty
NTI guarantees the A2/A2 -D Audio Test & Service System and its components against
defects in material or workmanship for a period of one year from the date of original
purchase, and agrees to repair or to replace any defective unit at no cost for either parts or
labour during this period.
Restrictions
This warranty does not cover damages that have resulted of accidents, misuse, lack of care,
the attachment or installation of any components that were not provided with the product,
loss of parts or connecting the instrument to any other power supply, input signal voltage or
connector type than specified. In particular, no responsibility is granted for special, incidental,
or consequential damages.
This warranty becomes void if servicing or repairs of the product are performed by any other
party than an authorized service center.
No other warranty, written or oral, is authorized by NTI. Except as otherwise stated in this
warranty, NTI makes no representation or warranty of any kind, expressed or implied in law
or in fact, including, without limitation, merchasing or fitting for any particular purpose and
assumes no liability, either in tort, strict liability, contract or warranty for products.
Note
In case of malfunction, take - or ship prepaid - your NTI A2/A2 -D Audio Test & Service
System, packed in the original packing, to your nearest authorized service center. Be sure to
include a copy of your sales invoice as proof of purchase date. Transit damages are not
covered by this warranty.
Principality of Liechtenstein, Europe
Tel. +423 – 239 6060
Fax +423 – 239 6089
E-mail info@nt-instruments.com
NTI AG
Neutrik Test Instruments
Im alten Riet 102
FL - 9494 Schaan
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User Manual A2 Audio Test & Measurement System
TABLE OF CONTENTS
1. INTRODUCTION ...........................................................................................10
Safety Information ............................................................................................................... 10
Overview.............................................................................................................................. 10
How to use this Manual....................................................................................................... 12
2. INSTALLATION.............................................................................................13
Unpacking............................................................................................................................ 13
Options and Accessories..................................................................................................... 13
Environmental Conditions ................................................................................................... 13
Mains Power Supply....................................................................................................... 13
Printer Connection.......................................................................................................... 14
Interface to PC................................................................................................................ 14
3. GETTING STARTED .....................................................................................15
Measurement Functions ...................................................................................................... 15
Menu Operation...................................................................................................................15
Generator Settings .............................................................................................................. 16
The Display Modes..............................................................................................................16
Sweep Operation............................................................................................................17
The A2/A2-D User Interface................................................................................................18
A2/A2-D Menu Overview.....................................................................................................19
4. A2/A2-D OPERATION .................................................................................21
Input Section........................................................................................................................21
Input Block Diagram........................................................................................................ 22
Input Wiring & Impedances.............................................................................................22
Input / Output Impedance Selection.................................................................................23
Auto / Fixed Range........................................................................................................24
Connection of a Balanced Output to the A2/A2-D.............................................................25
Connection of an Unbalanced Output to the A2/A2-D.......................................................25
Monitor Outputs............................................................................................................... 26
Monitor Loudspeaker......................................................................................................26
Overview.........................................................................................................................26
Output Section..................................................................................................................... 27
Output Circuit.................................................................................................................. 27
Balanced Operation .......................................................................................................28
Unbalanced Operation...................................................................................................28
Optional Transformer Output Stage.................................................................................28
Output Settings ............................................................................................................... 29
Output Parameters.........................................................................................................29
Signal Waveform...........................................................................................................29
Square Signal (Sym. / Asym.).........................................................................................30
IMD TestSig ..................................................................................................................30
Noise............................................................................................................................31
Warbled Sine.................................................................................................................31
Frequency.......................................................................................................................31
Level................................................................................................................................31
Readback........................................................................................................................32
Output Muting.................................................................................................................. 33
Overview.........................................................................................................................33
Display Modes.....................................................................................................................34
METER Display Mode..................................................................................................... 34
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Generator Settings.........................................................................................................35
Generator Readback......................................................................................................35
Measurement Results ....................................................................................................35
Units.............................................................................................................................35
The Bar-graph ...............................................................................................................36
Zooming the Bar-graph Scale.........................................................................................36
Scrolling the Bar-graph...................................................................................................36
Input Display..................................................................................................................37
Printouts........................................................................................................................37
GRAPH Display Mode....................................................................................................38
Cursor Function.............................................................................................................39
Y-Scaling.......................................................................................................................39
ZOOM...........................................................................................................................39
SCROLL.......................................................................................................................40
X-Scaling.......................................................................................................................40
GRAPH Printouts...........................................................................................................41
Store & Recall Graphs ....................................................................................................41
SCOPE Display Mode..................................................................................................... 42
Printouts........................................................................................................................43
Overview.........................................................................................................................43
5. MEASUREMENT FUNCTIONS .......................................................................44
Level Function ..................................................................................................................... 44
Mono / Stereo Measurements........................................................................................44
Units ................................................................................................................................ 44
Filters............................................................................................................................... 45
Applications..................................................................................................................... 46
Overview.........................................................................................................................46
Level Relative Function....................................................................................................... 47
Filters............................................................................................................................... 47
Units ................................................................................................................................ 48
Application Example.......................................................................................................48
Signal-to-Noise Measurement........................................................................................48
THD+N Function..................................................................................................................49
Notch Filter...................................................................................................................... 50
Additional Filters.............................................................................................................. 50
Units ................................................................................................................................ 50
SINAD Measurement......................................................................................................51
IMD Function.......................................................................................................................52
Standards ........................................................................................................................ 53
Unit.................................................................................................................................. 54
Filters............................................................................................................................... 54
Applications..................................................................................................................... 54
Noise Function.....................................................................................................................55
Units ................................................................................................................................ 55
Filters............................................................................................................................... 55
Applications..................................................................................................................... 56
Noise Relative Function ...................................................................................................... 57
Units ................................................................................................................................ 57
Filters............................................................................................................................... 57
Crosstalk Function...............................................................................................................59
Units ................................................................................................................................ 59
Filters............................................................................................................................... 59
External Source.............................................................................................................60
Level Selective Function..................................................................................................... 61
Filters............................................................................................................................... 61
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External Source.............................................................................................................62
Units ................................................................................................................................ 62
Applications..................................................................................................................... 62
Wow & Flutter Function....................................................................................................... 63
Standards ........................................................................................................................ 64
W&F Measurements (Replay only).................................................................................64
W & F Measurements (Record to Replay) ..................................................................... 64
W&F Signal Analysis....................................................................................................... 65
Phase Function.................................................................................................................... 66
Applications..................................................................................................................... 66
Filter Overview.....................................................................................................................67
ADDITIONAL Function........................................................................................................67
6. SWEEPS .....................................................................................................68
Preparing a Sweep.............................................................................................................. 68
Selecting the Sweep Mode............................................................................................. 68
Setting the Sweep Limits & Resolution.......................................................................... 69
Performing a Sweep............................................................................................................ 70
Synchronization (Internal / External).............................................................................. 70
Sweep Recording................................................................................................................ 71
Keep a Recorded Trace.................................................................................................. 71
Store & Recall Sweeps...................................................................................................71
Sweep Modes...................................................................................................................... 73
Frequency Sweep........................................................................................................... 73
Y-Axis Units and Scaling................................................................................................73
Re-Scaling of the Frequency Axis ...................................................................................73
Frequency Sweeps in Different Measurement Modes .......................................................74
Graphics Cursor.............................................................................................................74
Tape Sweep.................................................................................................................... 75
Recording a Tape Sweep...............................................................................................75
External Sweep............................................................................................................... 77
Preparing an External Sweep.........................................................................................77
List of Reference CD Tracks ...........................................................................................78
Stepped Sweeps............................................................................................................78
Gliding Sweeps..............................................................................................................78
Amplitude Sweep............................................................................................................ 79
Units of X- / Y-axis.........................................................................................................79
Time Sweep .................................................................................................................... 80
Table Sweep................................................................................................................... 81
Sweep Data Upload to a PC............................................................................................... 81
7. PRINTOUTS.................................................................................................82
Printer Driver Selection........................................................................................................ 82
Printer Settings....................................................................................................................83
EPSON FX-80, IBM Proprinter .......................................................................................83
EPSON LQ-550 / LQ-1050............................................................................................. 83
hp Laserjet, Deskjet........................................................................................................ 83
Printer Error......................................................................................................................... 83
8. INSTRUMENT SETUP ...................................................................................85
Store & Recall Setups ......................................................................................................... 85
Calibration............................................................................................................................ 85
Connector Pin Assignment.................................................................................................. 87
Centronics Connector..................................................................................................... 87
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Timing Diagram .............................................................................................................87
RS232 Connector...........................................................................................................87
Cable............................................................................................................................88
9. OPTIONS & ACCESSORIES..........................................................................89
Options Overview................................................................................................................ 89
RS232 Serial Interface (AO1 / AO16).............................................................................90
Baudrate Selection.........................................................................................................90
Filter Options................................................................................................................... 91
A-Weighting Filter (AO4).................................................................................................91
User Filter (AO5)............................................................................................................92
C-Message Filter (AO13)................................................................................................93
80kHz Lowpass Filter (AO14) .........................................................................................94
Transformer Option (AO7).............................................................................................. 95
Phantom Power (AO8)....................................................................................................95
Accessories Overview.........................................................................................................95
10. TECHNICAL SPECIFICATIONS ......................................................................96
Analog Generator................................................................................................................ 96
Digital Generator ................................................................................................................. 96
Sweep Function...................................................................................................................96
Analog Analyzer................................................................................................................... 96
Digital Analyzer.................................................................................................................... 97
Level Function ..................................................................................................................... 97
Total Harmonic Distortion (THD + N)..................................................................................97
Phase................................................................................................................................... 97
IMD ...................................................................................................................................... 97
Crosstalk / Level Selective .................................................................................................. 98
Noise.................................................................................................................................... 98
Wow & Flutter Function....................................................................................................... 98
Drift ...................................................................................................................................... 98
Frequency Function............................................................................................................. 98
Scope Function.................................................................................................................... 98
Filters ................................................................................................................................... 99
Display (of A2/A2-D)............................................................................................................ 99
Interfaces.............................................................................................................................99
General Data ....................................................................................................................... 99
11. INDEX........................................................................................................100
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1. INTRODUCTION
Safety Information
Please read this safety information thoroughly before starting to operate the A2.
• The NTI A2/A2-D Audio Test & Measurement System was designed to be connected to a
specified mains power source with safety grounding through an approved three -wire
mains power cable.
NEVER operate the instrument with missing or compromised
• To avoid fire hazard, the mains power fuse of the A2/A2-D must be replaced in case of
failure by a fuse with the correct rating (see chapter 2. Installation).
• For safety reasons never apply voltages higher than 200V
measurement inputs of the A2. Voltages higher than that may permanently destroy the
internal electronics.
• There are no parts inside the instrument that may be repaired or replaced by the user.
Therefore, never open the unit for any reason.
Do not try to service the instrument unless properly qualified.
safety ground connection.
or 300Vp to the
RMS
Overview
The NTI A2 is a comprehensive, high performance two -channel audio test set. It includes a
flexible generator, based on a Digital Signal Processor (DSP) and a high performance
analyzer providing a wide variety of measurement functions, as there are
• Level absolute (two-channel) in µV, mV, V, dBV and dBu or dBm
• Level relative in *1, % and dBr
• Level selective in µV, mV, V, dBV and dBu / dBm
• Total harmonic distortion & noise (THD+N) in % and dB
• IMD (Intermodulation distortion) in % and dB
• Wow & Flutter in %
• Noise (absolute), weighted and unweighted, in µVq, mVq, Vq and dBq
• Noise (relative), weighted and unweighted, in *1, % and dBr
• Crosstalk (frequency selective) in *1, % and dBr
• Frequency (two channels simultaneously)
• Phase (interchannel) in the range of ±180°.
In the METER display mode, all measurement results are displayed in numerical form as
large digits and in analog form through a bar-graph. Additional parameters like the I/Ofrequencies and impedances, the input levels and the generator settings are permantly
shown.
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The standard sweep capabilities of the A2/A2-D allow to perform
• Frequency sweeps
• Amplitude Sweeps
• Time Sweeps
• Table sweeps with freely definable pairs of frequency and level (with Option AO1)
Sweeps can be controlled by the built-in generator or by an external source (e.g. test tapes,
test CDs or other NTI A-series instruments) at a remote location. Several traces can be
recorded and displayed in the GRAPH mode, while up to four complete graphs may be
stored in the internal non-volatile memory of the A2/A2-D. This allows for instance to record
swept measurements in a studio and to print out the results in the office later.
Another powerful diagnostic aid of the A2 is the SCOPE function. In this mode, the waveform
of both input channels is shown on the LC-display just like on a dual trace oscilloscope. If set
to the THD+N function, the A2/A2-D shows both the original signal and the distortion
residual. In other measurement functions, the main input signal is shown as a single trace.
All measurements of level - except noise - are true RMS rectified. Noise is measured as
quasi-peak value according to the CCIR 468-3 standard. Both a 400Hz high -pass and a
22Hz-22kHz band-pass filter are available as a standard.
The two inputs of the A2/A2-D are DC -isolated up to ±300Vp, and equipped with selectable
input impedances to optimally match the output impedance of the device under test (DUT).
As an option, both inputs may also be Phantom-powered.
The normalized input signals are available at the BNC connectors at the rear panel of the
instrument. A small, built-in loudspeaker allows acoustical monitoring of the measured signal.
The versatile generator of the A2/A2-D, based on a Digital Signal Processor, is capable of
generating a large number of different test signals over the full level & frequency range.
• Low distortion pure sine signal
• Low distortion warbled sine
• Dual-tone IMD signal, covering all standards
• Symmetric square wave (50:50 duty cycle)
• Asymmetric square wave (40:60 duty cycle for phase reverse check)
• White noise
• Pink noise
The output impedance (<15Ω up to 600Ω) can be adjusted in a wide range as well in order to
match the input impedance of the device to be tested.
As an option, a RS-232 serial or IEEE-488 parallel interface may be installed into the
instrument to remote control all A2/A2-D features from a PC.
Regardless of the type of interface, AS04, a comprehensive Windows based software
package is included, supporting all operation modes, offering the possibility to store all
results, and allowing to write program sequences in the easy-to-learn Audio Measurement
Sequence Language (AMSL) for fully automatic measurements.
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User Manual A2 Audio Test & Measurement System
How to use this Manual
This User Manual has been written to serve as a complete reference document for using the
A2/A2-D as a solution for your measurement requirements. Maintenance procedures, such
as installation of the instrument, are placed at the beginning while not so frequently required
tasks such as re-calibration are filed at the end of the manual.
The best way to familiarize with the instrument is to place the A2/A2-D in front of you and to
read through the chapters 2. Installation and 3. Getting Started. This way, it won't take long to
feel at ease with the instrument and its many features.
Do not operate the instrument without reading through the chapter
2. Installation. Important information about mains voltage selection and fuse
rating is given therein.
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1
0
2. INSTALLATION
Unpacking
Your new A2/A2-D comes along together with some accessories. Please check whether all
of the following items are enclosed.
• A2/A2D Audio Test & Service System
• Mains power cable
• Spare fuse for 110VAC
• A pair of rack-mount wings
• This User Manual.
It is strongly recommended to save the original cardboard box for the case that it ever
becomes necessary to ship the A2/A2-D. Never ship the instrument in a box not properly
protecting the unit against mechanical shock, since the NTI warranty does not cover
damages caused by improper packing.
Options and Accessories
Besides the wide range of already built-in features of the A2/A2-D, there are some optional
items available for the A2/A2-D as listed in chapter 8. Instrument Setup. Please ask your local
NTI agency for further details.
Environmental Conditions
The A2/A2D test system will operate in accordance with its specifi cations as long as the environmental conditions are kept within the following ranges.
Temperature 5°-45° Celsius
Humidity 10 -90% non condensing
Mains Power Supply
After having unpacked the unit, it is first necessary to connect the system to the AC mains
power of your country. For this purpose, the enclosed mains power cable has an unconnected end with three colored leads, corresponding to
Brown = Live
Blue = Ground
Green/Yellow = Earth
Attach a mains plug to this end of the cable, fitting to the receptacles of your area. Next,
make sure that the mains power voltage matches the power selection that is shown on the
mains power connector/fuse holder assembly on the rear panel of the A2/A2-D. If this selection is incompatible with the available power source, go through the following paragraph to
adjust the mains power requirements.
The A2/A2-D2 can operate from 100VAC, 120VAC, 230VAC or 240VAC. To configure the
input line voltage of the A2/A2-D, remove the mains cable and open the flap of the
connector/fuse holder assembly at the rear panle of the A2/A2-D by pressing a small
screwdriver into the slot on the top or ruin your fingernails.
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1
0
Take out the drum and insert it in the new, required position.
The label pointing towards the operator indicates the selected
line voltage.
At the same time, insert a new fuse with the proper current
rating must. For 100VAC and120VAC, a 2A fuse has to be
used, while for 230VAC and 240VAC a 1A fuse is required.
After having set the required line voltage and installation of the
proper fuse, close the flap and insert the power cable.
The A2/A2-D is designed to be connected to protective ground (earth) through the ground
wire in the power cable. This connection is essential for safe operation.
NEVER operate the instrument if the safety ground connection is not available or
has been compromised.
Printer Connection
The CENTRONICS printer connector is located at the rear panel of the A2/A2 -D. It is a 25pin female D-type connector - the same as installed in a standard PC.
To select the required printer driver, please refer to the chapter 7. Printouts. The appendix
describes in detail the pin assignment and the timing of the CENTRONICS port.
Interface to PC
Connection The RS232C serial or IEEE-488 parallel interface is available as an option
together with the software package AS04 to control the A2/A2-D as a remote unit. As long as
this interface is not installed, the hole for the connector is covered with a blanking plate.
Both interface types can be upgraded at a later time by inserting a sub circuit. Please refer to
the chapter 8. Instrument Setup for more detailed information.
RS 232 / IEEE (optional)
0 1 2 3 4 5 6 7
Centronics Printer Port
Fig. 1 Rear Panel Interface Connectors
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. To confirm the chosen entry,
(« »)
3. GETTING STARTED
Read this chapter carefully to become familiar with the operation of the A2/A2-D.
Further details are filed in the following chapters.
The NTI A2/A2-D system is very easy to operate, despite its large number of functions and
the variety of options & settings. Since the user interface is arranged in logical blocks and
every key correlated to a certain function, operation of the unit is virtually self-explaining.
Nevertheless, regardless of the keys that are pressed, the internal logic of the system takes
care that every measurement is done according to the specified standards.
Measurement Functions
The measurement-related keys are arranged on the top row of the right hand side of the
A2/A2-D keyboard. Any measurement function may be selected at any time by pressing the
respective key.
Fig. 2 Measurement Function Keys
Some of the keys provide two selections, thus allowing to select another related
measurement (e.g. <THD+N> and <IMD>). To activate the second function, simply press the
key once more and the measurement mode will toggle. The actually selected function is
permanently displayed.
Menu Operation
To allow the user to activate a special option or setup, several menus may be opened by
double-clicking any of the keys marked with a capital "M" in the bottom right (see p. 19).
As soon as the menu is open, a list of selections appears,
with the currently active selection being displayed in inverted
characters.
In this example, by double-clicking the <GEN SIGNAL> key,
the Alt. Signal menu appears.
To change the actual setting, the small triangle arrow on the
left hand side may be moved to any entry of the menu by
turning the <SCALE> wheel
press the <SCALE> wheel once.
If a new selection has been confirmed, the menu will be
closed. Alternatively, leave the menu through the EXIT entry
or by prressing any key.
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(« »)
NOTE While a menu is open, any other keypress than to the <SCALE> wheel
will close the menu and execute the new command.
Generator Settings
The generator output frequency & level can be selected by the two softwheels labeled with
<FREQUENCY> and <LEVEL>.
By turning the <FREQUENCY> or <LEVEL> wheels slowly or quickly, the width of the step
up/down to the next value may be small or large as listed in Table 1.
<FREQUENCY> <LEVEL>
Coarse mode, quick turn 10Hz - 20Hz - 100Hz - 1kHz -
10kHz - 40kHz - 100kHz
Coarse mode, slow turn ± 12.5% ± 2dB / ± 25.9%
Fine mode, quick turn 3rd-octave steps ± 2dB / ∼ factor 2
Fine mode, slow turn ± 0.5% ± 0.04dB / ± 0.5%
Furthermore, the two generator outputs A and B can be muted by pressing the respective
<MUTE> keys. Otherwise, i.e. if they are muted, both outputs are permanently active.
Neither frequency nor level can be changed
continuously - as with a poti-controlled analog
generator - but in discrete steps only.
By pushing the softwheel once, the stepwidth
toggles between fine (< >) and coarse
mode. The actual selection is indicated by a lit
LED behind the corresponding sign.
Table 1 Softwheel Steps
± 20dB (logarithmic units)
or factor 10 (linear units)
The Display Modes
With the three DISPLAY MODE keys, the user may select one of the available modes, regardless of the actual measurement function.
All these modes can be selected at any time without affecting the actual measurement (e.g.
also during a running sweep).
To increase the lifetime of the backlight of the LC-display, it is automatically switched Off if
no key or wheel on the instrument is used for several minutes. However, any keypress immediately re-lights the illumination.
• The METER mode displays the single results together with all additional measurement parameters.
• Sweeps may be displayed in the GRAPH mode.
• The SCOPE mode shows the waveform of the
input signal in the time domain.
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Sweep Operation
Sweeps are best performed in the display mode GRAPH, that continuously displays the
setup parameters and the recorded curve(s) on the LCD.
The specific sweep setup may be selected through the keys of the SWEEP block.
Fig. 3 SWEEP Block
Basically, there are 5 sweep modes available, that can be called through the menu behind
the key <SWEEP MODE>.
• Frequency sweeps measure the actually selected function vs. a changing frequency
• Tape sweeps allow to record a defined frequency pattern on a tape
• Amplitude sweeps measure the actually selected function vs. a changing amplitude
• Time sweeps measure the actually selected function vs. time
• Table sweeps allow to measure the actually selected function vs. a previously defined
frequency / amplitude table (requires RS232 or IEEE-488 option)
Furthermore, the <SWEEP MODE> key allows to toggle between internally and externally
generated sweeps.
To define the start / stop value of the X-axis (e.g. 20Hz / 20kHz for a frequency sweep), set
the generator to the desired value and press the <START> / <STOP> key respectively.
Choose the resolution of your sweep, i.e. the number of samples to be recorded, through the
<RESOLUTION> key. Both modes (LOW / HIGH) allow to set the required number of measurements by entering the sweep resolution menu.
The recording of a new sweep is started by pressing the <DO SWEEP / STOP> key, while a
running sweep may be stopped through the same action.
Several sweeps may be permanently stored by entering the menu behind the <GRAPH>
button, and selecting one of the four avilable memory locations (M1-M3). By this way, up to
four complete graphs with a max. of 6 curves per graph may be stored in the non-volatile
memory of thze A2/A2-D for a later printout or upload to a PC.
NOTE This is only a very brief description of the sweep capabilities of the A2.
Please refer also to the chapter 6. Sweeps to see all the possibilities.
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The A2/A2-D User Interface
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A2/A2- D Menu Overview
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4. A2/A2-D OPERATION
NOTE Before switching On your A2/A2 -D, make sure that the selected mains
power voltage matches the one of your area. If not, please refer to chapter 2. Installation to set it correctly.
Each time the A2/A2-D is switched On, it perform s a short self-test, during which the A2 logo
will be displayed together with the software version, the current time setting of the internal
clock and the serial number of the unit.
After this test, the A2/A2-D will present itself in the last active setup, i.e. show the same settings and selections as when it was switched off. Nevertheless, it is also possible to define
and recall a user setup (see chapter Store & Recall Setups).
The A2/A2 -D is equipped with a screen saver function to extend the life time of the LCD
backlight. The backlight darkens after ~10 minutes without any operator activity. To turn it On
again, simply press any key or softwheel.
Input Section
The A2/A2-D is a two-channel measurement system, providing two fully independent measurement channels, named MAIN and ALTERNATE. Both channels are equipped with an in-
put impedance circuitry, input attenuators/amplifiers and a filter bank. This allows e.g. to
measure weighted or unweighted levels of both channels simultaneously.
Additionally, the main channel analyzer is equipped with a special filter section for Harmonic
Distortion, Intermodulation and Noise measurements, and also provides the demodulator and
filtering for W&F measurements.
The <A / B> key allows to select which of the input connectors shall be the main channel of
the instrument. In other terms, the input signal of the illuminated (i.e. active) channel is always fed to the main channel, while the other input signal is fed to the alternate channel.
If necessary, one may tilt the instrument
slightly either by turning the carrying handle
below the underside or use the reversible
footings in order to optimze the view on the
LCD.
Furthermore, you may adjust the contrast of
the LC-display to your demands by turning
the potentiometer wheel on the left hand side.
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Input Block Diagram
Fig. 4 Block Diagram Analyzer
Input Wiring & Impedances
Both input channels are fully balanced and terminated with defined impedances right behind
the input connectors Three settings are available.
• The highest possible impedance terminates the
inputs with 100kΩ, corresponding a voltage
matching by means of a minimum load to the
output of the device under test.
• The second value, 600Ω, is intended for all instruments with this output impedance.
• The low input impedance can be set to 150Ω or
200Ω.
Choose one of these three settings by pressing the <IMPEDANCE> button. Each keypress
will toggle to the next impedance. The actually selected impedance is displayed on the left
hand side on top of the METER panel.
NOTE As soon as a level of more than 20V is applied to one of the inputs, the
LOW and MEDIUM impedance selections will be disabled automatically
to protect the inputs from being destroyed. An alert message will inform
you accordingly in this case.
If the LOW impedance is activated, NEVER apply an input voltage > 60V, since
higher voltages can permanently destroy the electronics!
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impedance, or to let the operator fix one impedance while having
the other one switchable. To select your preference, move the
ur selection by
pushing the <SCALE> wheel once. Always leave the menu
capacitor type microphone. Please notice, that the Phantom
d input impedance
The figure below shows the simplified input wiring and the connector pin assignment of one
channel. The circuit is a true instrument-grade differential input. Both input pins (2 and 3) are
loaded with ~100kOhm to ground. Additionally, the input impedances are applied between
the two pins. The inputs are fed to the microprocessor-controlled input attenuator/amplifier,
that adjusts the level of the input signal in order to achieve a high dynamic range at very a
very low distortion.
Input / Output Impedance Selection
In addition to the input impedance selection, a menu is available to choose all available configurations of the input and output impedances. To enter this menu, double -click on the
<IMPEDANCE> key.
The Imped. menu allows either to couple the input to the output
arrow with the <SCALE> wheel and confirm yo
through the EXIT entry.
Optionally, the input connectors of the A2/A2-D can be equipped
with a +15VDC or +48VDC Phantom power to directly connect a
power option replaces the LOW input impedance. Please refer to
chapter Phantom Power (AO8) for more details.
Depending on the configuration, the displaye
on the second line on the METER display, reads Inp 200, Inp 150
or Phantom .
NOTE If the Phantom power option is installed, the 200 Ω (150Ω) input imped-
ance is not available.
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Auto / Fixed Range
The menu behind the <A / B> key allows you to choose between the Auto and Fixed range
setting. In the Auto range mode, i.e. the normal mode, the operator never has to wo rry about
the settings of the input amplifiers.
However, for some applications like testing short bursts, it might be helpful to lock the amplifiers in a certain state.
To lock the input attenuators/amplifiers to a fixed range, proceed as follows.
• Apply the input signal, to which you want to adjust the ranging.
• Call the Ranging menu by double-clicking to the <A / B> button.
• Select the entry Fixed by positioning the arrow through the <SCALE> wheel. Push the
wheel once to activate the setting (the menu closes automatically). The input stages are
now fixed, and all measurements will be performed in this mode.
• To switch back to automatic ranging (normal mode), enter the menu again and select
Auto.
NOTE The input attenuators/amplifiers of the analyzer remain fixed in their
range as long as the Fixed range mode is active.
The Fixed range selection locks the input attenuators/amplifiers
in their actual state as soon as it is chosen by a push on the
<SCALE> softwheel.
If the input signal level is under or over the actual Fixed range,
then the messages TOO LOW or TOO HIGH will appear on the
LCD instead of a measurement result.
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Connection of a Balanced Output to the A2/A2-D
The device under test (DUT) is connected between pin 2 (IN +) and pin 3 (IN -) of the XLR
input connector. The shield may be connected to pin 1, but do not ground the shield on both
ends of the connection, in order to avoid ground loops.
D.U.T.
Balanced
output
Fig. 5 Balanced Connection to the A2/A2-D
ATTENTION ! !
Shielded cable
Avoid ground loop
Input A2
Ground shield
only one side
Connection of an Unbalanced Output to the A2/A2-D
The device under test (DUT) is connected between pin 2 (Signal +) and pin 3 (GND) of the
XLR input connector.
D.U.T.
+
-
ATTENTION ! !
Shielded cable
Input A2
Ground shield
only one side
Avoid ground loop
Be sure not to have
internal connection!
Fig. 6 Unbalanced Connection to the A2/A2-D
NOTE Never c onnect pin 1 and pin 3 together as long as you are not absolutely
sure, that the GND output of the DUT is galvanically isolated from earth.
If in doubt, leave pin 1 of the A2/A2-D unconnected to avoid earth loops.
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Monitor Outputs
There are three BNC connectors and one headphone jack in the MONITOR section on the
rear panel, providing monitor signals for further processing. Output impedance through the
headphone connector is ~68Ω, while the BNC connectors have an impedance of 600Ω.
MONITOR
MAIN
ALT
CHANNEL
READING
HEADPHONE
CHANNEL
The two connectors MAIN CHANNEL and ALT CHANNEL offer
the signals of each input channel right behind the input amplifiers. The level of these signals are always around 1V (0dBV).
The third BNC output offers the READING signal, which is the analogue signal of the MAIN
channel after all the filtering and weighting, but before its rectification (see Input Block
Diagram).
Please notice, that the signal provided at the READING output is not necessarily the same
as at the two other connectors. Depending on the actual measurement function, the character of the READING signal will be totally different from the two other outputs (e.g. with meas-
urement function THD + N or IMD). More detailed information about this topic are given in the
respective chapters describing the measurement functions.
NOTE The MONITOR outputs are not calibrated and shall not be used for
measurements.
Monitor Loudspeaker
The READING signal is also fed to the internal loudspeaker. The volume can be changed
through the potentiometer on the front panel, marked with the loudspeaker sign.
Overview
• The input impedances may be selected through the <IMPEDANCE> key.
• The unit may be operated in the balanced or unbalanced mode, by setting the <FLOAT
GND> switch on the rear panel accordingly.
• Double-clicking to the <A / B> key opens a menu to select either Auto or Fixed ranging.
• The monitor speaker reflects input signal after the input stage and filtering. Its volume can
be controlled through the potentiometer on the front panel.
• The READING output monitors the input signal after the input and filter stage.
• The MAIN CHANNEL and ALT CHANNEL connectors provide the normalized, but
unweighted input signals.
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Output Section
The A2/A2-D is equipped with a versatile digital generator, providing optimum performance
with maximum flexibility to supply the device under test with purest signals.
The most important features of the generator are
• Output level -100dBV to +27.6dBV (10µV-24.5V
• Frequency range 10Hz-100kHz
• Selectable output impedances <15Ω to 600Ω
• Seven different signal waveforms
Very pure sine signal with typical THD+N < -91dB (<0.001%)
Warbled sine signal
IMD signal according to SMPTE and DIN
Squarewave (duty cycle 50/50 or 40/60)
W&F signal according to IEC and NAB
White noise
Pink noise
• Fast parameter setup through function keys and softwheels
• Individual mute function for each channel
• Sweep capability over the entire frequency & level range
Output Circuit
The diagram below shows the simplified diagram of the A2 output stage.
RMS
)
Fig. 7 Generator Block Diagram
All output signals are generated by the internal Digital Signal Processor of the A2/A2-D. In
order to isolate the generator from the analyzer circuitry, optocouplers were inserted between
the DSP output and the D/A converter. The analog signal is filtered and fed into the balanced
output amplifier. Behind this stage, an attenuator selects the level range of the output signal.
The signal is then split to the two output channels and fed through the mute relays. The output impedances are wired behind these mute relays.
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Fig. 8 Output Wiring
Pin 1 of each XLR output connector represents the center potential between pin 2 (+signal)
and pin 3 (-signal). It can either be kept floating or be connected to the chassis ground . In
general, it is recommended to operate the A2/A2-D in the FLOATING mode in order to avoid
ground loops.
The <FLOATING / GND> switch is located on the rear panel of
the A2/A2-D.
• FLOATING disconnects pin 1 from chassis ground, i.e. the
reference potential of the output amplifiers is floating.
• GND links the reference potential of the output amplifiers
to chassis ground.
Balanced Operation
Normally, the A2/A2-D is operated in the balanced (symmetric) mode. In this case, the device
under test (DUT) is connected to the two hot pins 2 (+signal) and 3 (-signal) of the generator
output stage.
NOTE If working with a balanced load, it is recommended to operate the unit in
the FLOATING mode.
Unbalanced Operation
When driving an unbalanced device, it is recommended to connect pin 2 (+signal) of the output stage to the hot input connector of the DUT, and to link pin 3 (-signal) of the output stage
with the ground of the DUT. In this case, operate the A2/A2-D in the FLOATING mode. By
this way only, the loss of half of the output level can be avoided.
On the other hand, unbalanced loads may also be connected between pin 2 (or pin 3) and
pin 1 of the A2/A2-D output stage (half side connection). In this mode, it is recommended to
set the switch on the rear panel to GND in order to get an invariant reference potential.
Optional Transformer Output Stage
Some applications require a complete galvanic separation between the generator output
connectors and the device under test. For this purpose, a transformer option is available (article code AO7), that adds a high quality Audio transformer behind the power amplifier of the
A2/A2-D.
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The A2/A2-D generator specifications as well as the output impedance circuitry are the same
with and without the transformer option. Please refer to chapter 8. Instrument Setup for further
details.
Output Settings
The METER display mode provides the best overview on the generator settings and measurement results. Therefore, it is recommended to enter this mode when reading through this
chapter.
Output Parameters
The generator frequency, output level,
waveform and output impedance are
continuously displayed on the upper
two lines of the LC display.
The top line shows in large characters the set generator frequency and level. In the second
line, the selected output impedance and waveform are indicated, as well the actual output
voltage (readback value) or the input impedance of the device under test (please refer to
chapter Readback for more detailed information).
Signal Waveform
The <GEN SIGNAL> key allows to select the signal waveform to be generated. It will have
either the ~ (sine) or the ALT symbol illuminated from behind by a green LED. To toggle the
setting, simply push the button once.
• In the ~ mode, the generator output will be a
pure sine signal.
• In the ALT mode, the actually selected alter-
nate signal is active.
The A2/A2-D digital generator offers a wide range of alternate signals. To make one of them
the active signal, double-click on the <GEN SIGNAL> key. This opens the Alt Signal menu,
showing the list of available alternate signals.
The active signal is displayed inverted (white characters on a
black background). To change the selection, move the arrow
on the left-hand side through the <SCALE> softwheel to the
alternate signal you wish to select and press the <SCALE>
wheel once.
Consequently, the actual selection of the alternate signal will
change accordingly, i.e. the new signal will become active, and
the menu will close automatically.
Alternatively, selection of the EXIT entry or any keypress to the
A2/A2-D keyboard will leave the menu without a change of the
actual setting.
NOTE In some measurement functions like IMD and W&F, a predefined wave-
form - depending on the selected standard - is activated as alternate signal.
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Therefore, activation of the "Alt. Signal" menu will show this setting. Al-
though it is possible in this state to alter the signal in the menu, it will be
re-set automatically to the predefined waveform as soon as the menu is
closed.
Square Signal (Sym. / Asym.)
The Square Sym. and Square Asym. are squarewave signals with either a duty cycle of
50/50 (sym) or 40/60 (asym). Regardless of the duty cycle, the squarewave signal has the
actually selected frequency and level, calibrated in true V
A typical application for the 40/60 signal may be for quickly checking the polarity of lines.
RMS
.
IMD TestSig
The IMD test signal consists of two signals components,
• a sinewave with a fixed frequency of 60Hz or 250Hz, and
• a second sinewave with a frequency of at least 4kHz, that may be set through the
<FREQUENCY> softwheel.
Fig. 9 IMD Testsignal
The level ratio between the low- and the high-frequency component is either 1:1, 4:1 or 10:1
(refer to chapter 5. Measurement Functions). Consequently, there are six different IMD test
signals available (according to the SMPTE and DIN standards). To define one of them as
default signal, the IMD Default menu must be opened by a double-click on the <IMD> key.
In normal operation, the IMD TestSig will be activated automatically as soon as the IMD
measurement function has been entered. Alternatively, it may also be activated manually
through the Alt. Signal menu.
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