Nagra III Instructions For Use Manual

M

ay

1st

1963

INSTRUCTIONS

MANUAL

KUDELSKI

6,

ch. de

,1'Etang,

Paudex - Lausanne, Switzerland

Office-hours

7.

30 -12.00

a. m.

and 1.30

- 6.

00

p. m.

(salurday closed)

Phon

e

Lausanne

(021) 28

6262

Te

le

x

Swilzerland

24 392

,

Playb8ck

Head

R_rdlhad

Accelerator

Function

19.

21.

Neopilot

Head

for

Motion

Pic·

tu

....

Product.

20.

24.

1.

Feed

Spool

Speed

and

Shoulder

Modulation

Tape

equalization

Select. Switch

Strap

Button

Level

Meter

22.

3.

Bra

..

Head

Microphone

Tension

Battery

Microphone

Input

Pilot

Signal

Flutter

Level

Control

Indicator

Filters

8.

9.

Tak

..

Up

Spool

25.

T_lon

Pulley

PlnchW

.....

17.

Une

Input

and

Playback

Volume

Control

1

••

13.

Reference

MonitOring

5.

16.

Tape

Tranaport

Control

Input·

Pulley

Indicator

Button

Selector

Switch

Signal

Button

Output

Socke

..

I

j

r-

5'

ID

:;

'tJ

C

....

IJI

QI

ii'

:2

n

ID

Q.

o

C

....

'tJ

C

..

NAGRA

III

TAPE

RECORDER

INSTR

UCTIONS

FOR

USE

1.

PRECAUTIONS

TO BE

TAKEN

When

out

of

use,

turn

the

tape

transport

control

to

its

mid

position.

In

the

"ON"

position,

when

not

running,

there

is

danger

of

producing a flat

on

the

capstan

roller. The

working

surfaces

of

the

fast

rewind

clutch

may

also

suffer.

II

When

batteries

are

exhausted, a corrosive

liquid

may

escape

and

the

containers

may

corrode.

Never

leave

discharged

batteries

in

the

Nagra.

If

the

machine

will

not

be

used

for

sometime

(a

few

months),

remove

the

batteries,

even

if

they

are

not

discharged,

as a precaution.

Take

care

that

the

batteries

are

inserted

into

the

machine

with

correct

polarity.

Place

them

in

the

battery

compartment

as

indicated

by

the

small

diagram

on

the

bottom

of

the

compartment.

When

an

external

power

supply

is

used,

always

check

the

polarity

very

carefully.

If

it

is

incorrect,

the

motor

will

run

backwards.

A

special

protective

circuit

is

used

to

prevent

damage

to

important

parts

of

the

Nagra,

but

even

so

it

is

possible

that

some

electrolytic

co

ndensers

could

be

damaged.

The

Nagra

III

is

very

robust,

but

it

is

better

to

take

no

chance.

Protect

it

from

sand,

sea,

being

dropped,

or

from

mechanical

shock.

Do

not

subject

it

to

rapid

changes

of

temperature,

or

to

the

curiosity

of

unqualified

personnel,

and

above

all,

from

vibration.

For

instance,

do

not

carry

it

unprotected

in

the

baggage

compartment

of a car.

II.

DESCRIPTION

OF

CONTROLS

AND

EXTERNAL

MECHANISM

1.

Speed

and

Equalization

Selector.

This

switch

may

be

operated

by a coin

in

the

slot.

It

Simultaneously

changes

speed

and

equalization,

both

for

recording

and

play-

back.

The

following

combinations

are

available:

38,1

cm/sec.

=

15"/sec.

(CCIR

or

Ampex)

This

speed

is

normally

used

in

broadcasting

studios.

The

use

of

it,

insured

the

best

quality;

the

azimuth

adjustmen~

is

not

very

critical,

while

the

response

Page

2

curve

is

always

excellent

and

varies

little

from

tape

to

tape.

At

this

speed

the

tape

is

little

affected

by

repeated

play-backs.

Another

advantage

is

that

editing

is

easy,

and

that a suitable

machine

operating

at

this

speed

can

usually

be

found

in

studios

for

play-

back

of

recordings.

19,05

cm/sec.

==

7.

5"/sec.

CCIR

Equalization

Standard

This

is

the

normal

speed

for

the

general

uses

of

the

Nagra

in

studios

working

with

the

CCIR

standards.

Where

this

is

not

necessary,

the

following

position

will

be

preferred:

19,05

cm/sec.

==

7.5"/sec.

Ampex

Equalization

Standard

This

is a better

standard,

as

the

modulation

noise,

medium

range

distortions

and

tape

backgr'ound

noise

are

reduced

considerably.

9,525

cm/sec.

=

3.75"/sec.

This

speed

is

for

use

where

high

quality

is

not

required

and

tape

economy

is

important.

One

hour

recording

time

can

be

obtained

with

the

use

of

5

11

reels

and

using

extra

thin

tape

or

two

hour's

with

7"

reels.

2)

Tension

Pulley

This

pulley

is

movable

and

operates a brake

on

the

spool,

ensuring

constant

tape

tension.

3)

Microphone

Input

The

microphone

should

have

an

impedance

of

50

or

200

ohms.

This

input

socket

on

the

Nagra

is

Cannon

type

XLR

3-42.

The

plug

on

the

microphone

cable

is

Cannon

type

XLR

3-11C.

Contact

No.1

is

earth

and 2 and 3 are

the

microphone

connections.

The

input

is

symmetrical

and

floating,

there

being

no

connection

between

primary

and

earth.

4)

Shoulder

Strap

Button

For

the

attachment

of a shoulder

strap

or

ever

ready

case a small

set

screw

is

fitted

for

safety

in

the

nut

(3

mm.

Set

screw, for

Allen

key

to

DIN

913: a key

0.050"

(1.

27

mm)

is

provided).

5)

Modulation

Level

Meter

The

upper

scale

on

the

meter

is

for

measuring

the

input

level

(on

Test

or

on

Record),

and

the

output

level

to

the

line

on

Hi-Fi

play-back.

Normally

the

pointer

will

not

reach

the

black

segment

between 0 and

+2db,

which

is

the

region

of

over

modulation.

The

recorder

has a safety

factor

of

about 6 db,

so

that

an

occasional

accidental

incursion

into

this

region

is

of

no

consequence.

The

level

control

should

be

adjusted

so

that

the

pointer

only

reaches

the

black

zone

on

the

loudest

parts

of

the

recording.

6)

Battery

Indicator

The

lower

scale

of

the

meter

is

for

checking

the

state

of

the

batteries.

The

meter

is

connected

to

the

batteries

when

the

selector

switch

indicates

"Play-

back

and

Batteries

Meter",

that

is,

when

playing

back

on

the

internal

loud-

speaker.

The

pointer

should

lie

in

the

marked

segment

when

the

batteries

are

in

working

condition.

This

indication

leaves a good

factor

of

safety

when

Page

3

employing

this

speed,

headphones

should

be

used

for

monitoring.

Then

when

the

battery

voltage

falls

to a level

unsatisfactory

for

recording

an

alarm

signal

will

be

heard

in

the

phones.

It

is

well

to

remember

..that

batteries

used

uninterruptedly

for,

say,

an

hour,

will

recuperate

when

rested

for,

say,

10

hours.

Therefore

exhausted

batteries

may

appear

acceptable

during a quick

test

before

recording,

but

then

collapse

after a few

minutes

use.

To

recapitulate:

If

one

is

recording

at

15" / sec.

always

use

monitoring

headphones

and

read

the

battery

meter

pessimistically.

If

one

is

recording

at

7

1

/2"

or 3 3/4

11

/sec . for

fairly

short

periods,

say

15

minutes, a battery

test

before

starting

should

be

sufficient.

On

the

other

hand,

if

the

recording

s e

ssion

is

of

long

duration,

the

batteries

should

be

checked

when

changing

reels.

7)

Pilot

Signal

Indicator

This

is

an

indicator

on

which a white

cross

will

appear

when

the

Nagra

is

receiving

the

pilot

signal

(N eopilot

Nagras

only).

8)

Accelerator

Button

By

pressing

this

button

the

motor

speed

is

increased

to

its

maximum.

This

can

be

done

during

play-back

for

forward

spooling.

Although

no

damage

will

be

done

by

pressing

the

button

during

recording,

the

speed

will

be

incorrect.

9)

Function

Selector

Switch

This

switch

controls

the

functioning

of

the

Nagra.

It

has

two

sets

of

six

positions.

One

set

is

for

working

on

internal

batteries

when

the

end

of

the

switch

knob

marked

"bat"

is

used

as

an

indicator,

and

one

set

is

for

working

with

an

external

power

supply,

when

the

other

end

of

the

knob,

marked

II

ex

t",

is

used

as

an

indicator.

The

positions

are

as

follows:

STOP

in

the

centre

TESTING

to

the

right

In

this

position

the

amplifiers

are

connected

but

not

the

motor,

so

that

the

incoming

signal

to

be

recorded

can

be

checked.

The

monitoring

phones

are

connected

to

the

record

amplifier.

HI-FI

RECORD

=

Normal

recording

position.

The

phones

are

connected

to

the

play-back

amplifier,

so

that

the

actual

recording

that

has

been

made

is

monitored.

Incoming

signals

can

be

mixed

from

both

microphone

and

line

inputs.

The

level

of

each

of

these

signals

can

be

adjusted

by

the

appropriate

volume

controls.

If

the

line

input

is

only

used,

the

microphone

level

potentiometer

should

be

turned

fully

anticlockwise

to

prevent

the

recording

of

noise

from

the

microphone

pre-

amplifier.

On

the

other

hand,

if a recording

is

made

through

the

microphone

channel

only,

the

position

of

the

line

input

volume

control

is

immaterial.

AUTOMATIC

RECORD

=

Recording

with

automatic

control

of

level

and

attenuation

of

low

frequencies.

It

is

not

necessary

to

adjust

the

level

potentiometer

but

the

quality

of

the

recording

is

not

as

good

as

in

the

position

HI-FI

RECORD.

Page

4

The

automatic

record

position

is

useable

for

speech

but

not

for

music.

The

automatic

facility

only

affects

the

microphone

channel

and

not

the

line

input.
PLAYBACK & BATT.

METER

to

the

left = Play-back

on

the

internal

loudspeaker.

In

this

position

the

meter

indicates

the

battery

voltage.

The

play-back

level

is

varied

by

the

"line

input

and

playback"

volume

control.

The

headphones

are

fed

directly

from

the

play-

back

amplifier

at

an

uncontrolled

level.

The

quality

through

the

loudspeaker

or

at

the

line

output

is

not

high.

On

the

other

hand

the

monitoring

output

for

headphones

is

always

fed

with a high

quality

signal.

HI-FI

PLAYBACK

=

Normal

high

quality

play-back.

The

loudspeaker

is

out

of

circuit

and

the

signal

output

is

fed

at

low

level

for

headphones

at

the

monitoring

output

and

at

high

level

to

the

line

output

sockets.

The

signal

fed

into

the

line

is

measured

by

the

meter.

This

output

consists

not

only

of

the

signal

play-back

from

the

tape

and

adjusted

by

the

control

"line

input

and

play-

back"

but

also a signal

from

the

microphone

can

be

added

for a commentary.

The

level

of

this

signal

is

controlled

by

the

mike

input

potentiometer.

When

this

facility

is

not

required

the

mike

input

potentiometer

must

be

turned

fully

anticlockwise

when

replaying a normally

recorded

tape.

To

play

back a normally

recorded

tape,

the

"line

input

and

play-

backll

control

should

be

turned

to

the

indication 0 db.

This

will

produce a normal

signal

to

the

line.

If

it

is

necessary

to

vary

this

control

to

have a normal

signal

to

the

line,

it

is

an

indication

that

the

recording

has

not

been

made

at

normal

level.

This

is a useful

facility

for

checking a recording.

10)

Microphone

Input

Level

Control

This

control

varies

the

modulation

level

of

the

signal,

which

is

fed

into

the

microphone

input.

11)

Zero

Level

Reference

Signal

Push

Button

This

push

button,

sends a whistle

through

the

line

input

while

the

recorder

is

running.

It

is

useful

to

record

this

whistle

before

recording

sound

at

a

zero

level,

that

is

to

say,

the

modulometer

needle

should

point

to

zero

on

the

scale.

This

signal

is

highly

useful

for

the

regulation

of

the

chain

of

sound

transfer.

It

is

as

well

to

leave

at

least

two

complete

turns

of

the

tape

between

the

signal

and

the

sound

track

so

as

to

avoid

the

possibility

that

it

might

be

superimposed

on

the

sound

track

during

the

transfer

process.

12)

Line

Input

and

Play-back

Volume

Control

This

control

has

two

purposes:

a)

During

Hi-

Fi

recording

it

varies

the

modulation

level

of

the

signal

fed

into

line

input.

b)

During

play-

back

it

varies

the

signal

output.

13)

Monitoring

Output

Sockets

These

sockets

are

suitable

for

headphones,

with

an

optimum

impedance

of

50

ohms.

Any

other

impedance

value

will

only

result

in a reduced

level.

It

is

preferable

to

use

electrodynamic

headphones

of

high

quality.

In

operation

this

output

is

taken

from:

Page

5

The

recording

amplifier

when

on

IITestingl1

The

play-back

amplifier

on

"Record"

"Automatic

Record"

and

"Play-back

and

Batt.

Meter

" .

The

line

amplifier

on

"Hi-Fi

Play-back"

The

normal

output

level

is

approximately

250

mY.

One

can

use

this

output

to

connect

the

Nagra

to

an

external

power

amplifier.

A 1

arm

S i g n a 1 .

This

signal

is

injected

between

the

lower

socket

of

the

monitoring

output

and

earth,

when

the

motor

speed

stabiliser

reaches

the

bottom

of

its

range,

that

is,

during

fast

rewind

and

in

case

of

exhaustion

of

batteries

or

accidental

braking

of

the

motor.

If

one

uses

this

output

for

connection

to a power

amplifier,

the

alarm

signal

can

be

quite

annoying.

In

order

to

avoid

this,

one

connects

the

external

amplifier

between

the

earth

on

the

line

input

on

the

right

side

of

the

apparatus,

and

the

upper

socket

of

the

monitoring

output.

14)

a.

Line

Input

This

input

is

at

high

impedance

and

one

can

connect

it,

for

instance,

to a radio

receiver

to

record a transmission.

The

input

impedance

is

100.000

ohms

and

the

normal

level

0,

5

volt.

b,

Accessory

Socket

The

corresponding

plug

is a Tuchel

T.

3400.

The

connections

are

shown

on

the

surrounding

label

as

follows:

1.

o

Batteries

taken

direct

to

the

negative

of

the

internal

battery.

This

can

b p

used

for

recharging

internal

accum

ulators

if

they

are

employed

in

place

of

batteries.

2.

o

Earth

=

the

positive

of

the

battery

is

connected

to

earth.

3.

o

Line

This

line

input

is

similar

to

the

line

input

mentioned

above

but

the

impedance

is

2500

ohms

and

the

normal

level 8 mY.

This

is

for

use

with

the

Nagra accessories

such

as

external

m

ic

rophone pr

earn

plifie r.

4.

o

Stop

connection

for

remote

control -if

reconnected

to

earth

the

motor

will

stop.

5.

o

External

=

This

is

the

connection

for

the

negative

of

an

external

power

supply.

The applied

voltage

should

be

between

12

and

24

volts

DC

and

must

not

exceed

25

volts.

6.

o

-10.5V

regulated

voltage

for

supply

of

accessories.

c)

Balanced

Output

This

line

output

is

symmetrical

and

floating.

The

characteristics

are

marked

on

the

label:

with a load

not

less

than

600

ohms

4,

4 V

(+

15

db)

0 r

" "

" "

"

100

ohms

1,55

V

(+

6

db)

a

At

this

socket

the

following

signals

will

be

found:

During

testing

and

recording.

the

signal

applied

to

the

recording

head.

One

should

not

load

these

sockets

during

this

operation.

(Except

when a DH

amplifier

is

used).

During

Play-

back & Batt.

Meter

the

signal

feeding

the

with

reduced

reserve

of

the

level.

Page

6

Do

not

use

this

position

for

high

quality

feed

to

another

unit.

During

Hi-

Fi

Play-

back

these

sockets

carry

the

normal

line

output

signal.

15)

Tension

Pulley

This

pulley

is

movable

and

controls

the

take-up

spool

clutch.

The

normal

tape

tensions

are

given

in

the

speGification

of

the

instrument.

16)

Tape

Transport

Control

Turning

this

control

which

is

marked

on

one

side

IIEn_Onlt

clockwise,

brings

the

pinch

wheel

into

contact

with

the

capstan.

Turning

it

to

the

left

disengages

it,

and

starts

rapid

tape

rewinding.

This

occurs

when

the

selector

switch

(No.9)

is

turned

to

either

play-back

position,

rewinding

does

not

take

place

when

the

switch

is

on

Ilrecordlt,

to

diminish

the

possibility

of

mistakes.

If

re-

spooling

is

required

when

the

switch

is

at

ItTestinglt

this

can

be

obtained

by

depressing

the

accelerator

button

(No.8).

When

the

equipment

is

not

in

use,

this

control

must

be

left

in

the

mid

position.

(See

page

1).

17)

Pinch

Wheel

This

rubber

roller

presses

the

tape

against

the

capstan

to

drive

the

tape.

It

is

operated

by

the

control

mentioned

above

(No.

16)

The

pressure

of

the

pinch

wheel

can

be

adjusted

by

means

of a screw

on

the

assembly.

(1

kg

optimal).

'

18)

Capstan

This

drives

the

tape

at a constant

speed.

19)

Play-back

Head

20)

Neopilot

Head

21)

Record

Head

22)

Erase

Head

23)

Flutter

Filters

These

carry

markings

which

enable

the

tape

speed

to

be

checked

strobosco-

pically.

When

lightened

by a pulsed

light

source

(e.

g.

from

an

electric

lamp,

preferably

fluorescent,

supplied

from

50

or

60

c.

p.

s.

mains)

they

give

the

impression

of

being

stationary,

if

the

tape

speed

is

exactly

correct.

On

the

other

hand,

if

the

dots

appear

to

turn

slowly

clockwise,

the

speed

is

too

great,

and

conversely.

The

number

engraved

on

the

top

of

the

guide

gives

the

mains

frequency

for

the

correct

speed.

To

appreciate

the

magnitude

of

error

of

speed,

at

50

c.

p.

s. a movement

of

one

dot

over a distance

equal

to

the

separation

between

dots

in

one

second

indicates

an

error

of

1%.

If

the

time

taken

is

ten

seconds,

the

error

is

0,

1

%.

It

must

be

taken

in

account

that

the

mains

stability

Page

7

is

not

perfect.

Variations

of

0,5%

are

quite

common.

The

speeds

are

set

at

the

factory

by

comparison

with a standard

generator

driven

from a Quartz

crystal

clock.

Therefore

the

speed

should

not

be

readjusted

if

the

mains

frequency

is

not

known

to

be

accurate.

24)

Feed

Spool

The

tape

to

be

recorded

or

reproduced

is

placed

on

this

spool,

with

the

coating

(matte

surface)

wound

inwards.

25)

Take

Up

Spool

The

Battery

Box

compartment

is

accessible

from

the

bottom

of

the

instrument.

A

normal

set

of

batteries

consists

of

12

1.5

volt

torch

cells.

When

changing

cells,

all

should

be

changed

together,

as

one

inferior

cell

will

substract

from

the

performance of

the

good

ones.

It

is

very

important

not

to

make

any

mistake

over

the

polarity

of

the

batteries,

all

should

be

turned

in

the

same

direction

as

indicated

by

the

diagram

on

the

bottom

of

the

box

.

It

is

more

convenient

to

put

the

end

cells

in

place

first,

and

then

the

centre

cells.

The

minimum

voltage

below

which a cell

cannot

be

used

is

0.9

volt.

Usable

battery

types

are:

1)

Alkaline

cells

such

as

ever-ready

E95

(life

about

70

hours).

2)

Ordinary

torch

dry

cells,

(diam.

33

mm,

length

60

mm)

(life

about

10

to

20

hours).

U.S.A.

Ever-ready

950

D,

R.

C.

A.

VS.

036

Ray -O-Vac 2 LP,

Burgess

2D,

Usalite

879

England

Vidor V 0002,

Berec

U 2

Germany

Titania

2211

France

Wonder

I!Marin

rr

1602,

Mazda

(Cipel)

RGT

1,5V

Spain

Hellesens

211

Switzerland

Leclanche

300

ou

300

S

Pakistan

Alladin

1, 5 V

cell

India

Ever-

ready

1 F 3

China

Pile

Elephant

1, 5 V

Hongkong

Kai-it

360

Italy

Super

Pila

No.

60

It

is

desirable

to

use

the

steel

clad

type

of

cell,

with

silvered

contacts,

to

avoid

trouble

due

to

corrosion

and

bad

contacts.

3)

Sealed

Accumulators.

These

are

rechargeable.

It

is

often

possible

to

recharge

these

400

times,

although

the

manufacturer

does

not

guarantee

more

than

100

rechargings.

They

have

the

disadvantage

of a very

constant

output

voltage

so

that

it

is

very

difficult

to

estimate

the

amount

of

charge

remaining.

Their

capacity

is

comparable

to

that

of

ordinary

cells,

but

they

are

heavier,

increasing

the

total

weight

of

the

Nagra

by

about 1 lb. 3 ozs.

Switzerland

Leclanche

32

A

Germany

DEAC

2,5

Ah

U.S.A.

Gould

2,5

Ah

Page

8

THE

SPEED

STABILISER

The

Nagra

III

uses a new

technique

for

controlling

the

speed

of

the

motor

and

the

following

notes

will

be

helpful

to

those

who

need

to

service

the

machine.

1.

Description

The

block

diagram

herewith

illustrates

the

principle

of

the

servo-

circuit

which

is

used.

The

motor

carries

on

its

spindle a phonic

wheel

as

well

as

the

capstan,

which

passes

in

front

of a magnetic

head -the

tachometer

head.

This

head

is

magnetised

and

the

rotation

of

the

phonic

wheel

induces

an

alternating

current,

the

frequency

of

which

depends

upon

the

speed

of

rotation

of

the

motor.

This

signal

passes

through

the

tachometer

amplifier

where

it

is

shaped

into a square

wave

of

constant

amplitude

of

about 6 volts

peak

to

peak.

This

output

is

taken

to a frequency

discriminator.

This

operates

the

servo

a

mplifier

which

controls

the

motor

speed.

As

the

voltage

at

the

servo

amplifier

becomes

increasingly

negative,

so

the

motor

current

will

increase

.

The

circuit

described

is

not

self-starting.

Therefore

the

Nagra

includes

a

starter

which

applies

to

the

servo

amplifier a large

negative

voltage

when

one

switches

to

"play-back"

from

"stop"

or

from

"test"

to

"record",

and

also

when

the

connection

between

the

socket"

stop"

on

14b

and

earth

is

opened.

This

applied

voltage

causes

the

motor

to

start

rapidly.

The

system

could

function

just

in

this

way,

the

discriminator

being

sufficiently

powerful

to

intercept

and

take

the

motor

under

control

as

the

speed

passes

intothe

range

of

the

discriminator.

However,

the

speed

would

not

be

correct

immediately.

It

would

be

above

normal

for

several

seconds,

that

is,

for

the

time

necessary

for

the

starting

condenser

to

discharge.

To

overcome

this

difficulty a special

transistor

discharges

the

condenser

when

the

circuit

of

the

discriminator

begins

to

resonate.

This

gives

excellent

starting.

At

all

times

a

precaution

must

still

be

taken,

the

signal

coming

from

the

tachometer

amplifier

is a square

wave,

that

is,

it

contains

about

300/0

of

third

harmonic.

Put

another

way,

during

the

passage

at

1/5

and

above

all

at

1/3

of

the

speed,

the

circuit

of

the

discriminator

could

resonate

and

the

starting

condenser

will

be

discharged.

We

inserted a threshold

diode, visible

on

the

diagram,

to

avoid

any

discharge

for a signal

of

less

than

500/0.

Notice

that

the

accelerator

button

works

directly

on

the

motor

while

the

rapid

rewind

works

through

the

servo

amplifier.

This

can

help

in

localizing a fault.

Remember

that

the

rewind

circuit

is

disconnected

when

the

selector

switch

is

on

"record".

II.

Possible

Difficulties:

1)

Faults

in

starting

a)

The

motor

refuses

to

run

even

after

pressing

the

accelerator

button

or

starting

it

by

hand.

Check

the

tension

of

the

brushes

and

examine

the

commutator.

Page

9

b)

The

motor

starts

occasionally

but

not

always,

or

on

turning

by

hand.

The

commutator

may

be

dirty,

clean

it

but

do

not

lubricate

it.

c)

The

motor

starts

after

pressing

accelerator

button

and

comes

up

to

speed,

but

does

not

start

on

its

own.

Fault

in

starter. Measure

the

voltage

ac

ross

the

starting

condenser.

d)

The

motor

starts

well,

passes

the

normal spe

ed

and

then

loses

speed

and

stops.

This

is a typical

case

where

the

servo

amplifier

and

the

starter

are

functioning,

but

the

discriminator

or

the

tachometer

head

is

not

working.

Start

the

motor

with

the

accelerator

button

with

a

driving

voltage

of

10

to

15

volts.

The

tachometer

head

should

develop

more

than 8 millivolts.

If

the

head

is

in

good

condition

inject a signal

of 3 millivolts

from a low

frequency

source

corresponding

to

the

speed

of

working.

This

will

permit

tracing

the

signal

through

the

tachometer

amplifier.

In

case

of

trouble

of

this

sort

it

is

good

to

try

straight

away

whether

operation

is

satisfactory

on

other

speeds.

It

is

at 3 3/4"

per

s e

cond

that

one

has

most

difficulty

because

of a weak

tachometer

signal.

If

operation

is

satisfactory

at 3 3/4",

but

not

at

any

other

speed,

examine carefully

the

wires

joining

the

speed

switch

to

the

speed

regulating

inductances

etc

.

e)

The

motor

starts

but

does

not

reach

normal

speed.

Disconnect

the

collector

of

the

transistor

T. 4 which

discharges

the

starter

condenser

and

so

ascertain

whether

this

transistor

is

discharging the

condenser

too

soon

or

whether

the

charge

on

the

condenser

is t oo

sm all,

that

is

to

say,

whether

the

motor

is

too

difficult

to

start.

One

can

then

determine

whether

the

motor

is

half

open

circuit

and

needs

too

much

voltage

or

if

the

supply

is

incapable

of

producing

the

necessary

voltage

or

whether

there

is

untoward

mechanical

friction

or a faulty

servo

amplifier.

On

replacing

the

motor

by a milliameter,

there

would

be a starting

current

of

at

least

400

milliamps

flowing,

for

more

than

one

second.

Measure

the

voltage

across

the

last

transistor

in

the

servo

amplifier.

If

all

the

applied

voltage

reaches

the

motor,

without

being

able

to

reach

its

full

speed

..........

.

conclusion

ob'

Lous.

On

the

other

hand,

if

the

disconnection

of

the

discharging

transistor

T. 4 makes

starting

possible,

check

whether

the

stand

off

voltage

is

accurately

applied

and

that

the

transistor

T. 4 is

in

good

condition.

At 3 3/4

i.

p.

s.

the

discharging

signal

being

smaller

the

stand

off

is

not

necessary.

Also

the

tachometer

amplifier

does

not

amplify

the

frequency

1000/3

sufficientl y for

dipping.

f)

The

motor

starts

correctly

but

passes

through

normal

speed

and

then

returns

to

normal.

This

shows

that

the

starter

discharger

is

not

functioning

or

functioning

insufficiently.

Its

voltage

should

be

measured

and

compared

with

the

schematic.

(Check

the

diode).

2)

Faults

of

Control

Typical

Case:

When

the

accelerator

is

depressed

the

motor

speeds

up

but

when

the

button

is

released

the

speed

of

the

motor

does

not

fall

to

normal.

This

fault

is

particularly

obvious

when

there

is

no

tape

in

the

machine.

Page

10

Cause:

The

servo-

amplifier

passes

current

to

the

motor

even

when

the

discriminator

does

not

call

for

it.

This

is

generally

caused

by

thermal

current

in

the

transistors.

This

trouble

will

arise

on

every

equipment

if

the

ambient

temperature

is

sufficiently

high.

It

is

abnormal

below

400 centi-

grade.

Two

possibilities

must

be

considered:

Cl)

The

motor

has

an

abnormally

high

consumption

which

heats

the

servo

amplifier.

(See

"Faults

in

Motors").

b)

One

or

more

transistors

of

the

servo

amplifier

have

deteriorated

(by

over-

heating,

for

exampl'e)

and

their

standing

current

has

becom

e

too

high.

Change

these

components,

being

careful

not

to

over-heat

when

soldering.

This

fault

will

disappear

when

one

short

circuits

to

earth

the

bases

of

the

suspected

transistors.

Each

transistor

base

is

connected

to

earth

by a resistance.

The

disconnection

of

such

resistances

is

sufficient

to

increase

the

fault. A resistance

of

this

type

is

also

contained

in

the

discriminator.

3)

Wow

and

Flutter

a)

Wow

at

the

frequency

of

rotation

of

the

capstan.

Possible

source:

Mechanical

or

electrical

braking

on

the

motor

(see

"faults

in
motors").
The

tachometer

wheel

is

eccentric

glVIng a signal

of

which

the

amplitude

varies

more

than

30%.

The

limiting

amplifier

can

change

this

amplitude

modulation

into a phase

modulation

of

the

square

wave.

Such

modulation

will

"mislead"

the

discriminator.

Tachometer

wheel

magnetised:

This

induces

into

the

tachometer

head a strong

signal

of

very

low

frequency

which

passes

through

the

tachometer

amplifier

and

upsets

the

discriminator.

Demagnetise

the

wheel.

When

one

has

sufficient

and

suitable

equipment,

this

type

of

fault

is

very

easy

to

localize.

It

is

necessary

to

find

out

first

whether

the

speed

stabiliser

is

not

able

to

compensate

for a fault

in

the

motor,

or

on

the

contrary,

if

it

is

the

stabiliser

which

provokes

the

wow,

having

been

upset

by

an

incorrect

voltage

from

the

tachometer

circuit.

b)

Irregular

Wow

The

most

likely

cause

is

slipping

of

the

tape.

Try

re-tensioning

the

pinch

wheel. A pressure

of

one

k.

gram

should

give

satisfactory

results;

Check

the

tension

of

the

tape

according

to

the

respective

instruction

sheet.

c)

Flutter

A

rapid

flutter

is

caused

by a break

in

the

servo-amplifier

feed-back

chain.

Too

much

feed-back

increases

the

wow

and

could

even

set

the

circuit

into

oscillation.

In

the

case

of

difficulty

with a recorder

of

the

first

series

modify

the

circuit

to

conform

with

the

new

schematic.

Page

11

MOTOR

The

motor

of

the

Nagra

is

of

the

permanent

magnet

electrodynamic

type

and

resembles

a d I

Arsonval

galvanometer

with

central

magnet.

It

may

be

the

cause

of a number

of

difficulties

and

the

following

notes

are

intended

to

assist

in

such

cases:

If

the

recorder

refuses

to

start

occasionally,

even

when

one

presses

the

accelerator

button,

but

in

general

starts

when

one

turns

it

lightly

by

hand,

the

surface

of

the

com

mutator

should

be

examined -see

paragraph

5 .

If

the

recorder

runs

irregularly,

see

paragraph 5 and

subsequently

paragraph

6.

If

the

recorder

produces a flutter,

check

the

smoothness

of

rotation

of

the

motor.

There

must

be

neither

rough

spots

nor

perceptible

play.

If

the

motor

shows

speed

up

following

excessive

heating

of

the

power

transistor

of

the

servo

amplifier,

see

first

paragraph

6,

then 4 and

3,

and

finally

1.

1.

Dismantling

and

de-magnetisation

The

magnet

is

fixed

in

the

assembly

by a left

hand

threaded

set

screw.

The

winding

surrounds

it.

To

remove

the

rotor,

after

first

having

unscrewed

the

centre

screw

(normal

right

and

thread),

it

is

necessary

to

introduce a rod

3

mm

in

diameter

into

the

hole

in

the

rotor

between

two

wires.

Turning

the

rotor,

if

necessary,

one

can

reach

with

the

rod

one

of

the

two

notches

in

the

magnet

and

so

unscrew

it.

This

gives

access

to

the

central

ball

race

of

the

assembly

(type

EL4ZZ).

This

ball

race

must

be

of

very

high

accuracy, much

superior

to

those

of

normal

commercial

type.

In

case

of

need,

ask

for

replacements.

In

taking

out

the

rotor,

it

is

essential

(unless

you

have a magnetising

machine

of

considerable

power

such

as

we

have)

to

short

circuit

the

magnetic

circuit,

otherwise

the

magnet

will

lose

about 25%

of

its

magnetism.

One

can

do

this

by

sliding

the

rotor

into

another

iron

tube

of

suitable

size

(internal

diameter

56

mm,

external

diameter

minimum

60

mm)

in

such a manner

that

the

magnetic

circuit

is

never

opened.

In

case

of

repairs

on

the

field,

one

obviously

cannot

take

this

precaution.

The

considerable

reserve

of

power

of

the

motor

ensures,

nevertheless

,

that

the

recorder

will

still

be

usable.

The

consumption

will

however

be

higher

and

rapid

rewinding

will

be

slower.

In

such

cases

it

is

necessary

to

return

the

rotor

to

us.

We

will

return

it

to

re -magnetised

and

in a short

circuiting

type

of

tube

from

which

it

can

be

slid

into

the

motor.

To

check

that

the

magnet

has

not

been

partially

de-magnetised

the

voltage

required

on

no

load

should

be

measured,

that

is,

without

tape

and

without

the

pinch

wheel

being

engaged,

at

15

i.

p.

s.

(600

r.

p.

m.) A motor

in

good

condition

requires

9 V ±

0.5

V. A motor

de-magnetised

by

dismantling

without a magnetic

short

circuit

will

need

only

7,5

volts.

Later

dismantlings

will

not

increase

the

amount

of

de-magnetisation.

Page

12

2.

Open

Circuit

of

Half

the

Rotor

Below

there

is a schematic

of

the

motor.

It

can

be

seen

that

the

current

passes

through

two

paths

in

parallel.

Interruption

of

one

of

the

paths

does

not

prevent

the

motor

from

functioning

but

doubles

its

resistance.

This

is

indicated

by

a

less

vigorous

rewind

and

partly

by

an

increase

of

the

limiting

voltage

required

for

operation

at

15

i.

p.

s.

One

localize

this

fault

by

measuring

of

the

rotor.

The

normal

value

is

21

ohm s but a rotor

half

open

circuited

will

read

42

ohms.

3.

Short

circuit

between

segments

A

short

circuit

between

two

segments

of

the

commutator

has

very

serious

repercussions;

wow

at

double

the

speed

of

rotation

of

the

capstan

and

increase

in

power consumption.

Such a short

circuit

can

happen

in

the

windings

or

inside

the

commutator, but

such

cases

are

less

likely

in

recorders

which

are

in

service.

On

the

other

hand,

it

is

much

more

likely

that a metallic

deposit

has

appeared

on

the

insulating

segments

of

the

commutator.

To

localize

this

kind

of

fault,

it

is

necessary

to

measure

the

resistance

between

adjacent

segments.

It

is

usually between 6 and 8 ohms

throughout

the

series.

It

increases

regularly

from

the

first

to

the

last

winding

progressiv ely

from 1 to

1,5

ohms

in

all.

Any

abnormally

low

resistance

found

here

indicates a fault.

First

of

all

the

commutator

should

be

cleaned

with a very

fine

emery

cloth,

then

washed

carefully

to

eliminate

Page

13

all

traces

of

abrasive

powder

.

If

lhe

fault

cuntinues,

the

corresponding

wire

of

the

coil

should

be

disconnected.

It

is

then

possible

to

ascertain

if

the

fault

is

in

the

winding

or

in

the

commutator

.

If

the

winding

has

short

circuited,

a

new

rotor

should

be

ordered

from

us.

On

the

other

hand,

it

is

often

possible

to

repair

the

commutator

by

passing a very

large

current

through

the

short

circuit

to

break

it

down.

The

discharge

of a 100

microfarad

condenser

charged

to

300 volts

will

generally

be

sufficient.

4.

Mechanical

Fnction

Mechanical

friction

of

the

rotor

increases

both

the

wow

and

the

power

taken.

One

can

distinguish

between

eleclric

braking,

such

as

is

shown

in

the

preceding

paragraph,

because

mechanical

friction

is

constant,

whereas

the

ele~tric

braking

increases

quickly

when

the

motor

speeds

up.

Typical

valuE's

of

the

consumption

of

the

motor

on

no

load,

that

is

without

tape

and

with

the

pinch

wheel

not

in

contact

with

the

capstan

(but

not

on

rapid

re~wind)

are

given

below:

Speed

Normal

no

load

current

No

load

current

with

two

segm

ents

short

circuited

15

i.p.s.

26

ma

62

ma

7 1/2

i.p.s.

20

ma

39

ma

33/4i.p.s.

17

rna

27

rna

5.

Dirty

Commutator

The

commutator

is

obviously

the

most

critical

part

of

the

motor.

It

is

designed

to

work

dry.

It

is

therefore

necessary

to

make

sure

that

the

commutator

is

perfectly dry.

It

can

be

cleaned

by

means

of a piece

of

rag

saturated

with a solvent

such

as

trichlorethyline

or,

better

still,

special

cleaning

fluid

.of

electrical

contacts.

Certain

of

these

products

leave

behind

a

very

thin

deposit

of

lubric

ant

which

seem s not

to

prevent

good

running.

6.

Misalignment

of

the

Axis

of

Commutation

This

axis

of

commutation,

that

is,

the

exact

position

of

the

brushes

with

respect

to

the

centre

magnet

is

very

critical.

A

misplacement

will

provoke

sparks

at

the

commutator

and

electrical

noise,

and a considerable

increase

in

current

consumed.

This

increase

may

be

sufficient

to

overheat

the

servo

amplifier

sufficiently

to

cause

irregular

running

of

the

motor.

Use

the

following

procedure

for

adj

usting

this

position:

Before

moving

the

brushes

mark

their

previous

position.

Start

the

motor

at

15

inches

per

second

m

~as

uring

the

current

taken.

The

correct

alignment

corresponds

to

minimum

consumption.

If

you

find a noticeable

difference

(more

than 5 mm

on

the

external

circumference

of

the

motor),

examine

the

fixing

of

the

magnet.

Page

14

A

misplacement

cannot

happen

except

by a previous

careless

service

work

or

by

unscrewing

or

dismantling

of

the

magnet.

The

left

end

thread

on

the

magnet

ensures

that

this

cannot

unscrew itself. On

the

other

hand,

it

can

happen

when

the

adjustment

mentioned

above

has

been

made

and

the

magnet

insufficiently

well

secured.

In

practice,

it

should

be

tightened

up

securely

before

re-adjustment.

If

the

difference

is

small,

replace

the

brushes

where

they

were

because

the

difference

is

probably

an

error

in

measurement.

Our

factory-adjustment

made

by

the

aid

of a special

machine

is

much

more

accurate

than

that

made

by

adjusting

to

minimum

current.

PRECA

UTIONS

AGAINST

INTERNAL

NOISE

As

with

all

tape

recorders,

the

Nagra

III

has

some

residual

noise.

We

must

distinguish:

1 ) NOLse

in

the

microphone

preamplifi

er

2) N

oise

in

the

record

amplifier

(output

amplifier)

3)

Noise

in

recording

on

the

magnetic

track

4)

Noise

in

the

play -back

amplifier

5)

Noise

in

the

switching

dlOdes

of

the

speed

standard

selector

6)

Noise

in

the

play-back

am

plifier

7)

For

the

second

time

noise

in

the

output

amplifier

Discussing

the

nature

of

these

noises,

we

have:

a)

Hiss

This

is

approx

imately white

noise,

that

is

to

say,

composed

of

all

frequencies

in the

spectrum.

It

resembles

the

noise

of a jet

of

air

or

dry

steam.

It

is

quite

clear

but a little

less

than

the

pronounciation

of

the

letter

"S".

Hiss

is

essentially

produced

by

thermal

agitation and

has a limiting

minimum

value

fixed

for a given

temperature

and a given

impedance.

Similarly,

the

noise

following

the

breakage

of a connection

on

the

input

circuit

is

of

this

type.

b)

Semiconductor

Noise

(Flicker

Noise)

This

is

similar

to

the

preceding

noise,

but

includes

more

low

frequencies.

Our

ears

are

always

less

sensitive

to

low

frequencies

at

low

level,

and

semiconductor

noise

is

distinguished

by

the

fact

that

it

is

modulated

by

these

loyv

frequencies.

The

sound

which

most

nearly describes

this

type

of

noise

is

that

of a jet

of

vapour

containing

drops

of

liquid,

for

example,

an

expresso

coffee

machine.

The

noise

is

produced

both

by

defective

resistances

carrying

continuous

current.

In

cases

1,2,

4,6

and 7 the

transistors

should

be

first

suspect,

then

the

base

dividing

resistances,

and

the

collector

resistances.

SPECIAL

WARNING

Do not

dismantle

your

Nagra

because

of

the

results

obtained

with a doubtful

tape. A bad

tape

can

produce

such

noise

on a perfect

machine.

c)

Residual

Noise

at

1000,

2000

and

4000

c.

p.

s.

The

speed

stabilisation

system

of

the

Nagra

uses

these

frequencies

and

it

can

happen

that

they

may

break

through

and

become

audible

at

the

speed

of 3 3/4"

per

second

which

we

do

not

consider"

professional".

A

perc

eptible

residual

signal

is allowed.

On

the

other

hand,

it

should

not

be

possible

to

hear

such

Page

15

residuals

during

recording

or

play-back

wlthout

signal

on til e

other

two

speeds.

The level in

general

will

be bettel'

thall -80

db.

Various

forms

of

break-through

are possible:

On

play-ba

ck

induction

between

the

motor

and

the

replay

head,

or

equally,

induction

be

tween

the

tachometer

head

and

the

wiring

to

the

replay

head.

A

re-routing

of

these

wires

may

reduce

the

trouble.

One

can

diagnose

thLs

trouble

by

short

circ1Jiting

the

wires

to

the

head

on

the

H.

F.

filter

on

the

chassis.

A

similar

fault

can

be

produced

by

damage

to

the

discriminator

filter

or

servo

amplifier.

It

is

normal

that

there

should

be

some

break

through

when

the

apparatus

is

working

with

the

chassis

opened.

On

record,

the

residual

signal

may

come

through

induction

into

the

microphone

preamplifier

and

cable

or

by

coupling

to

the

input

connection

of

the

power

amplifier

and

cable

or

finall

y,

through

the

power

leads

or

the

earth

leads.

These

residuals

are

adjusted

to

be

negligible

before

delivery

of

the

recorder.

Should

they a ppear,

it

is

likely

that a decoupling

has

deteriorated,

or a change

in

earthing,

or a misplacem

ent

of

the

connections.

d)

Electrostatic

Discharge

This

consists

of

short

sharp

cracklings

when

the

motor

is

in opera

tion,

at

irregular

intervals.

They

are

caus

ed

by

an

electrostatic

char

ge

on

the

belt.

A

little

brush

is

fitted

to

reduce

them.

This

brush

should

almost touch

the

belt.

In

cases

where

these

parasitic

noises

occur,

verify

that

this

brush

has

not

been

displaced.

e)

Parasitic

Noises

from

the

Motor

These

are

caused

by

commutation

of

the

motor.

Th

s e

are

easily

icJentifiabJe

in

that

they

are

related

to

the

rotation

of

the

motor.

Th

ey

can

be

recJucec!

to

U

,en

".!

extent

at

the

source

by

first

che

cki

ng

that

the

commutator

is

in

guod

cll'zlr1

order

and

that

the

brushes

make

good

contact,

and

then

by

rernoving all

possible

paths

of

transmission

between

the

motor

ancJ

the

amplifiers.

There

are

various

routes:

Magnetic

induction.

The

rotor

carries a current

affected

by

rarasltics

and,

therefore,

generates a magnetic

field

containing

parasitic

com

poncnts.

Various

screens

of

permallo

y C

are

fitted

to

eliminate

this

ancJ

they

should

not

be

disturbed.

It

is

norm

al

that a certain level of

pa

rasitic

noi

SE'S

should

be

observable

when

the

recorder

is

open

because

part

of

the

scrcpning

is

on

the

bottom

of

the

case.

Electrical

coupling

at

low

frequency.

The

motor

current

has a parasitic

component

which

is

by-passed

by

smoothing

condensers.

The

mvthod

of

connections

to

earth

has

been

very

carefully designed and

any

modification

can

provoke

the

occurence

of

parasitic

noise.

Electrical

coupling

at

high

frequency.

The commutator,

as

with

all

contact

brakers,

beha

ves

as a very small

spark-t

ype

emitter.

The

consequent

wa

ve

trains

which

are

generated

are

very

easily

propagat

ed

and

then

rectified

by a semiconductor,

and

there are a

lot

in

thE:'

Nagra.

This

method

of

coupling

is

blo

cked by

ferrite

filters

in

the

c:o

nnt·ct

ing

leads.

Page

16

Motor

spindle.

The

motor

spindle

turns

in a ball

race

indise

the

motor

and

on a bearing

holder

und

erneath

on

the

end

plate.

It

can

happen

that a film

of

lubricating

oil

and,

on

the

bearing

holder,

a l

ayer

of

aluminium

oxide

which

protects

the

bearing

holder

and

the

chassis

from

corrosion,

becomes

sufficiently

insulating

so

that

the

spindle

is

no

longer

effectively

earthed.

In

this

case

the

parasitic

in

the

motor

find

another

route

to

earth.

The

parasitics

so

passing may

in

truth

be

extremely

small

but

it

is

possible

that

this

may

happen.

This

trouble

can

be

diagnosed

when

it

is

found

that

the

noise

disappears,

then

the

spindle

is

earthed

by

touching

the

capstan

with a wire

to

earth.

In

general,

it

is

sufficient

to

eliminate

these

parasitics

by

carefully

earthing

the

end

bearing

holder

and

removing

the

oxide

on

the

seat

of

the

screw

holding

the

bearing

holder,

but

in

a

very

bad

case a little

metallic

brush

on

the

back

of

the

capstan

is

obviously

the

most

certain

method.

r--

L-

INSIDE VIEW

OF

BOX

/

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I'

6'

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Speed

stabilizer

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•

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1-,

t-.t:::j

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b

Speed

Commuta_

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C

Frequency

response

curve

correction

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BOTTOM

VIEW

OF

DECK

PLATE

Oscillator
transformer

Premagnetization

Play

back

Bias

Frequency

Filter

\

Take-up

tensiometer

Take-up

clutch

I

\

\

\

~Motor

Collector

""

Tachyrnetrical

Wheel

11

~I

o

and

erase

oscillator

o

Acceleration

Button

©

o

/

NAGRA

III

MODIFICA

TION

NOTE

BEFORE-AFTER

MONITORING

SWITCH

This

Nagra

is

equiped

with a push

button

which

permits

the

selection

of

the

sound

source

to

the

monitoring

earphones

during

recording.

One

can

select

to

monitor

the

signal

already

recorded,

or

the

signal

before

it

is

recorded.

By

pressing

the

BA

switch

(see

photo

below),

the

signal

before

recording

is

selected.

When

the

button

is

not

pressed,

one

has

at

the

monitoring

sockets,

the

signal

as

described

in

article

No.

13

of

the

description

of

controls.

MODIFICATION

NOTE -MICROPHONE

PREAMPLIFIER

This

Nagra

is

equiped

with a new

type

of

microphone

preamplifier

designated

LN.

This

preamplifier

permits

the

selection

of

input

impedance

between

50

ohms

and

200

ohms.

All

that

is

necessary

to

do

in

order

to

change

from

one

impedance

to

the

other,

is

to

rewire

internally

the

connections

on

the

input

transformer.

For

wiring

information,

please

refer

to

the

mike

preamplifier

section

of

the

Nagra

wiring

diagram

included

in

the

instruction

manual

dated

May

1st,

1963.

KUDELSKI

6,

ch.

de .I'Etang, Paudex - Lausanne, Switzerland

MODULATION

METER

&

I
I

I

~

-

........

I

~

.

L

Jp,;

0

.

..ISl

..II

1

"-:"T~

L ! T -- I (..

MICROPHONE

PRE-AMPLIFIER

LINE

AMPLIFIER

OUTPUT

TRANSFORMER

AUTOMATIC

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Subjective

tests

\1i

th

mike

microphone,

casque

et

haut-parleur

10)

Contrale

de

phase des

and

recording

heads

and

10)

Phase

control

of

reproducE

tE~tes

d'enregistrement

et

-

de

lecture

et

du

transfor-

mateur

de

sortie

output

transformer

11)

Signal

de

re

ference

11)

Reference

signal

-

Start-stop

pour

BH

Start-stop

for

BH

only

2

12)

OUTPUT

AMPLIFIER

12)

AMPLIFICATEUR

DE

SORTIE

Line

input

sensitivity

Sensibilite

d'entree

Accessory

socket

input

sensitivity
Distorsion:

H2

(at

0 db -

1000

cIs)

H3

Signal

to

Noise

ratio

Line

output

level

Modulometer

reading

13)

PLAYBACK

CHAIN

Signal

to

Noise

ratio

Tachometric

signal

rejection

14)

Reproduce

signal

level

at

o db -

l5"/s

*

Monitoring

PLAYBACK

Line

Hi-Fi

PLAYBACK

15)

Recorded

signal

level

at

o db -

l5"/s

Monitoring

RECORD

Distorsion:

16)

Erasure

*

17)

MIKE

PREAMPLIFIER

Signal

to

Noise

ratio

Sensitivity

Frequency

response

Automatic

level

Control

18)

PILOTTONE

SYSTEM

*

Reproduce

signal

level

Recorder

signal

level

Clapstick

signal

Sound-Pilottone

rejection

Pilottone-Sound

rejection

Closed-loop

speed

control

with

SLO

ligne

Sensibilite

d'entree

accessoires
Distorsion

H2

(a

0 db -

1000

Hz)

H3

Rapport

signal/bruit

Niveau

de

sortie

ligne

o

\y:l

V

~,~

mV

0

,

3.

%

o 7 %

- 1 -

~

b

4,4

V

Indicat ion

du

modulomet

re

+~\I db

13)

CHAINE

DE

LECTURE

Rapport

signal/bruit

15"­19 cm-CCIR

7,5"-

NAB

Residu

tachymetrique

14)

Niveau

de

lecture

a

o db -

38

cm/s

*

Monitoring

PLAYBACK

Ligne

Hi-Fi

PLAYBACK

15)

Niveau

d'enregistrement

a 0 db -

38

cm/s

Monitoring

RECORD

Distorsion:

16)

Effacement

*

17)

PREAMPLI

MICRO

db
db

-

]2,

db

10.S::

mV

db

Rapport

signal/bruit

-

1l~

dbm

Sensibilite

0 I IJ

mV

Reponse

en

frequence:

30

H?

-0

1

4-

db

18

kHz

Compresseur

automatique

18)

SYSTEME

NEO-PILOTE *

Niveau

de

lecture

50

~V

Niveau

d'enregistrement

Claquette

Residu

Son-

Pilote

Residu

Pilote-Son

-

Asservissement

de

vitesse

avec

SLO

-0

(.

db

f

v

lor

db

TECHNICAL

COMMENTS

ON

THE

TESTS

4)

Current

consumption

The

supply

voltage

shall

be

18

v.

5) No

speed

overshoot

of

starter

circuit

This

test

shall

be

carried

out

with a supply

voltage

of

24

v.

6)

Speed

control

Average

speed

stability

(or

absolute

speed

) .

N

ote:

This

measurement

can

be

carri

e d

out

with

the

aid

of a standard

test

tape

and a frequency

meter,

or

with

the

aid

of

the

stroboscopes

which

are

found

on

top

of

the

flutter filters.

A

displacement

of

one

point

in

10

seconds,

corresponds

to a speed

error

of

0.1

%.

It

is

well

to

remember

that

one

quarter

of

a

non-tempered

tone,

corresponds

to a frequency

variation

of

3%.

Therefore,

an

error

of

0.3

%

in

absolute

speed,

corresponds

to a pitch

variation

of

1/40

of a tone.

NOTICE:

It

is

imperative

to

use a crystal

con-

trolled

ligh

source

when

checking

the

strobos-

copes.

The

frequency

error

of

the

mains,are

in

general

larger

than

the

speed

error

of

the

NAGRA.

The

reason

for

which

precision

of

this

order

is

important,

is

the

application

of

the

NAGRA

in

telemetry.

In

our

test

laboratory,

the 3 speeds

of

15",

7

,5"

and

3,75"

are

ajusted

by

means o f a

speed

standard

test

tape

on

which a signal

of

1000

cis

!O,l % has

been

recorded,

and

our

WFM

speed

me-

.

/.

COMMENTAIRES

TECHNIQUES

SUR

LES

MESURES

4)

Consommation

de

courant

La

tension

d'alimentation

est

de 18

V.

5)

Pas

d'emballement

au

demarrage

On

procede a cet

essai

avec

une

tension

de

24

V.

6)

Controle

de

vitesse

Stabilite

de

la

vitesse

moyenne

(ou

vitesse

absolue

) . N

ote:

Cette

mesure

peut

se

faire

soit

avec

un

ruban

etalon

et

un f

requencemetre

au

discriminateur,

soit a l'aide

de

stroboscopes

places

sur

les

guides

rotatifs.

Le

deplacement

d'un

point

en

10

secondes

correspond

a un

ecart

de

vitesse

de

0,1

%.

Rappelons

qu'un

quart

de

ton

tempere

correspond

a

une

variation

de

frequence

de

3%.

Une

erreur

de

vitesse

absolue

de

0,3% equivaut

donc

a

1/40

de

ton.

ATTENTION:

Pour

des

mesures

precises,

il

faut

utiliser

une

source

de

lumiere

pulsee,

pilotee

par

quartz;

les

ecarts

de f

requence

du

secteur

etant

souvent

superieurs a ceux

du

NAGRA.

La

recherche

d'une

si

grande

precision

dans

ce

domaine

est

justifiee

par

les

applications

du

NAGRA

en

telemesure.

Dans

notre

laboratoire

de

contr6le,

les 3 vites-

ses

de 38

,1

cm,

19,05

et

9,5

cm/s

sont

reglees

avec

une

bande

de

vitesse-etalon

ayant

une f re-

quence

de

1000

:0,1

%,

ainsi

que

notre

instrument

• / ••

VJ

ter

having a calibrated

discriminator.

Drop

of

speed

due

to

braking

of

the

capstan

This

test

is

carried

out

by

braking

of

the

caps-

tan

until

the

motor

current

consumption

reaches

twice

the

normal

one.

The

purpose

of

this

test

is

to

chek

the

safety

margin

of

the

servo-ampli-

fier.

7)

Wow

and

Flutter

This

test

is

carried

out

in

PLAYBACK

by

means

of

a

standard

test

tape.

The

reading

is

taken

on

our

WFM

instrument,

which

gives

the

peak

value

of

the

weighted

wow

and

flutter

according

to

the

DIN

45507 specifications.

8)

Battery

voltage

limit

Recording

and

playing

back

simultaneously

while

lowering

the

power

supply

voltage.

The

limit

voltage

is

the

supply

vOltage

at

which

the

alarme

signal

appears.

The

recorder

should

function

correctly

down

to

that

voltage.

Test

conditions:

(worst

case)

Speed:

l5"/s

End

of

a 7"

reel

Limit

vOltage

of

Modulometre

It

is

that

supply

vOltage

which

corresponds

to

the

red

mark

on

the

Modulometer.

The

reading

is

made

in

PLAYBACK.

This

voltage

is

lower

than

12,5

V.

Its

value

is

generally

higher

than

the

latter

by

0,5

V.

(worst

case)

de

mesure

WFM

equipe

d'un

discriminateur

eta-

lonne.
Baisse

de

vitesse

par

freinage

du

cabestan

On

procede a cette

mesure

en

freinant

le

cabes-

tan

jusqu'a

ce

que

la

consommation

du

moteur

atteigne

le

double

de

la

valeur

normale.

Ceci

a

pour

but

de

verifier

la

reserve

de

marche

de

l'asservissememt.

7)

Pleurage

et

scintillement

Cette

mesure

est

faite

en

PLAYBACK

au

moyen

d'une

bande-etalon.

La

valeur

est

mesuree

sur

notre

instrument

WFM,

qui

donne

la

valeur

de

pointe

du

pleurage,

apres

passage

dans

un

filtre

de

ponderation

prevu

par

la

norme

DIN

45507.

8)

Tension-limite

des

piles

Enregistrer

et

lire

simultanement

tout

en

bais-

sant

la

tension

d'alimentation.

La

tension

li-

mite

est

la

tension

pour

laquelle

le

signal

d'alarme

apparait.

L'appareil

doit

fonctionner

correctement

jusqu'a

cette

tension.

Conditions

de

mesure:

(cas

le

plus

defavorable)

Vitesse:

38

cm/s

Fin

de

bobine

7"

Tension

limite

du

Modulometre

C'est

la

tension

d'alimentation

correspondant

a

la

marque

rouge

au

Modulometre.

La

lecture

se

fait

en

PLAYBACK.

Cette

tension

doit

etre

infe-

rieure a 12,5

V.

Sa

valeur

est

generalement

de

0,5 V superieure a la

tension

limite

definie

ci-

dessus.

(cas

le

plus

defavorable)

~----------------------------------------------------------------------~----------------------------------------------------------------------~

~

__________________________________________________________

__________________________________________________________

9)

Reproduce

signal

level

The 0 db (=

4,4 V Line

Output)

correspond

to

a

r.m.s.

value

of

the

recorded

flux

of

200

milli-

Maxwells

on

the

tape.

This

test

is

carried

by

means a

level

test

tape.

16)

Erasure
We

guarantee

an

erasure

of

at

least

75

db

for

a

signal

recorded

on a Scotch

tape

type

102

at

the

level

of

200

mMx.
Measurement
An

800

cis

signal

is

recorded

at 0 db,

with

a

tape

speed

of

l5"/s,

and

then

erased

using

the

internal

facilities.

The

ratio

between

the

si-

gnal,

as

recorded

and

the

non-erased

residue

gives

the

efficiency

of

the

erasure.

Signal

to

Noise

ratio

The

measurement

is

performed

with

the

"A"

wei-

ghting

network

in

accordance

to

I.E.C.

standards

for

Precision

Sound

Level

Meters

(Helsinki

1961)

The "A"

weighting

network

of

the

I.E.C.

is

prac-

tically

the

same

as

the

ASA A american

specifi-

cations.

In

our

test

laboratory

the

reading

is

made

on

a

Bruel & Kjaer

Audio

Frequency

Spectrometer

type

2112.

L-

9)

Niveau

de

lecture

Le

niveau

0 db

(=

4,4

V a

la

sortie

ligne)

cor-

respond a la

valeur

efficace

d'un

flux

de 200

milliMaxwells

sur

la

bande.

Cette

mesure

est

operee

au

moyen

d'une

bande

etalon

de

niveau.

16)

Effacement
Nous

garantissons

un

effacement

de

75

db

ou

mieux

d'un

signal

enregistre

102

au

niveau

de

200

mMx.

Procede

de

mesure

On

enregistre

au

niveau

0 db

a

38

cm/s

puis

on

efface

avec

sur

ruban

Scotch

un

signal

de

800

Hz

l'appareil.

Le

rapport

entre

le

signal

non

efface

donne

l'ef-

ficacite

de

l'effacement.

Rapport

Signal/Bruit

La

mesure

est

faite

avec

le

filtre

de

ponderation

"A"

prevu

par

les

normes

internationnales

de

la

C.E.I.

sur

les

mesures

acoustiques(Helsinki

1961)

Le

filtre

"A"

prevu

par

les

normes

C.LI.

est

pratiquement

le

meme

que

Ie

filtre

ASA A des

normes

americaines.

Dans

notre

laboratoire

de

controle

la

mesure

est

realisee

au

moyen de

I'analyseur

Bruel & Kjaer

type

2112.

J-

-J~