Nagra III User manual
M
ay
1st
1963
INSTRUCTIONS
MANUAL
KUDELSKI
6,
ch. de
,1'Etang,
Paudex -Lausanne, Switzerland
Offic
e-
hours
7.
30
-
12
.
00
a.m.
and
1.
30
- 6.
00
p. m.
(salurda
y
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
71/2"
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
eo
pilot
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
Nagr
a
accessories
such
as
external
m
ic
rophon
e
pr
earn
plifi
e
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
a
pplied
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
performanc
e
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
sp
e
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,
examin
e
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
dischargin
g
the
condenser
too
soon
or
whether
the
charge
on
the
condenser
is
t
oo
sm
a
ll,
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
40
0
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
co
nsumption.
Such
a
short
circuit
can
happen
in
the
windings
or
inside
the
commutator
,
but
such
cases
are
less
likely
in
recorders
which
are
in
ser
v
ice.
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
usuall
y
between
6
and
8
ohms
through
o
ut
the
series.
It
increases
regularly
from
the
first
to
the
last
winding
progressi
v
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
vo
lts
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
perfectl
y
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
it
self
.
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-
ad
justment
made
by
the
aid
of
a
special
machine
is
much
more
accurate
than
that
made
by
adjusting
to
minimum
curr
e
nt.
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
imatel
y
white
noise,
that
is
to
say,
composed
of
all
frequencies
in
th
e
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
agitatio
n
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
nearl
y
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
n
ot
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
a
llowed.
On
the
other
hand,
it
should
not
be
possible
to
hear
such
Page
15
residuals
during
recording
or
play-back
wlthout
signal
on tile
other
two
speeds.
The
l
eve
l
in
general
will
be
b
ettel'
thall
-
80
db.
Various
forms
of
break-through
are
po
ssible:
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
op
era
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
to
uch
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
a
ll
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
l
eve
l
of
pa
rasitic
noi
SE'S
should
be
obser
va
ble
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
d
esigne
d
and
any
modification
can
pro
vo
ke
the
occurence
of
parasitic
noise.
Electrical
coupling
at
high
frequency.
The
co
mmutator,
as
with
all
contact
brakers,
beha
ves
as
a
ver
y
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
ar
e a
lot
in
thE:'
Nagra.
This
method
of
coupling
is
blo
cke
d
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
passin
g
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.
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