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Revox A77 Service Manual

Revox A77
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'11>
0
dB
-Cr
0
dB
—1448 -
—
24
dB .
—
34
d8
500
2k
5 k
10
k
20
20 50
100
200
Mismatch
Response:
2
dB
Gain
Between
Record
and
Play
Processors
Fig.
12.1.-6.
12.1.4.
Matching
and
Mismatching
The
frequency
response
of
a
record/playback
processor
chain
connected
in
series
hould
be
within
a
tolerance
of ±
1
dB .
Typically, deviations
much
smaller
than
this
are
achieved.
Although
mismatching
may
arise
from
a
number
of
causes,
most
commonly
it
is
the
result
of
incorrect
adjustment
of
the
signal
channel
between
the record
and
playback
processors
for
unity
gain,
either
on
a
wide-
band
basis
or
at
high
frequencies.
The
effect of
such
gain
errors (
wideband)
are
shown
in
Figures
12.1.-6.
and
12.1.-7.
Under
dynamic
program
conditions,
response
deviations
of
this
magnitude
are
inaudible.
Other
sources
of
error
are
incorrect
alignment
or
a
build-up
of
component
tolerances.
Individual variations
in
FET's
are
mainly
responsible
for errors
in
the
processor
charac-
teristics.
It
can
be
seen
that
the
region
most
sensitive
to
mismatch
is
that
at
a
level
of
about —
25
VU;
the
error
will
be
less
at
higher
and
lower
levels.
Basic
Printed
Circuit
Board
1.077.854
This
board
carries
both
plug-in
processors
and
all
of
the
required
interconnections.
Also
on
this
board
is
a
Zener
diode
to
derive
the +
7.2
V
from
the
21
V
supply
and
an
RC
combination
to
filter
out
any
hum
in
the +
27
V
supply
for
the
relay
in
the record
processor.
All
interconnections
between
the
switch
board
and
the
printed
circuit
cards
carrying
the
calibration
potentiometers,
the
power
supply,
the
VU
meters
and
the
switches "
Dolby
in/out", "
Filter
in/out"
and "
Calibration"
are
either
soldered
or
plugged
onto
this
board.
18
dB
—
28
d8
38dB
20
50
100
200
503
2k
5k
10
k
20
kHz
Mismatch
Response
2
dB
Loss
Between
Record and
Play
Processors
Fig.
12.1.-7.
Calibration
Potentiometer
Board
1.077.342
Two
potentiometers
are
mounted
on
this
board
for
indivi-
dual
front
panel
adjustment
of
both
record
channels
to
match
them
to tapes
of
different
sensitivity.
Switchboard
1.077.426
This
differs
from
the
corresponding
board
in
the
standard
version
of
the
A77
in
that
it
carries
the
pluggable
inputs
and
outputs
for
the
Dolby
processor.
The
NAB/IEC
switch
has
been
modified
to
carry
the
function
of
switching
the
VU
me-
ters
for
metering
level
from
the
tape
as
well
as
the
signal
from
the
record
amplifier
which
is
normally
metered
during
recording.
Equalization
characteristics
remain
NAB
in
all
three
positions
of
the
monitor
selector (
Tape-
Input-
Cali-
bration).
Power
Transformer
1.077.524
The
transformer
differs
from
the
standard
version
in
that
the
wire
of
the
winding
for
the
regulated
21
V
supply
has
been
changed
from
0.5
mm
diameter
to
0.9
mm.
Both
32
V
windings
for
the
power
amplifiers
have
been
omitted.
Reel
Motors
Off
Switch
This
switch
had
to
be
omitted
and
the
two
record
calibration
potentiometers
are
installed
in
its
place.
VU
Meter
Level
VU
calibration
is
effected
on
the
DOLBY
playback
board.
The
calibration
controls
in
the
A77
record
amplifiers
are
disabled.
u
LI
LI
u
12.1.4.
L'

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Revox A77 Specifications

General IconGeneral
Wow and Flutter0.08% (7 1⁄2 ips)
Frequency Response30Hz to 20kHz (7 1⁄2 ips)
Signal to Noise Ratio60dB
TypeReel-to-Reel Tape Deck
Track System4-track, 2-channel stereo/monaural
Reel SizeUp to 10.5 inch reel
Motor2 x reel, 1 x capstan
InputsMic, Line
OutputsLine
Tape Speed3 3⁄4 and 7 1⁄2 ips

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