Revox A77 Service Manual

u
11
Fig. 5.1-32
Before / After Tape switch
( Playback selector
Playback
Mode Switch
The VU- meter board is linked to the switch board by
connectors. It carries the preselector buttons for CH 1
and CH 2; they switch the record- erase signals. 1 Note that
the audio signal has to be switched inversely on the record
amplifier when neither button is depressed ! I
/ vio HB7
" / 131u HB6
,grn HB5
-yel HB4
org HB3
•red HB2
\ brn HB1
I 7111-
I . 7à
Fig. 5.1-33
CH I
5.2. Input Amplifier ( 1.077.700)
Fig. 5.2-34
CH II
The input amplifier card contains the pre- amplifiers for
both channels.
Input sensitivity is matched through a stepped variable
feedback ( d.c. feedback fixed) at the signal source voltages
AUXILIARY ( 35 mV 1, track transfer 1 8 mV ), RADIO
(2,5 mV ), MICROPHONE high ( 2,5 mV ), MICROPHONE
low 1 . 15 mV ).
Input selector
Resistor R 406 / R 426 ( 100K ) is bridged or reduced by
parallel resistors for this purpose. If R 406 / R 426 is
shorted,amplification of the whole stage is A = 460 approx
with 1K in parallel A = 20 approx, and without parallel
resistor A = 1.2 approximately. Parallel resitors R 316 /
R 317 ( CH 1 ) and R 321 / R 322 I CH 2 I are on switch
board 1.077.435. The output stage configuration has the
advantage that the supply voltage can be fully modulated.
Output voltage is nominally 50 mVac, but it can deliver
up to 6 Vac undistorted.
This corresponds to an overmodulation stability of more
than 40 dB. Aside from the overmodulation stability,
sensitivity matching of the input stage through feedback
has the advantage in that input noise is not worsened by
the series- connected voltage divider.
5.3. Record Amplifier ( 1.077.705)
CH I
CH II
Fig. 5.3-35
The record amplifier cards contain an equalization pre-
amplifier 1 Q 501, Q 502 ), a VU- meter amplifier ( 503 ),
and a driver amplifier 1 Q 504, Q 505 ). At the input
of the equalization pre- amplifier is a bus voltage level of
about 25 mV ( at 1 kHz and nominal input signal, record
regulator fully opened I.
19

Revox A77 Specifications

General

Brand	Revox
Model	A77
Category	Tape Deck
Language	English