Revox A77 Service Manual

Fig. 12.1.-4.
52
51
14
50
12.1.3. Use of the Dolby Circuit in the Tape Recorder
To achieve correct performance both the record and play-
back sections must work at identical levels, that is, the tape
recorder must have unity gain and a very linear frequency
response from the output of the record processor to the
input of the playback processor. All Dolby- encoded tapes
must be recorded with the operation of the noise reduction
circuitry referred to an absolute level of tape flux. Because
the same flux level is also standardized for playback, inter-
changeability of Dolby- encoded tapes is assured. The
standard tape flux is 185 nWb/m which corresponds to
the Ampex Reference Level on Ampex calibration tapes with
NAB equalization.
Any change in gain between the output of the record
processor and the tape would be equivalent to a shift in the
processor's characteristics. Differences in tape sensitivity
must therefore be balanced out, using the RECORD CALI-
BRATION Q / 0 control provided on the front panel for
this adjustment.
Adjustment of R EC CAL Control
1. Load the recorder with tape of the kind to be used.
2. Set record level controls° 0 to zero.
3. Turn selector switch Q to CAL.
4. Set the recorder to RECORD.
5. Adjust R EC CAL controls CD / Q until each meter reads
O VU.
6. Return selector switch Q to INPUT or TAPE.
Be careful not to accidentally select the CAL position during
source- tape switching while recording, or the calibration
oscillator tone will be superimposed upon the signal being
recorded.
Fig. 12.1.-5.
• on/off-tape monitor selector
• Record volume control Ch I
• Record volume control Ch II
• Record pre- selector Ch I
• Record pre- selector Ch II
32
35
15
17
53
DOLBY IN/OUT
Switch to activate or to deactivate the DOLBY noise
reduction circuits.
RECORD CALIBRATION
• Record Calibration for Channel I
• Record Calibration for Channel II
FILTER IN/OUT
Switch for turning the multiplex filter on or off.
Index Numbers
The index numbers 50 to 53 are used for identifying the
additional operating controls on the DOLBY equipped RE-
VOX A77 tape recorder. All other index numbers make
reference to the operating instructions for the standard
version except for the following changes:
Standard Recorder
Button Speakers off
Button Reel Motors off
Monitor selector0:
— Position NAB
— Position IEC
DOLBY Version
omitted
omitted
corresponds to TAPE
replaced by Calibrate
( new function
12.1.3.

Revox A77 Specifications

General

Wow and Flutter	0.08% (7 1⁄2 ips)
Frequency Response	30Hz to 20kHz (7 1⁄2 ips)
Signal to Noise Ratio	60dB
Type	Reel-to-Reel Tape Deck
Track System	4-track, 2-channel stereo/monaural
Reel Size	Up to 10.5 inch reel
Motor	2 x reel, 1 x capstan
Inputs	Mic, Line
Outputs	Line
Tape Speed	3 3⁄4 and 7 1⁄2 ips