Revox A 77 Dolby B Owners Manual

Page 1

Operating Instructions
for the REVOX A77
equipped with

DOLBY B System

Compared with the standard version, the
A77 tape recorder with DOLBY B elec-
tronics features a few additional operating
controls. The following instructions are
with reference to theadditional operations
required when utilizing the DOLBY noise
reduction system:

Before switching your recorder on, please
read carefully the instructions ( brief
operating instructions) for the standard
model, while also paying attention to the
designations used for the operating con-
trols as shown in the illustrations on the
following pages 2/3.

DOLBY is a registered trade mark

lnstruktionen fiir die
Spezialausffihrung
REVOX A77 mit
DOLBY- 3- System

Die DOLBY-Ausfiihrung des Tonbandge-
rates A77 verfiigt gegeniiber der Standard-
Ausfiihrung iiber einige Bedienungsele-
mente mehr. Die nachfolgenden lnstruk-
tionen beziehen sich nur auf die zusiitz-
lichen Bedienungsvorgénge bei Betrieb
mit eingeschalteter DOLBY-Elektronik.

Bitte studieren Sie vor dem ersten Ein-
schalten des Gerétes die Anleitung (Kurz-
anleitung) der Standard-Ausfiihrung und
beachten Sie gleichzeitig die Bezeich-
nungen der Bedienungselemente auf den
Abbildungen der Seiten 4/5.

DO LBY ist ein geschiitztes Warenzeichen

Mode demploi

du modéle spécial
REVOX A77

avec systéme DOLBY B

La version DOLBY du magnétophone
REVOX A77 comporte plusieurs ele-
ments de commande complémentaires,
par rapport au modéle standard. Les in-
structions suivantes se rapportent aux
opérations supplémentaires a réaliser Iors-
que le systéme DOLBY est en fonction.

Avant de mettre le magnétophone sous
tension, il faut prendre connaissance du
mode demploi du modele standard at
tenir compte, en méme temps, de la dési-
gnation des éléments de commande
apparaissant aux pages suivantes 6 et 7.

DOLBY est une marque déposée

DCI

REVOX

DOLBY SYSTEM

Page 2

Operating Instructions
for the REVOX A77
equipped with

DOLBY B Noise
Reduction System

Index Numbers

The index numbers 50 to 53 are used for identifying the additional operating con-
trols on the DOLBY equipped REVOX A77 tape recorder. All other index numbers
make reference to the operating instructions for the standard version except for the
following changes:

Standard Recorder DOLBY Version
SPEAKERS OFF 41 omitted

REEL MOTORS OFF 42 omitted

Monitor selector 14:

- Position NAB corresponds to TAPE
- Position IEC replaced by Calibrate

(new function)

1. Operation without DOLBY- Electronics

When it is desired to record or to playback without the DOLBY Noise Reduction
System, place the DOLBY switch 50 into position OUT. The recorder will then
function like any standard REVOX A77 tape recorder.

2. Recording DOLBY Encoded tapes

It is important that the following conditions are being met in order to obtain the full
benefit of the DOLBY B noise reduction process.

Signal to Noise Ratio of the Sound Source

The DOLBY system reduces only those noise components which originate between
the record and playback process; in other words, it affects tape hiss only. Noise
which is already present at the input to the recorder cannot be eliminated. It is
therefore, necessary that the original sound event provides an exceptionally wide
dynamic range (signal to noise ratio of at least 65 to 70 dB).

Equal Level Requirement for Record and Playback

The DOLBY noise reduction system operates with a dynamic filter whose charac-
teristics are determined by the constantly varying sound levels. To ensure a play-
back performance which is an exact mirror image of the record process, it is
absolutely essential that the record and playback levels are equal. This is achieved
by a special gain calibrating circuit (record calibration) which enables the operator
to compensate for differences in sensitivity between different tape oxides (or even
between batch differences of the same oxide).

3. Record Calibration (prior to recording)
The following calibration procedure is to be performed prior to each recording.

1. Switch the recorder on by selecting tape speed and reel size. Load recorder with
tape.

.Put DOLBY electronics into circuit by flicking switch 50 into position IN.
. Close record level controls 15 and 17 by turning them fully anticlockwise.
. Press channel selector buttons 32 and/or 35.

. Turn monitor selector 14 to position CAL.

. Start machine in the record mode.

. The VU meters 33 and 34 will deflect to an undefined reading. Now adjust the
CALIBRATION CONTROLS 51 and 52 until a reading of exactly 0 VU (100%)
is obtained on the channel which is to be used.

Control 51 Adjustment for Channel I VU meter 33
Control 52 Adjustment for Channel (I VU meter 34

8. With the calibration procedure completed, turn monitor selector 14 to position
TAPE (off tape monitoring).

Nam-BOON

ll