Page 1
1975 Revox A700
operates in the trailing position by a solenoid-operated arm, which also\
manipulates the hinged replay head
hum screen.
All the tape transport drive functions are electrically interlocked, and\
tape tension is even controlled in the
start and stop modes with a resulting smooth operation without any tende\
ncy to throw loops or other
untoward habits. It is quite possible to go directly from fast wind to r\
ecord without disaster-the tape stops
from fast wind, is lowered on to the heads and proceeds in the record mo\
de!
However, not all is perfect; one shortcoming is that, in spite of the fa\
ct that tape motion is detected and the
tape end is optically detected, when the tape comes to a finish the reco\
rder takes a considerable time to stop
the take-up spool with the result that tape can fly all over the place. \
This defect is caused by too much inertia
and too little friction around the tape motion-sensing roller. A further\
matter is that, in my opinion, the fast
wind modes are too fast, such that even 3M type 207 with its matt back does not give a very clean wind on
the take-up spool.
All function controls are illuminated push buttons, the current function\
(s) showing a white light in the case of
non-record functions and a red light in the case of record functions. Th\
e three tape speed selection buttons
are only illuminated when the selected tape speed has been attained, pro\
viding a safety factor when
changing speed. Other than the normal tape movement buttons, there is a \
non-locking 'pause' button which
operates in any mode, including fast wind and two further control modes.\
One of these does a fast rewind
when pressed and reverts to play when released-very useful for editin\
g; the other button provides an 'auto
function whereby the recorder optically senses a spliced 'window' at the\
ends of the tape. When the end is
reached, it rewinds and reverts to its original play or record mode at t\
he beginning of the tape.
Access to the heads for editing is quite good, and certainly there is no\
problem in gaining proper access for
cleaning and de-gaussing. However, it is not possible to listen in the f\
ast wind modes where the tape is
removed from the heads by two solenoid-operated guides. Rock and roll op\
eration is possible in the stop
mode.
Electronics
All the electronic components are mounted on printed boards, most of whi\
ch are identified with component
references as an ease to servicing. The general arrangement is that smal\
l boards plug into a mother board,
which contains a number of components; however, access to these and othe\
r components is excellent and
the many integrated circuits plug into sockets as a further aid to servi\
cing. The overall standard of
construction is excellent and the power supplies, which can be operated \
from all the common mains voltages
and frequencies, are protected by some eight identified fuses. One small\
irritation is that the mains lead is
not of the plug-in type; however, plenty of storage space is provided fo\
r it and its plug.
On the record side comprehensive mixing facilities are provided, selecti\
on of stereo inputs being by means
of two input selector switches, each of which has two (left and right)\
slider-type level controls. One selector
has positions for microphones of high or low sensitivity, RIAA phono, ra\
dio or auxiliary inputs, while the
second selector provides for further microphones of high or low sensitiv\
ity, multiplay/ echo, an auxiliary input
and an off position.
The microphone inputs are balanced 6.35 mm jack sockets on the front pan\
el and, with the exception of the
radio input, which is a five-pole DIN socket; the remaining rear panel i\
nputs are phono sockets. A further
slider control is provided for setting master level, recording on either\
or both of the half tracks which are
selected by illuminated pushbuttons.
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Page 2
1975 Revox A700
Two VU meters are provided for monitoring level in the before or after t\
ape conditions and are also fitted with
peak indicator lights which have a relatively fast response. I am, howev\
er, surprised that Revox have not
gone to peak type meters.
The entire replay section is switched to before or after tape by the sam\
e switch as the level meters, and can
also be switched to the four modes of operation-stereo, left, right o\
r mono. However, of the two available
line outputs, one is before the mode switch and the other after. These l\
ine output phono sockets and the DIN
type record/play socket are at fixed level and occur before the tone con\
trol circuits which affect the remaining
outputs.
These remaining outputs comprise a power amplifier output in the form of\
a DIN socket and two headphone
outputs in the form of stereo jack sockets on the front panel; one of th\
ese disenables the power amplifier
output when the phones are inserted. These outputs are controlled by a s\
lider gain control and are affected
by the bass and treble controls which take the form of rotary switches. \
In addition to the audio facilities, the power amplifier output supplies\
a 20V dc line for switching the mains in
the auxiliary power amplifiers made by Revox. As this socket is a standa\
rd 180° DIN socket it follows that
some caution is required not to attach other equipment to the 20V dc lin\
e. Further sockets are provided for
remote control, and for external speed control; a dummy socket being fit\
ted to the review machine for the
future addition of slide synchronisation.
Perhaps unfortunately, there is no provision for the addition of noise r\
eduction systems, but such an addition
should not be difficult as a customer modification.
Replay performance
Checking of the replay equalisation to the NAB standard was accomplished\
by means of DIN calibration
tapes manufactured by BASF which are, themselves, subject to a tolerance\
of
1 dB at high frequencies. It
is therefore most encouraging to report that the Revox performance was w\
ithin
0.8 dB from 40 Hz to 18
kHz at a tape speed of 38 cm/s and
1.2dB from 40 Hz to 18 kHz at 19 cm/s or from 40 Hz to 16 kHz at 9.5
cm/s. Clearly the machine had been most carefully aligned, and this was \
confirmed by checking azimuth in
terms of relative phase between tracks.
The signal-to-noise performance in terms of reference level to noise is \
also excellent as is to be seen from
the following figures which show the performance of the replay amplifier\
system without tape but with all
motors running (see table 1).
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