ÞAudio Magazine, November 1972
ÞHigh Fidelity, November 1972
ÞStereo Review, August 1972
ÞRolling Stone Magazine, October 12, 1972
ÞHiFi Buyer's Guide, Fall 1972
by North American Publishing Co.
Reprinted by permission from the November 1972 AUDIO MAGAZINE
Whatever we said about the original Revox A77 in October, 1968, could well be repeated here, except that this model is better-being Dolby equipped. There are a few minor differences in appearance and a few in the mechanism itself. The upper portion of the unit-behind the tape reels-now has a stainless steel front over the plastic main panel, whereas the original was dark gray plastic. The lower portion of the first model was brushed stainless steel, while the, current model has a dark gray plastic panel. There are two toggle switches below the controls-the one on the left switches the Dolby circuit in or out in both record and play modes, and the one at the right switches in or out a filter to eliminate interference from stereo multiplex circuitry.
The original machine had a pair of push-push switches to cut off power to the spooling motors and to disconnect the input to the power amplifiers (when included). These have been eliminated and in their place are the two Dolby calibration controls. The monitor-selector switch formerly had three positions for INPUT, tape (NAB) and tape (IEC). The IEC position has been replaced by a CAL position which turns on the calibration oscillator for the Dolby circuitry and enables the adjustment of the proper levels for correct Dolby operation.
The solid tape guide post has been replaced by a springloaded guide post to further eliminate flutter due to varying tape tension in the feed reel, and the left tape guide-formerly a solidly fixed non-rolling roller-is now actually a roller. The right tape guide is still fixed.
The space provided in the earlier model for plugging in the two output amplifiers is now occupied by the Dolby processors, so the unit can not be used to drive speakers, and of course, the cut-off switch is not needed. Brake tension has been reduced to permit editing while the machine is in the stopped position.
But enough of this comparison with the older machine most readers will not have access to the October, 1968 issue, so it is desirable to start from scratch in describing - the machine.
Transport operation is controlled by five pushbuttons at the left side of the control panel-FAST REWIND, FAST FORWARD, PLAY, STOP, and RECORD, the latter a red button which must be depressed at the same time as the PLAY button to put the machine into the record mode. Below these are two controls combined with concentric switches. The left knob controls playback level, the right one the balance. The left switch, actuated by a clear plastic disc at the base of the knob, has four positions - STEREO, CH I, CH II, and MONO. The right switch is marked TAPE, INPUT, and CAL
At the right are the two VU meters, flanked by two red push-push switch buttons to select the channel to be recorded, and below the meters are two more knob/switch combinations. The knobs control the recording levels for the two channels while the five-position switches select the source-two impedances for microphones, radio, auxiliary, and a cross-feed position for introducing echo or for sound-on-sound recording. To the far right is a switch operated by a bar knob to control power and speed, with two positions for each speed to compensate for different reel sizes. Above this switch is a power-on pilot light, not actually necessary since the meters are illuminated continuously when power is on, with a red light in the meter scale to indicate the channel(s) recording.
Between the two sets of controls are three phone jacks-one for headphone monitoring with conventional (but high impedance) phones, and the other two for microphones for the two channels. Above the control panel is the tape-path shield-a plastic strip which swings down out of the way for threading. The reel turntables are at the upper part of the front panel, with spring-loaded sleeves which hold the reels in place on the splined spindles. Between the reels is a 4-digit counter, which resets by a pushbutton.
Along the top at the rear are the connectors for inputs and outputs-a 10-terminal DIN socket for the remote control, with its dummy plug, two holes where the speaker jacks were in the original model, a pair of phono receptacles for AUX inputs, another pair for microphone inputs, (duplicating the phone jacks on the front panel), a 5-terminal DIN socket for RADIO input and output for direct connection to many amplifiers and receivers, and another pair of phono receptacles for outputs. These are followed by a receptacle for the power cord.
The unit is constructed on two cast end trusses which provide a remarkable solidity to the chassis. The several modular plug-in boards are secured along the lower part of the rear with all adjustable controls accessible from the bottom through a cover plate in which all the holes are punched for access, but covered by a paper on which the controls are labeled. The playback modules each have two adjustments-one for output level, and one for the bias trap. The record amplifiers each have five adjustable controls-equalizations for the two speeds, level, meter calibration, and bias trap. The oscillator module has four adjustments-bias for the two speeds on channel I, and the same for channel II.
Above the electronics modules is the relay panel on which are located the three relays which control tape motion. The capstan motor is further to the left (viewed from the rear), and the Dolby processing circuit boards are at the left of the motor. Above are the two spooling motors and the brake System, and between them is the power transformer and the regulating panel. One additional relay is located on the module which contains the dummy load that replaces unused heads to maintain a proper load on the oscillator when recording on only one channel. The Dolby processing circuit boards apparently have no servicing adjustments.
Fig. 3 Frequency response curves for the Revox A77 Dolby B. There was no difference in response between Dolby and non-Dolby operation over a wide range of recording levels. Response drops off slightly above 15 kHz when the filter switch is on.
Wow and flutter were measured, both from a standard tape and on a record-and-play basis. Wow - that below 6 Hz - measured less than 0.02%, while flutter - between 6 and 250 Hz was 0.06% at 71/2 ips and 0.08% at 33/4 ips. Signal-to-noise measured 53 dB unweighted, and 62 dB weighted below the 3% distortion point, which was at +8 recording level (for 1000 Hz). We also measured distortion at several other frequencies and found the same figure throughout. These figures were at 71/2 ips, with only slightly differing figures for 33/4.
Using the Heathkit IB-101 frequency counter, we measured the bias oscillator frequency and found it to 122,508 Hz - close enough to the specified 120 kHz. Crosstalk between the two channels in mono was 62 dB, and in the stereo connection, 48 dB.
Input signals required for 0 recording level were noted as follows: AUX, 15 mV; LO Mic (impedance 50 to 600 ohms) 0.15 mV; HI Mic (up to 100 kohms) 2 mV; Radio, 2 mV (33,000 ohms). Outputs were measured at a maximum of 2.5 V from a source impedance of 600 ohms at the output phono jacks, and 1.22 V from the radio receptacle with an impedance of 2500 ohms.
While the Revox A77 Dolby B is not inexpensive, it must be admitted its performance is exceptional, and if one wants quality, one must expect to pay for it. There is no doubt that the machine is well designed and well crafted. And there is no doubt that its performance is close to that of professional machines. In fact, many are in use in applications where the expense of the professional machines could not be met, and their performance has been uniformly excellent. From this description it must be discerned that we like the new Revox. Try it; you, too, will like it. C G. McProud
by Billboard Publications, Inc.
Reprinted by permission from the November 1972 HIGH FIDELITY
Comment: Some readers, accustomed to associating the Dolby circuit with cassette equipment and a price in the $300 range, may be taken aback by this unit. Since they have been told that cassettes are inherently noisier than open reel because of the slow Transport speed, they may think that only the cassette can profit from Dolby noise reduction. Not so. While Dolby processing offers demonstrably more dramatic improvements in the cassette format, Revox has traditionally designed its recorders for those who want the best that tape has to offer and, indeed, for professional as well as home use. In such a context the Dolby B offers an improvement that is both measurable and audible - and therefore significant.
In other respects the new Revox has not changed much since our report on the original A77 (June 1969). Response and distortion figures are very much the same, though IM distortion has improved markedly, while those for wow and flutter and for such things as noise (Dolby aside) and crosstalk are almost identical. The noise measurements for our Mark III test sample actually were slightly poorer than those for the original A77 because of some 60-Hz hum leakage; when the lab filtered out this hum to simulate expected normal performance the figures are better than those for the original. One change documented by the figures is in the motor drive: The present electronically governed system was unaffected by line voltage changes in the lab tests, though its good accuracy figures were more than matched by the excellent ones supplied by our original sample even at the voltage extremes.
Cosmetically the Mark III is different too, with a dark gray control panel lettered in white. The solenoid controls and the meters, flanked by record interlock buttons for each channel, are the same - as are the input selector and recording level controls for each channel, located below the meters, and the multiposition switch for power (on/off), reel size (large/small), and speed (71/2 / 33/4 ips) at the extreme right. Below the input/recording level controls a 19-kHz filter switch has been added to prevent any subcarrier leak from influencing Dolby action in recording from stereo FM. A similar Dolby on/off switch has been added at the left, below the mode/ playback-level control and the function/playback-balance control. The function control dispenses with the original's IEC playback equalization position; it now has one playback equalization (NAB) and the input position, plus one for calibration of Dolby recording levels.
The Dolby calibration controls are below the long, narrow head-cover panel, which swings out of the way behind the control panel to allow access to these controls, to the mechanical pause and cueing feature, and to the heads (for editing or cleaning). A trough in the head shroud can be used as an editing block, though it provides no razor-blade slot for automatic cut-angle alignment. (We prefer the razor-blade method to Revox's scissor method, outlined in the manual, because in our opinion the latter can too easily produce misaligned tape ends and exposed adhesive.)
On the control panel are a stereo headphone output jack and phone jacks for left and right microphones, connected in parallel to phono-type microphone inputs on the recessed jack panel. There are two microphone positions on the input selectors, which adjust these mike inputs for use with either high- or low-impedance models. Also on the back panel are phono jacks for line output and aux input, plus a DIN input/output ("radio") socket and one to accept an optional remote-control unit. On our sample the panel also was marked for speaker connections, though Revox tells us the Dolby model is not supplied with monitor amps (the Dolby circuitry uses the space originally intended for that purpose) and so will not drive speakers directly. It can, however, be bought in either quarter-track or half-track stereo configurations and in either the home model here reviewed or in a rack-mount version.
We were glad to reacquaint ourselves with the special personality of the Revox, with its somewhat complex but extremely comprehensive control panel. Typical of its design - for example, is the mode switch: separate positions for stereo, left channel only to both outputs, right channel only to both outputs, and mono mix of both channels to both outputs. Common alternative designs would require two or even three controls to set up the same functions and might even omit some (particularly the mono-mix mode). In addition, the Revox remains a fine performer even without the Dolby circuitry.
At this writing Ampex has just announced plans to issue the first Dolby-processed open-reel prerecorded tapes. Pending their availability the Dolby circuit is there for those who want to make their own - live, off the air, or from other recordings. For live use particularly the built-in Dolby system is a great convenience by contrast to the obvious alternative: a top-quality deck plus an outboard Dolby unit. In playing back Dolby off-the-air tapes (which we have been collecting via an outboard unit for some time), we worried at first that Dolby levels might not match the preset Revox playback circuitry. All levels turned out to be within about a dB of the Revox however - a negligible discrepancy and one that should give no qualms to inveterate tape swappers who would like to step up to Dolby processing.
And Dolby processing certainly is in order for longer recordings off the air (operas particularly) where the greater per-pass playing time of 33/4 ips makes it a desirable speed. The 15-kHz limit of FM reception plus the subcarrier filter prevent practical program content at frequencies above the response limitations of that speed, and we found the Dolbyized tapes to be indistinguishable from the broadcast. For live recording or where copies are to be made, we also found the added dynamic range of Dolby processing a marked advantage even at 71/2 ips.
by Ziff-Davis Publishing Co.
Reprinted by permission from the August 1972 STEREO REVIEW
When we tested the Revox A77 tape recorder several years ago (January 1969) we found it to be an outstanding machine in every important respect. The Revox A77 is still with us - a few minor bugs have been eliminated, but it is essentially unchanged - and it has earned itself a solid reputation as one of the top home or "semi-professional" tape recorders. Revox has now added Dolby B circuits to the already very quiet A77 and has released it as the A77/Dolby B. The standard machine without the Dolby circuits is still being manufactured.
A careful external examination is required to reveal the presence of the Dolby system. When the hinged cover plate is lowered to expose the tape-loading path, the two pushbuttons to the left of the heads (SPEAKERS OFF and REEL MOTORS OFF) have been replaced by two Dolby recording calibration knobs. The playback power amplifiers of the A77 have been eliminated from this version, probably to make room for the Dolby circuits.
On the standard A77, thc reel motors can be switched off for easy manual cueing and editing. In the Dolby B version, the brake tension has been reduced so that editing can be performed with the recorder in its normal STOP condition. The tape-monitor switch, operated by a clear plastic ring concentric with the playback balance control, has been modified. In thc standard A77, it provides a choice of NAB or the common European IEC (CCIR) playback equalization, plus input-signal monitoring. In the Dolby B unit, only NAB equalization is available, and the third position (CAL) injects a standard Dolby-level calibration tone into the recording circuits. The Dolby calibration controls are then set for 0-VU indications on the two VU meters, a simple operation normally required only when changing to a different tape formulation.
Below the volume and balance controls is a miniature toggle switch that connects the Dolby circuits into the recording and playback amplifiers. The only other visible difference in the new machine is a second miniature toggle switch on the right side of the panel, below the recording input selectors and level controls. this FILTER switch is used when making Dolbyized recordings from stereo FM broadcasts. It sharply attenuates frequencies above 15,000 Hz entering the recorder to prevent the 19,000Hz multiplex signal from having any effect on the Dolbysystem operation.
In all other respects, the Revox A77/Dolby B recorder appears to be identical to the original A77. It is a three-motor, three-head (quarter-track), two-speed machine operating at
Laboratory Measurements. The Revox A77/Dolby B is factory adjusted for 3M 203 tape, which we used for most of our measurements. The record/playback frequency response was impressively wide and smooth, especially at the low-frequency end, where so many recorders seem to be deficient. It was -2 dB from 20 to 24,000 Hz at 71/2, ips, and -4 dB from 22 to 21,000 Hz at 33/4 ips. We also tried other tapes and obtained very similar results with Maxell UD35-7 and Sony SLH-180 tape. By a slight margin, the best overall performance was obtained with 3M 207 tape. Its response at 71/2 ips was slightly flatter than with the 203 tape, +1 and -3 dB from 20 to 21,500 Hz. At 33/4 ips the flatness was also superior, within -1.5 dB from 30 to 15,000 Hz.
The multiplex filter cut off very sharply at 15,000 Hz. Its attenuation was about 20 dB at 20,000 Hz. As we expected from previous experience with Dolby systems, this one had no discernible effect on frequency response at any measurable level.
The playback frequency response, with Ampex quarter-track test tapes, was about --1 dB from 50 to 15,000 Hz at 71/2 ips, and +2, -1 dB from 50 to 7,500 Hz (the tape's upper limit) at 33/4 ips. The distortion of the Revox A77/Dolby B was lower than that of most high-quality home recorders we have tested. At 33/4 ips, it was about 1.3 per cent at 0 VU, increasing to 3 per cent at about +5 VU. At 71/2 ips, distortion at 0 VU was 0.7 per cent, and it reached 3 per cent between +6 and +7 VU. When the 207 tape was used, the 0-VU distortion was only 0.58 per cent, and 3 per cent was not reached until +9.5 VU.
The recording amplifiers of the A77/Dolby B have extremely high gain. Only 14 millivolts is needed at the AUX inputs for 0-VU recording level, and the high-impedance and low-impedance microphone sensitivities are respectively 1 millivolt and 42 microvolts. At maximum gain settings, the system noise increased about 10 dB, but at any realistic setting of the controls it was very low indeed. Measuring noise in a 250- to 20,000-Hz bandwidth to eliminate the effects of low-level a.c. power-line hum, we found it to be about -57 dB through any input at 71/2 ips, and -52.5 dB at 33/4 ips. With the Dolby system operating, the corresponding figures were -61 dB and -60 dB.
On the face of it, these appear to be very good, though not extraordinary, noise levels. However, when you consider that they are referred to a 0-VU recording level, they are extraordinary. For example, if the 207 tape is used and the noise level is referred to the standard 3 per cent distortion level, the signal-to-noise ratio becomes 66 dB at 33/4 ips and 70 dB at 71/2 ips. These measurements place the Revox A77/Dolby B above all other home recorders we have used in respect to signal-to-noise ratio.
The wow was unmeasurable at either speed (less than 0.01 per cent) and flutter was a very low 0.04 per cent at 71/2 ips and 0.05 per cent at 33/4 ips. Operating speeds were exact, and in fast forward or rewind the machine handled 1,800 feet of tape in about 90 seconds.
Comment. With respect to its actual measured performance, the Revox A77/Doiby B excels in every respect. Operationally, it is smooth, bug-free, and unusually quiet (the motors are inaudible more than a few inches from the machine). In flexibility and overall applicability to serious home recording, one could hardly ask for more.
We have two minor criticisms, both of which were voiced in our review of the original A77. The tape loading path is a straight line across the heads, except for a guide pin at the left of the heads. This changes what could have been one of the easiest-loading recorders to one that requires at least some fumbling in the tape-threading process. We also noted the lack of a PAUSE control. Since the Transport buttons are easy to operate with one hand, this is not too serious a fault, but it would be a convenience to be able to stop the tape in the RECORD mode, and to start it with less of the inevitable transient "wow."
In the light of our measurements, one would expect the A77/Dolby B to have absolutely no effect on the sound of the recorded and played-back program. This proved to be the case, even when recording interstation FM hiss at 33/4 ips. We cannot imagine how the sound quality of this machine could be improved in any way. A fair question might be-why do we need the Dolby B system (at an additional cost of $200-plus) on a recorder that is already one of the quietest on the market? If you are recording from discs or FM radio, it is doubtful that any audible benefit will result from the Dolby system, since the noise in the incoming signal will almost certainly exceed that of the non-Dolbyized recorder. On the other hand, in high quality live recording, it could be considered as the frosting on an already high-grade cake. And, of course, when commercially recorded Dolbyized tapes are released, you will be able to remove most of the hiss which at present is a major drawback in high-speed duplicated tapes.
by Straight Arrow Publishers
Reprinted by permission from the October 12, 1972
ROLLING STONE MAGAZINE
The Top "Semi-Pro" Tape Deck
by Davis Publications, Inc.
Reprinted by permission from the Fall 1972 HI-FI STEREO BUYERS' GUIDE
How do you improve upon an already superb tape deck? If you are Revox you simply avoid gimmicks that would only complicate what is probably the easiest-to-operate mechanism - whether professional or amateur - and concentrate on squashing the tape noise through use of a Dolby B noisereduction system. The fact is, the only apparent difference between the old A77 and the Dolby A77 is the Dolby system. Well, it's the Dolby, but with a big difference. You don't get a calibration tape with the Revox because the machine is supplied so precisely adjusted you don't have to match tapes, make any corrections, or do anything other than record as you normally would.
To avoid unnecessary duplication you can look up the specs on the Revox Dolbyized A77 in the test reports; we'll get right down to basic differences. First off, the only apparent difference between a standard A77 and the Dolby A77 is two small switches at the bottom edge of the front panel. One switch is the Dolby selector, the other is the filter for the FM-stereo pilot signal, as Dolby circuits easily get "loused up" if pilotsignal leakage from a receiver rides along with the audio signal into the recorder. The only other apparent difference is the tape-monitor switch. The original A77 switch had three positions: one for NAB equalized-playback, one for CCIR equalized playback and one for source monitoring. The new tape-monitor switch still has three positions but the CCIR play equalization is now replaced by a Dolby calibration oscillator. By placing the switch in the CAL position, a tone signal is automatically applied to the recording amplifiers.
That's the whole change in external appearance. The other obvious change lies behind the dropdown strip that conceals the tape-drive path and the REEL MOTORS OFF switch on the standard A77. The Dolby A77 no longer has the reel-motor control switch. (Brake tension has been reduced to simplify threading.) in place of the switch are two controls for Dolby recording channels. In typical use you would simply set the tape-monitor switch to CAL and adjust the Dolby-level controls for a zero-VU reading on the meters. That's the whole Dolby alignment procedure.
Where did they put it? Since the Dolbyized Revox A77 has both record and play Dolby equalizers, so you can simultaneously playback the deprocessed recording, a lot of space was required under the deck. The standard A77 already had space for pre-wired sockets that accommodated plug-in power amplifiers. The sockets were also pre-wired to two speaker-output jacks on the connection strip along the top edge of the rear apron. You will find that on the Dolby model the holes for the jacks are now plugged, as the Dolby printed-circuit boards utilize the space reserved for t-he power amplifier plug-ins. This Arrangement retains all the conveniences of the standard A77 such as plug-in record and play amplifiers and complete user access to the bias and equalizer adjustments.
Performance is like WOW! The non-Dolby performance is just as it was for the standard model. superb. (Again, to save space we'll let you refer to the test report in this issue.) The only thing the Dolby does is to reduce the noise level to a rock-bottom -62 dB narrow band, which is superior to the signal-to-noise ratio of many non-Dolby full-track professional recorders. in order to obtain this excellent signal-to-noise ratio you must keep in mind that the A77 is a professional machine and has professional VU-meter calibration: zero VU is 10 dB below tape saturation (3% THD) and you need not reduce the recording level to avoid peak-signal distortion. On the A77 you ride signal peaks right up to "zero VU", and an occasional peak can go above zero VU.
Summing up. Even if the $999 price tag of the Dolby A77 is too rich for your budget, we suggest you listen to one at your local hi-fi showroom just to enjoy truly magnificent sound quality.
REVOX CORPORATION -155 Michael Drive, Syosset, New York 11791 (516) 364-1900
Form # RVI39A
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