Revox A 700 Review
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Extracted text from Revox A 700 Review (Ocr-read)
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. file:///P|/9105%20werkdirectorie/Manufacturers,%20Manuals/Tapedeck/tests\ /9160CMREV-REV-A700.htm (2 of 9)1-11-2003 11:03:47
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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). file:///P|/9105%20werkdirectorie/Manufacturers,%20Manuals/Tapedeck/tests\ /9160CMREV-REV-A700.htm (3 of 9)1-11-2003 11:03:47