The Naked ReVox
from the original article by Alan Holmes

Sooner or later, if music is an important part of your life, you will consider buying a ReVox, simply because it is the Rolls Royce of semi-professional recorders. Manufactured by Willie Studer, famous for Studer Master Recorders, and made to the same high standards, it has no equal. Its capstan motor, for example, is made on the same 8-ton press and is nearly identical to that of the £25,000 Studer A80 24 track machine, to be found in most of the world’s top studios. It also has the same adjustments for bias and equalisation as a professional machine, which means that it can be serviced every year and re-calibrated like new, regardless of age. A thirty-year-old Mk 2 can be adjusted to give the same performance as the much newer Mk 4 providing the heads are not too worn and, for less than £100. You can, if you wish have the knobs and front covers updated so it looks brand new too. Very interesting if you would like a ReVox but find the current new prices of around £3,000 for a standard speed machine beyond your means.

Renowned for its long life under punishing conditions, it is almost impossible to wear out the main bearings. A machine was recently returned to the main agents for service after six years of continuous day and night use in industry, without breakdown. On examination, the heads were very worn indeed but the bearings were perfect. It was returned, after service, ready for another six years punishment.

The wear on the heads is caused by the abrasive effect of the iron oxide particles which coat the recording tape, after all it is only rust in a sophisticated form. The wear pattern takes the form of a flat across the width of the curved head surface and, by measuring this it is possible to tell if the heads need replacing, normally 4mm maximum but sometimes 5mm before the performance is affected. The rate of wear can be reduced by the choice of recording tape, as some brands are more abrasive than others, Maxell and TDK being very smooth closely followed by Scotch 207 recommended by the factory, (their own “ReVox” brand is selected 207) and Agfa PEM.

The life of the heads on early machines was a very conservative 900 hours but the newer heads, which can be fitted to any model for around £500, are again conservatively rated at 5,000 hours. You might consider buying (or already own) a four-track ReVox with worn heads, in which case, for around £650 which includes three new heads and an oscillator coil, it can be converted to the more useful two-track. This has a better signal-to-noise ratio for multi-tracking and is essential for tape edits. Equalisation can be either IEC or NAB.

The factory built high speed machine was more expensive than the standard deck and a conversion of a standard model to high speed costs about £800 but this includes a new capstan motor. All factory built high-speed models have the 7½ ips – 15 ips speeds silk screened on the lower designation plate with the rest of the control functions.

Beware of machines with a stickers over the speed markings or labels which may say, “British High Speed” or “Professional” or similar, sometimes in German. These are cheap conversions, costing around £90, in which only the capstan shaft is changed, or a sleeve may be fitted over the existing one. This doubling of the diameter of the shaft is the correct way to double the tape speed but if the motor is not offset 2.25mm in its mounting as in the factory built machines, the path of the tape and the wrap angle is wrong.  If you increase the diameter of the shaft, this moves the tape away from the head, altering the angle at which the tape passes the minute gap at the centre line of the head. It is important that the tape contact or “wrap” against the head is equal on each side of the gap, being a total of around 5mm. If the angle is decreased the tape will touch more on the left hand side of the head altering the frequency response to the extent of an 8kHz drop at the top end from the 20kHz peak to around 12kHz, which is serious for this class of equipment. The tape will also not stay in the tape guide which keeps it tracking straight over the head resulting in “drop out” or sudden loss of signal when the tape veers off course.

The firms who do these cheap conversions try to compensate for the loss of correct angle by bodging the head mounting plate by filing the holes to push the head down and sideways. The tape guide has to be flattened out and bent to an entirely different shape. Having lost the correct tape path, it is

almost impossible to regain and many of the firms that have done this bodge do not even have the correct equipment to check the performance after it. To tell the correct conversion, look at the end of the capstan shaft and the mounting, these should not be concentric but have 2.25mm or nearly 3/32″ offset in the direction of the digital counter.

The vari-speed conversion is mainly for the ReVox A77’s to be found in most professional recording studios, being used as an echo unit. The motor speed is controlled by a “servo motor circuit board” which governs the speed very accurately by reading the actual rotational speed and compensating the current to the motor by tiny amounts to keep it constant. By modifying this circuit so that the current can be altered manually, a wide range of speeds can be obtained, from around 30 inches per second to nearly zero, and thus a wide range of echo delay times are available. Because of the demand by studios for this type of conversion, the later Mk 4 boards were modified with integrated circuits to make this simpler.

This delay, caused by the time it takes the tape to travel from the record head to the replay head can be eliminated by the “sync” conversion. This modifies the internal wiring to enable the record head to playback on one track whilst recording on the other and is how master recorders operate. It is possible, when multi-tracking, to just switch the output wires so that you hear the existing track in “sync” with the fresh overdub. It rather depends on weather you have the

patience to change the wires for every new track. If you don’t mind the fiddling about then don’t bother with the conversion, but if you’re impatient, then go for a “sync” conversion.

The Dolby-equipped machines are only supplied new and cannot be done by a conversion. They are externally distinguished by a small sliding switch between, and just below, each pair of knobs. Beneath the flip-down lid there are two calibration knobs for setting the Dolby to the tape’s sensitivity.

A cosmetic update to the appearance of a Mk 4 can be done on any previous Mk of ReVox by changing the various parts visible from the front. The drive cover was changed to the later type of dark grey plastic at Mk 3 stage so this is only necessary for Mk 1 and 2 machines. This can be fitted by taking out the two screws at the lower corners and gently pulling so that the clip fasteners at the top come free, the replacement gently pushed on to the three sockets and the screws replaced. The lower front panel is removed in much the same way and in the case of Mk 1s, will need replacing but Mk 2s can get away with it. However the new type of VU meters are fitted. In this case the lower panel will need to be filed slightly larger and the rib between the two metters cut away by the technician fitting them.

The old shell (designation plate) is removed by carefully peeling it from the cover starting from the back where the knob holes allow access to push the shell up with a screw- driver. The new shell is fitted by gluing it to the front, making sure that the Evo-stick or similar does not squeeze out round the edges, so little is needed.

Fitting the new lid, the long flip-down tape path cover, is done while the front is off by loosening the screws of the mounting pivots and un-hooking the springs. To remove the push buttons from the perspex arms on which they are a snap fit, lever a 10p coin between the shoulder on the arm and the button and simply press the new ones in place, making sure that the lip is at the bottom. Very carefully rock the record buttons next to the meters backwards and forwards and they will pull off. All the knobs will pull off too and the skirts should be rocked to avoid pulling the entire tube out. It is not really necessary to change the black VU meters of the Mk 1 and 2 as they are mechanically and electronically the same as the later type and some people prefer them in appearance anyway. So, for around £250, you can make your shabby “old faithful” sparkle like new with the list of parts shown.

To keep the performance like new the heads need demagnetising every few months or so, or more frequently in heavy use. A demagnetiser would cost around £15, and any oxide should be removed before every recording with a tape head cleaning kit. Every year, the machine should go for a service and readjustment, or two years if it only gets occasional use. To keep it performing up to specification. There would appear to be very little that is likely to go wrong so there is no such thing as a clapped-out machine, as it is always going to be cheaper to have it brought up to scratch than to buy a new one, even more so with inflation.

The first ReVox A77 was introduced around 1966 and has undergone a continuous process of development ever since. The chart at the end of this article shows some of the more important changes and the serial numbers when they occurred with approximate year dates, it would though take a few months for the supply pipe line to empty and for the new models to reach the shops.

Modification to the one hole head mounting occurs quite early on in the Mk 1 development, and it is not advisable to consider buying an earlier machine. The second modification shortly after was to modify the brake mechanism to make it less fierce and to prevent it from stretching the tape when braking 101/2″ reels. The third, and most important, was the tape feeler arm mechanism which visually distinguishes the Mk 2 from the Mk 1 and can be found just under the left hand reel next to the head cover. It is a pin (about 3/16″ diameter) protruding about 1″ from the cover and moving in an elongated slot on an arc next to the ball race guide. The back of the tape passes over the pin and its function is to stop the tape snapping taut over the heads and bouncing off when the start button is pressed. Before this modification, a blip of unerased sound was left at the start of each new recording. So the feeler conversion kit at £130.19 (plus fitting) is a worthwhile investment for Mk 1 owners who wish to update to Mk 2.

A change in the front panel moulding, both in material and detail was also made at the Mk 2 stage.  The previous front had a different expansion rate to the shell which covered it and it could as a result bowed out. Visually it can be distinguished by a strip between the VU meters on the Mk 2. When doing a cosmetic update and converting the appearance to Mk 4, it is necessary to also change the front panel of the Mk 1 before attempting to fit the shell which is only about 1mm thick and carries all the labels for control functions.

There then followed six different capstan motors during the run of the Mk 2 so it would be advisable to look for a Mk 2 having the final type motor. By the time the Mk 3 evolved around 1970, the development was almost finalised and the Mk 3 is distinguished visually, apart from the grey lower shell, by the change to white VU meters with a small red window in the centre to indicate the “record” mode. Additionally, an extra bulb was fitted to illuminate the VU meters when the power is on. This modification can be fitted for around £250 to earlier models and involves re-calibration.

The Mk 4 was introduced around 1975 and is built entirely in Germany with the exception of the capstan motor, which is made at a Studer plant in Switzerland. The most important improvement was the Mk 4 heads which have a life five times that of the earlier design and which can be fitted for around £500 to any machine. From a visual aspect, the Mk 4 has a dark grey lower shell and some new (and much better) knobs with solid skirts replacing the earlier perspex see-through type which tended to go yellow with age and be a bit wobbly. All the new buttons and the edges of the knobs and skirts having serrated aluminium edges. The new head cover of dark grey plastic replaced the previous brushed aluminium type fitted to some Iater Mk 3’s.

Buying a second hand ReVox is a fairly safe bet, provided the price is right. But it’s worth bearing in mind that it will probably be with you for a very long time, so the newer and cleaner, the better.

After checking the serial number, found under the hinged flap that covers the voltage selector at the back, examine the heads to find the approximate age and true Mk. Brian Reeves can give you a pretty good idea of the age of a machine from the serial number. Remove the reels, lay the machine on its back and in a good light and pull off the head cover. If there is a lot of oxide caked round the heads, it’s pretty obvious the machine has not been looked after. You could ask if it has been regularly serviced. Next, measure the flat wear mark on the heads and make sure it is less than the 4mm which could mean replacement may be imminent. If it is close, it’s an excuse to knock the price down a bit, as the new heads will cost around £500, although if the price is right this can be an advantage. After all, you start off by having the machine serviced and fitted with new heads, it will then be performing like new. If the machine is said to be fitted with output amplifiers, and you will pay a bit more for this, check by plugging speakers into them. Or, if this is not possible, put the machine in a vertical position, remove the reels and, after taking out the four Phillips screws from the back and removing the remote multi-plug, gently walk the chassis out of the case. You will find the amplifier cards plugged horizontally to the bulkhead next to the transformer on the left. The fact that there is a button on the front of the machine marked “speakers off” means nothing as all decks are supplied ready-wired for the amplifier cards to be just slotted in. They are 8 watts per channel output and can be obtained from Brian Reeves, should you wish, for £128.08 each. Check for genuine high speed if this applies. Having kicked the tyres, so to speak, now for the road test, or a check on all the functions.

To test the playback, it is much easier if there is a good hi-fi to connect up to with preferably a CD or a Stereo Tuner as a source for record. If not, you will need a mike with a jack plug and a pair of low impedance headphones for source and replay.

There are two things to check, the mechanics, which includes the three motors, brakes, pinch wheel, controlled by five push buttons, relays, solenoids, and the electronics which is the record, replay, monitor, and channel selection functions. By testing the electronics, the mechanics will also be checked. Thread the machine with decent recording tape and select 71/2 ips and the appropriate reel size on the power switch. The red power-on light should come on together with the end of tape detection bulb which you can see with the lid flipped down. Press the “play” button, let the tape wind a few turns, press “stop” and reset the counter by the button beside it. From the left of the machine, set the output to 10, the skirt to “stereo”, the next knob to “centre balance”, the skirt to “input”. Set the channel 1 volume to maximum (10) and the skirt to “mic lo”, ditto for channel 2. Next to the VU meters are the press on/press off recording channel selections; press them both off. Press the start and record switches simultaneously and the machine should start. Press on channel 1, leave for ten digits on the counter, press off channel 1 and on channel 2 for ten digits, then press 1 again so both meters are lit for ten digits. Rewind, and connect the output which should have been unplugged, or the headphones. Play back quite loudly through the hi-fi while selecting the appropriate channels on the left-hand skirt, 1 for the digits, 2 for ten, stereo for ten. You should hear a smooth, rustling hiss without any crackles or pops apart from the noise of the selectors.

Reset the input volumes to try a recording from the Tuner or Compact Disc and switch it from “input” to NAB on the monitor selector, this allows you to compare before to after recording. There should be no audible difference between them after setting the output volume to match the levels. Rewind and play back the piece while switching from 2 on the monitor to the source on the hi-fi amp. Again, no audible difference should be heard.

You may notice, when recording in stereo with both channels selected, that the volume controls cross over, volume 1 controls meter 2 and vice versa; this is correct. If all this has been satisfactory then the record and replay circuits are working properly. You can check the sound-on-sound track transfer by selecting record channel 1 channel two off, plug a mic into input one and with the level on the meter set, sing or talk and record on the first track, change the skirt from “mic” to “1 to 2”. Release “record 1”, press “record 2”, and the volume of channel one will now act as the transfer volume when the mike is put in “input two” which will control the mike. The channel one volume will go from the 3 or 4 for the mike to 7 or 8 for the transfer. Turn the monitor to channel two and record a new voice. Playback, and the two voices should now both be on channel two.

The wow and flutter can be checked by recording a piano or plugging a guitar in on “mic lo” and recording long notes and check for any wobble effect. There should not be any audible tremor.

Apart from the click of the solenoids when the buttons are operated and a slight whirring when gathering speed in fast foreword or rewind, the operation of the mechanics should be smooth and silent.

So, having checked the electronics in record and replay, listen carefully for any mechanical noise. Measure the heads and check the serial number and there is no more to do but form an opinion and act accordingly.

If the machine has been looked after then it is very unlikely that, apart from head replacement, any faults should cost more than £80 to cure.

As the new owner of a ReVox, don’t forget to budget for tape at around £40 for a 101/2 ” spool plus you will need a couple of NAB adaptors if you want to use professional tape. Then there is a splicing block for joining the tape when it’s cut, plus leader tape and small empty spools if you are making demos, not forgetting splicing tape to stick it all together. A couple of rolls of tape and all the other stuff can easily come to £100 or more, not to mention a demagnetiser if you don’t have one. You will also require a spare 101/2″ empty spool which will set you back around £15.

Many thanks to the service and sales departments of F.W.O. Bauch Ltd., who were the main Revox and Studer agents in England.

Any queries, request for spares, conversions or service should now be addressed to:

Brian Reeves
184 Finney Lane
Cheadle
Cheshire
SK8 3PU
Tel. 0161 499 2349
Fax. 0161 499 9381

Appointed by ReVox GmbH as their authorised service centre for the UK.