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Revox A77

3 Motor 2 Speed Reel to Reel Tape Recorder

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Revox A77


The well known reliability of the Revox A77 is a result of a professional design concept, a concept which successfully combines the advantages of a solidly built tape transport mechanism with those of an advanced electronic circuit design.

A 3 motor transport mechanism with electronically regulated capstan motor and solenoid operated servo brakes possesses few parts which are subject to mechanical wear.

The use of a die-cast motor chassis and head support ensures that a high degree of mechanical precision and long term stability are maintained, even under excessively heavy use.

The mechanical and electrical properties thus complement each other in a most successful way.

Models include the A77 professional, A77 SLS (super low speed) for up to 12 hours of recording, and the A77 Autostart (Vox) for security applications.


Motor: 2 x reel, 1 x capstan

Reel size: up to 10.5 inch reel

Equalization: NAB, IEC

Tape speeds: 3 34  7 12 ips

Wow and flutter: 0.08% (7 12 ips)

Frequency response: 30Hz to 20kHz (7 12 ips)

Signal to Noise Ratio: 62dB

Total harmonic distortion: 0.6%

Crosstalk: 45dB

Input: 35mV (line), 0.15mV (mic)

Output: 1.2V (line)

Output power: 8 watts

Semiconductors: 54 x transistors, 32 x diodes,

Dimensions: 415 x 359 x 180mm

Weight: 33lbs



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Reviewed Dec 06th, 2019 by

I had fixed a number of these machines back in the 1970s when I was an electronic repairman. The previous technician had butchered a lot of these decks and since I was able to order new parts easily , I got many of them to work. I have aligned and adjusted them (levels, bias, equalization, head alignment) and replaced caps that have gone bad. I still own one of these, made many recordings on it, played some tapes recently on it-and it has such a fine, clear sound. make sure the heads are cleaned to avoid a mushy sound.

Reviewed Jan 23rd, 2019 by

Very nice tape recorder to have unfortunatly lost many years ago...Have since bought another A77 MKIII and have servo board problems I am looking for a circuit diagram of this board however the manual in HiFi engine here does not have the I presume a later board info The board I have has a Trim Pot and Variable resistor trimmer There are no IC Chips on the board just transistors about 8 of them and one metal power transistor on a heatsink .
Any help would be appreciated.. Thanks Paul S

Reviewed Jul 02nd, 2018 by

very good

Reviewed Mar 07th, 2018 by

What a fantastic resource! Thanks so much for letting me find you.. ;-
How do I tell what version my A77 is? I bought it new in either 1970 or 71 (for £170 - three months wages then!), but it hasn't been in use at all since about 1990. Having fired it up recently, the capstan motor runs very slowly, so I'm guessing there's a dried-up electrolytic cap on the motor control board or some such. Any clues before I set about it?

Reviewed Feb 17th, 2018 by

I own a A77, B77, Crown 700 and a Teac X1000R, all excellent open reel tape recorders. The A77 is, in my view, the most elegant design. This 10 reel deck is physically compact and the teak cabinet is classic. The deck has excellent sound, if recapped and recalibrated. The transport lacks advanced logic so one does need to exercise a bit of patience with the controls or risk spilling tape. Mine includes Dolby noise reduction which has come in handy a few times as some tapes that I have transferred to digital for friends were Dolby encoded.

Reviewed Mar 27th, 2016 by

Good solid Reel Deck. Great recording and playback. I have this deck for almost 10 yrs, never failed me.

Reviewed Apr 09th, 2015 by




re: A77

I'm working on an A77 S/N G109211, that has lost the 'end of tape' function. It just keeps going...and going... and going ;-). I think it's either the photocell or the amplifier that follows it. Problem is, the manual posted here seems to be a different control board with all different components on it. One of the two transistors, a BC317Bm doesn't appear to be the original but who knows. It reads very high leakage E-C and B-C, normally it would probably be OK.

Two questions I guess.... does the photocell in these generally cause issues, and (2) is there any possibility of finding the proper version of the schematic?


re:Revox A77

Hi, picked up my cousins A77 and cleaned it pretty well but can’t get it into PLAY. I have the owners manual and am threading it properly. FF/REW are fine. Where should I start?

re: A77

I have one for sale, but don't quite know where to put it and what I can ask for it.

re: A77

Biasing this thing is tricky. I am using 2 different types of tape and experiencing the same problem. with rmgi sm911 i push a 10K signal through at -20db on the vu meter and adjust the bias signal as I go from full attenuation to max pot, the level continues to rise. I then run out of pot before the level on my console level starts to drop. Basically I get most signal at full pot and cannot overbias. Same problem with Quantegy 499 and rmgi SM468.

I picked up a second oscillator board to see if the board was bad and got the same results with the second board. So either I have 2 bad oscillator boards, or that is just how these machines behave with this newer tape.

Any insights would be appreciated.

re: A77

Stumbled across this recently, and having had experience repairing my fair share of A77s I thought I'd give some input. I've had luck with modifying the power supply that the oscillator board is supplied from with a variable one and increasing the voltage slightly.

Worth a shot if your having issues. I've biased for SM468 on some A77s with that technique.

Hope that helps,


re: A77

I am converting a low speed playback card to high speed. I cannot read 2 values on the service manual. On or about page 67, there are 2 resistor values that a scribbled over:

1.007.785 : Equalization IEC 7 1/2/15

R811 = either 3.3k or 3.9K
R304 = either 53K or 33K

Anybody know what they are supposed to be.

re: A77

On a color photo of card 1.077.785 I can see that R811 is 3.9Kohm (if it was 3.3K the two first colors would be orange orange and it is orange white and then red as third color) and on my printout of relevant page I can see that first number of R304 is a "3" so it must be 33Kohm.

I am just in business to do the same "upgrade" operation, but I intend to make it switchable between NAB and IEC for rec. and play on both speeds (7.5IPS and 15IPS) using some extra relays and the speaker On/Off switch as a extra selector.
Revox never made this combination ...

Edit: I drop NAB as a recording option.

re: A77

Thanks so much for the information. I did guess 3.9k and 33K and made the mods a week or two ago. I would probably have tried different values if you had not confirmed my guess, so thank you for that. There is still a 2 or 3 db bump in high frequencies (>15K) after the mod, but the rest of the frequency range is pretty flat with the eq pot fully attenuated. Before the mod, the highs ( > 10K) where extremely exaggerated with the eq pot fully attenuated. I'd love a pic of the 1.007.785 board if you would like to send it to me at rob (at) leftofthedial (dot) com. Thanks again!

re: A77

Hi, I live in Sydney Australia and need to find someone who can repair a Revox A77Mk4
either here or overseas, yes I am desperate to get this machine back in operation.

Think the fault is in the left pre-amp board, very weak signal?

Any ideas welcome. Thanks

re: A77

Hi, Look on Ebay, there is a guy in Sydney called monypm , name PETER. He sells kits and he also repairs revox stuff as well. I want to use him but I am in melb, too far away. Hope this helps. Cheers. Gerry

re: A77

I know it's a little late to reply to your message of last April. I live in Canada and here is the link to reach the only Studer/Revox technical representative in the country:


I hope Roger will be able to help you.

re: A77

Hi Felix10,
I have an A77. I fix audio stuff especially tape decks. I live in the Southern Highlands. How we connect?

re: A77

I am Ali Shah, Hi!, may be I can help you if you could read the schematics.
Are u a technical.

re: A77

Brought one for my husband's Birthday and it does not work, we seem to be having a run of bad luck with reel to reel tape recorders and now have three that does not work. Have anyone got an idea of an electrical engineer that fixes reel to reel tape recorders around Northamptonshire, England. Thank you. Alison

re: A77

Hi Alison!

Since I'm from Germany, sorry, no, but I know some very good guys in North Germany, if you don't mind shipping the A77 to them. (BTW which type is it (mark 1,2,3,4 ? 2 track or 4 track ?))

They even sell repair kits and tuning kits for the Revox A77 and for the B77.

their site is at revox-online dot de

.. I don't know if this information is still of interest by now ..

Hope, you get it working, have 2 B77 working and 1 A77 in my repairing queue which I still haven't attended yet.



re: A77

I have seen a revox repairer in the Burnley, Lancs are on ebay who advertises repairs on Revox analogue decks, don't know if that will be any help?
Also taperecorder.co.uk may be of help.

re: A77

i got mine from germany and was damaged in shipping.
Main problem is all function keys can not lock in.
Can any one offer help?
Tks from hong kong

Chungalin's picture

re: A77

Function keys (<<, >>, Play, Rec...) do not mechanically lock after pressing. When you press them, a relay activates the function, but the key returns to previous position. This is normal. One possible cause of your problem is that there’s not a Remote Control jumper in the Remote Control connector (back-top panel). When there isn’t neither a remote control nor a jumper, the functions just work while you press the keys, but stop as soon as you release the key.

re: A77

So good that someone gives their time for no reward to provide information for people buying old equipment. For myself I have always wanted a Revox A77 but in my uni years I could not afford it, now in my 60's I can afford it and although its not a patch on my hi end hi fi its a dream come true - thank you. Andy New Zealand

re: A77

Thank you very much for this wonderful site.
I found out that the recorder does not work properly without
the dummy remote control plug. Where can I get one?
It seems to me that meanwhile I can operate the machine
by shorting poles 1 and 2 of the remote control socket.

MichaelJGamble's picture

re: A77

I made one up using two banana plugs which I now keep with the Service Manual. Michael (UK)

re: A77

My experience; I suggest replacing all the .047 caps on the relay board at least, on mine one had shorted it took out a resistor, machine went into play by itself and smoked the resistor. I also found a shorted electrolytic on the oscillator board. Indicator is a flashing end of tape light. Certainly a good design, well made and easy to service, the manual here was invaluable, thank you.

re: A77

Great thanks for the documentations!

Revox A77

Big thanks for your Manual download,it makes the mechnical and electrical more easy to use and service for me!
Best regards

Revox A77 Operating Instructions & Service Manual

Machine hasn't been touched for over 20 years. Cranked up immediately. Once I got the operating instructions works like new. Tape counter not working. Service Manual got the case open and the tape counter assembly out. Needed a 30mm toothed belt (not shown). (Off to Maplin for a 30mm drive belt (ok, for a cassette player). Everything now working fine. Only 400 x 10" and 7" tapes to check!!

The manuals are a real bonus. Thanks


Many thanks for your documents!
Perfect job.

Thank you

Thanks a lot for all your great work!

revoxA77/user manual

I just purchased a reel to reel /revoxA77mkiv[THANKS to this site I was able to receive operating manual] THANK YOU AGAIN.

Revox A77

Thx, for the manual and service manual if you whant see www. igoramp.it vintage amp .

from Siberia with love! Thank

from Siberia with love! Thank you! very use of a-77 and b-750 mk2


I just received A77 and a TEAC A3340S both in Super condition and where kept in climate controlled environments. I remember my Dad and My Grandfather both using these. They were both career Musicians. I need to find a Power cord for both.

Best Regards


me too, now i can repair my

me too, now i can repair my a77.
Thank you for upload manuals and etc...

Thanks very much

I can now work and repair my A77 :)

Ciao from Italy



Thank you very much!!! for service manual

is there an old version captan speed regulation board schematic?


i have a A77 which plays fine at 7.5 ips but can not work on 3.75 ips.

the switching signal of red AE1 (0/21 v) is available from switching board while switching to 3.75 ips but the speed is same as 7.5 ips.

the reading from Techno sensor is always the same as 1/0.6ms approximately.

in this A77. the capstan speed regulation circuit is discrete discriminator circuit instead the later monostable 555 circuit in Studer's service manual.

i would appreciated if i could receive an old version schematic to speed up my investigation.



Thanks so VERY much. My A77 has been setting up and now has a terrible distortion on record, still works fine on playback of previously recorded material. Don't know if I can fix it or not but with the manual I have a chance. Thanks again. rrc

check bias

Check if the bias is ok.


Grazie per il servizio reso a buon rendere


Grazie per i manuali messi a disposizione.

bigbozer's picture

Revox A77 Manuals & Brochure

Great service! I love it and use it all the time. Thank you Hi-Fi Engine.

A77 Manuals

I just have to say one thing. You made my day. God Bless!
Thanks a million.

great resource

awesome service and resource thanks again

Revox A77

Superb information

This website is not affiliated with or sponsored by Revox. To purchase A77 spares or accessories, please contact the company via their website or visit an authorised retailer.