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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 27th Sep 2022, 7:19 pm   #1
Simondm
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Default Revox A700

I very, very stupidly gave away my copy of the A700 red book (I know it's on-line but the original had multi-coloured diagrams, etc.).

So I'm without the source to check, but I'm pretty certain it wasn't a daughter board* as such, but a complete revision of either the logic board or the record amp(s), or both. I"m pretty certain it changed the function of the two record enable buttons so they only switched when record was pressed, but it was all back in the late 1980s, and, although I still have the machine, I've had no real use for it since then.

I agree however that it was very good for its time, especially mechanically. It never damaged tape, and the chassis arrangements were copied across wholesale to the professional Studer B67 series, which remains one of my favourite machines to operate (and performs very well too).

At the time I discovered the issue, I looked at the possibility of upgrading to the later boards but it looked too complex for my resources at the time.

[edit] Ted I've just re-read your post. It sounds like you have a service history. Apologies if I have that wrong - it was a very long time ago.

*I'm not saying you're wrong - it might well have been a stopgap. There were definitely two revisions detailed in the service manual I had (bought directly from Bauch).

Last edited by Simondm; 27th Sep 2022 at 7:26 pm.
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Old 27th Sep 2022, 9:03 pm   #2
Ted Kendall
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Default Re: Revox A77 record/play question

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Originally Posted by Simondm View Post
At the time I discovered the issue, I looked at the possibility of upgrading to the later boards but it looked too complex for my resources at the time.
The original oscillator, 1.067.265 as I recall, exhibited the fault. I have seen early machines fitted with the additional board, which fitted between the oscillator card and the backplane, but this is not mentioned in the manual. The later card was 1.067.267, which eliminated the problem. I did rework three 265s to 267 spec, but it was a lot of work and required transistors from Bauch selected for high breakdown voltage. The boards worked, but weren't very pretty. The manual arrived quite late, I believe - it had revisions introduced near the end of production. There was an earlier booklet with just the schematics, which included that for an early capstan card which was produced when the TDA1000 chip was delayed.
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Old 28th Sep 2022, 3:03 pm   #3
Michael Maurice
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Default Re: Revox A700

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Originally Posted by Simondm View Post
By the way, Revox machines of that era are not the wonderful beasts they're often said to be:

I have a first-generation A700, which has some extremely nasty logic in its record switching. Studer revised the design, so later models don't do this, but the early ones are capable of putting audio without bias on the record head with the track record-enable and input selector switches in the wrong settings.

There's no need to press the actual record button for this to happen, and it both partialy erases the tape and overlays the recording with nastiness if you run the tape past the heads with that combination of switch settings.
Do you know in what way Studer revised the design? How can you tell if your machine potentially has this fault?
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