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Revox A77 problems Recorders, Players & Tape Machines
Old 3rd January 2011
  #1
Here for the gear
 

Revox A77 problems

I've finally got my hands on a 4track Revox A77! It hasn't been used a lot since the previous, and only, owner is an old widow. There was no sound when I got it but since I replaced some condensors it plays consumer tapes and sounds great.

The preamps sounds great and I've been using them a lot for tracking.

My problem is while recording to tape. Every once in a while I get high frequency drop outs on the left channel lasting for about 1-3 seconds. These are recorded to tape since they're there everytime at the same location.

I just cleaned the whole tape path but it keeps happening.

Any ideas from the more experienced tape people? Time to replace the record head?
Old 3rd January 2011
  #2
Lives for gear
 

Hi
If the thing works properly MOST of the time it will not be needing new heads.
I would suggest that it is a 'mechanical' problem with perhaps the tape not running 'true' or that the tape is so old it is 'shedding' oxide and gumming the head or even a damaged tape.
Since the bias oscillator and a fair amount of the electronics is 'common' to both left and right channels there is less chance of it being an electronic problem.
You could carefully swap the wiring at the head for left / right and see if the problem swaps over too. Start with the record head only. Put it back as it is now once you have tested it.
I would suggest NOT altering preset resistors for gain or EQ until you get nearer to finding what the real problem is otherwise you can get mightily confused!
Matt S
Old 3rd January 2011
  #3
Motown legend
 
Bob Olhsson's Avatar
 

The head connections on an A-77 are very fragile and subject to being pinched by the front panel and becoming intermittent. The pots used for alignment also become intermittent over time.
Old 3rd January 2011
  #4
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Quote:
Originally Posted by Bob Olhsson View Post
The head connections on an A-77 are very fragile and subject to being pinched by the front panel and becoming intermittent. The pots used for alignment also become intermittent over time.
So you're saying i shouldn't touch them, as Matt hinted above? Or are you saying that it might be good?
When I touch the pots for alignment with a screwdriver during recording I get disturbance on the left channel.
Old 3rd January 2011
  #5
Lives for gear
 

Hi
The presets are simply 'baby' pots often with no enclosure so will get dirty. It may be a good idea to make careful note of exactly where each is set then adjust them up and down a few times to clear the gunk then set them exactly as they were. You could even try measuring their position using a multimeter on resistance (unpowered of course) before twiddling them.
With the decline of in house maintenance gear is rarely recalibrated properly but will probably be near enough as a 'starting point' rather than random adjustments when there may be other issues going on.
Matt S
Old 3rd January 2011
  #6
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Thanks for the advice!
Old 3rd January 2011
  #7
Motown legend
 
Bob Olhsson's Avatar
 

I probably should have said the head wires are fragile. The pots are really cheap compared to a pro machine and the wiper can lose its ability to press hard enough on the carbon.

Another problem is that the ferrite erase head gap can chip due to temperature changes. This can result in it scraping oxide off the tape. Thankfully the head can be polished which will eliminate that problem.
Old 4th January 2011
  #8
Here for the gear
 

I redid the wiring from the machine to the tape head wires.
Seems it was one of the head wires on the playback head that was starting to give in. Once I redid that head wire I just get hum from that channel while playing.

Now I'm looking at the playback head wondering if there's a way to redo the head wire. Anyone ever done it? Seems very easy to replace tapeheads so perhaps I should get out there looking for a new playback head.
Old 7th January 2011
  #9
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Ok. So One of the head wires is broken and Im getting a New repro head . Anyone with experience of the nortronics heads? Im wondering how much of the sound of the revox is depending on the repro head . Ive found a nortronics head för 160 usd which seende reasonable.
Old 7th January 2011
  #10
Motown legend
 
Bob Olhsson's Avatar
 

The original playback heads have an amazingly flat frequency response especially in the low end.

I would first try to secure a new old stock play head from somebody who repairs the machines. When Studer discontinued factory service they sold a lot of parts to the folks they were laying off.
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