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In Reply to: RE: What's this soldered to my Revox A77 repro amp PCB? posted by lowpoke on July 24, 2012 at 23:44:00
You should try putting your old boards back in. If they work as before, contact the folks you got the new boards from.
What made you think it was the repro amps that was causing the problem before? The symptoms you've described sound head related.
Did you run a known good test tape and adjust the heads (after a thorough cleaning of the entire tape path)?
Getting to the bottom of what is the problem with the new boards working on your machine could be a real hassle. I'd be positive that it isn't something else before spending too much time and patience on the repro boards.
Follow Ups:
Ironbut, the cap was on the pulled boards, not the new ones, if I read the OP correctly.
Thanks for your reply ironbut. The heads are in excellent shape, showing virtually no sign of wear. I have received a reply from the guys I got the boards from that makes sense:
Hi , first you have to fix the potentiometer ,the small black part, in the right position. The parts on the back side are used for different heads. Revox build in , for round about 1 and a half year heads with different impededanc and mH , so they have to correct this with the parts on the back side of your boards. So please try to fix the poti in the right position.
Looking at my old boards, there are no potentiometers, so the part on the backside was a substitution. Any idea how I should adjust these pots? I've not heard of this before.
Show us what ya got: Homebuilt Hi-fi
If the pots are part of a modification done to the board and aren't found on your service manual, only the folks who modified the boards can tell you what they're for and the procedure for correct adjustment.
BTW, many electronic measurements are assuming that the heads have been correctly adjusted. You adjust them to get maximum and equal output levels and flat frequency response.
Brand new heads need to be adjusted and can be off by as much or more than a totally worn head.
If you've never adjusted heads, don't have the test tape ( a special tape made for this purpose) or a dual trace scope, you should take the machine to a qualified tech.
Hey guys, thanks for your help so far. The potentiometers on these new boards were just turned down to nothing. Simply turning them up so to speak, has of course enabled audio on both channels. My old boards didn't have pots and compensated for this by the cap soldered on to the rear. At least this is what the supplier of the new boards told me.
Top end in left channel is still lacking compared to right, so this needs looking into. as suggested already, heads probably need alignment.
Show us what ya got: Homebuilt Hi-fi
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