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Help diagnosing my Adcom GFA-535

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Hi, all!

 

Today I've run into a problem with my GFA-535. When I went to switch back to it from a different amp, I noticed an unusual buzz start to come from my subwoofer when I turned it on. Not wanting to risk my Heresies in case something was wrong (glad it has speaker selectors!), I plugged one of my B-10s into the left channel on the other set of outputs. Once patched in, it revealed a loud, nasty static buzz (I also tested the other channel.)

 

It only does it when it has something connected to either input. It could be a bare wire and it happens. I connected my iPhone as a source when trying to single out the amp from the preamp and it still did this, without seeming to react to the signal from the phone. It also seems to certainly cause feedback back through the inputs, as my subwoofer only buzzed when the amp and preamp were connected.

 

Now, a few things that happened recently. First, one of the metal rings surrounding the right channel RCA plug had come out when unplugging it recently, leaving just bare plastic. I always assumed these were cosmetic, since the other one was never there (I received the amp that way) and it was never a problem.

 

I also I believe I plugged the pre back in with the preamp still on (and the amp off).

 

How could I go about diagnosing this, and does it seem like something I could fix myself? I like the 535, and while it would be fun to shop for a new amp, I wouldn't be happy to trash this one. Thanks!

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Thanks, everyone! I got the ring back on and it fixed everything. I'm not sure why it only needs the one (the other channel hasn't had one in the time I've had this amp,) but it works. I'd forgotten how much better it sounds than the HT power amp I'd been using!

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While the amp is dual-mono, the preamp will have a common ground, so only one ground for the input signals will generally suffice.

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Glad you've got it going!

 

I've got a NAD integrated amp that has the same 60hz tone. Mine started with a lightning strike. Clipping light now stays on. No part of the amp will work without the background noise. Sheeze, where to start? I'm guessing power supply. Maybe a power supply cap has shorted to ground? Any suggestions appreciated. 

 

 

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25 minutes ago, JL Sargent said:

Any suggestions appreciated. 

Send it to Paul Hovenga;)

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5 hours ago, CECAA850 said:

Send it to Paul Hovenga;)

 

I paid like $50 for this on Ebay, so sending off for repairs might not make much sense. However, looking for a fat $5 cap might be worth it. :)

 

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lightning strike just might be the kicker here... I would open it up and look for a burned up ground trace. If it is working and humming, something that was (is) connected to it may have burned up a signal ground trace.

 

I say this because it is working. If it was a main ground in the amp or supply, It would not work.

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Thanks Paul, I'll give that a try today. I actually found a missing ground trace in a microwave control board 10 or so years ago after another lightning strike here. Jumpered that out and all was well again with it.

 

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With Paul's troubleshooting suggestion I've separated this NAD 3130 integrated amp from all other equipment and taken it to another room and I can report the 60hz tone is gone. That's the good news. This remaining issue is that one channel is about 1/2 volume of the other? I don't really hear any new noise though? Never has been a dead quiet amp for that matter. A visual inspection reveals nothing.  No surface mount technology present on this one. All traces look good. No fat caps. The amp has 4 main transistors. 2) 2N3055 and 2) MJ2955. Maybe a transistor has failed?

 

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The offending channel continues to go down in volume. Now just a whisper out the L speaker.

 

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That would be a dirty relay. Flip it with your finger, and I bet you can make it do crazy things. You can pop off the cover of these relays carefully, and clean the contacts.

 

Now you get to figure out what component is humming! Preamp most likely, same scenario, check the jacks and the traces related to them.

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Thanks for your help Paul. I'll have to troubleshoot more another time. Happy New Year to you.

 

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