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Adcom GFA-2 Amp Repair


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#1 The Monkey

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Posted 14 November 2010 - 10:22 AM

So it looks like the old B&W speakers are ok, which leaves pretty much only the amp as the culprit. Specifically, it seems like one channel is problematic. The sound it puts out sounds very very muffled, distorted, and scratchy. I opened up the amp and didn't see anything that to my untrained eye appears to be obviously kablooey. However, I did note that one of the fuses on the board looks different than the others. It's not blown but could that be it? Anyone see anything else?

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#2 Yikes

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Posted 14 November 2010 - 10:50 AM

A fuse being blown can sometimes cause your described symptoms, but having a different fuse in one location (That's not blown) would not. Did you check the fuses with a meter, or did you eye-ball them? Sometimes a fuse looks good when it's not.
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#3 The Monkey

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Posted 14 November 2010 - 10:54 AM

No meter here, so I just eyeballed them. I'll try to replace the fuses as a first step.
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#4 Yikes

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Posted 14 November 2010 - 10:59 AM

Have you isolated it down to one channel?
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He's a moderate Corporatist.

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#5 spritzer

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Posted 14 November 2010 - 12:22 PM

Is there an output relay? I can't see it but a bad connection there would account for the issues you are describing.

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#6 Pars

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Posted 14 November 2010 - 12:30 PM

The far right fuse looks a little different, but doesn't really mean anything.

Saw one thread on diyaudio regarding these, something about loose RCA grounds:
Seeking help- something caused HUGE noise - diyAudio

Do you have a meter, but just not there? At a minimum I would check the DC offset on both inputs if you have access to a DMM. And I have gotten schematics for free from Adcom just by asking them via email (if it comes to that).

EDIT: A bit of info in this thread as well (see post 34)
http://www.diyaudio....nsformer-3.html
And follow Doug's advice :)

Edited by Pars, 14 November 2010 - 12:36 PM.

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#7 dsavitsk

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Posted 14 November 2010 - 12:32 PM

No meter here, so I just eyeballed them. I'll try to replace the fuses as a first step.


Just swap them from channel to channel, if the problem moves, you've found the issue.

#8 The Monkey

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Posted 14 November 2010 - 01:24 PM

I replaced the fuses on the suspect side. Problem persisted. I then replaced the single fuse that's at the bottom of the picture. Success!

Then the problem returned. :(

Replaced that fuse again. No joy. Problem back where I started. Does this seem like a grounding issue? This is starting to annoy me.

EDIT: also blew out some dust with some compressed air.
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#9 EdipisReks

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Posted 14 November 2010 - 05:53 PM

the sound spider has likely escaped from the amp. you'll need to go to Ultima Thule and barter with a Gorgon to find a new sound spider.
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#10 Salt Peanuts

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Posted 14 November 2010 - 06:29 PM

What does a sound spider look like?

#11 The Monkey

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Posted 14 November 2010 - 06:31 PM

I don't know, but based on its droppings, I don't want to find out.
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#12 EdipisReks

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Posted 14 November 2010 - 07:13 PM

What does a sound spider look like?


9 foot leg span, with spinning spiky stingers, but it folds up to look like a pair of un-matched FETs.
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#13 The Monkey

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Posted 15 November 2010 - 02:42 PM

:shudder:
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#14 EdipisReks

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Posted 15 November 2010 - 03:00 PM

but once you catch one, and defeat it in a game of chess, and then a game of spider wrestling, you can force it into the amp, which will then start working again!
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#15 luvdunhill

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Posted 15 November 2010 - 05:52 PM

but once you catch one, and defeat it in a game of chess, and then a game of spider wrestling, you can force it into the amp, which will then start working again!


I'd choose a slightly more intractable game, just in case...

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