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Adcom GFA-565 Capacitor Replacement

I own two Adcom GFA-565 mono amps. One began to thump while in use, so I brought both to an authorized service center. Tech tells me that he is finding DC across speaker leads on both amps, and that oversize capacitors need replacing and that he thinks Adcom no longer makes them. I asked for alternatives, he said "they make great anchors". Is there a place I can obtain original or acceptable substitutes for the capacitors? THANKS!
schmengie_mcs7750
pauly
1,012 posts
 
Greg sez

“Come on, Paul, tsk, tsk. Lytics are fine”

I thought this was an “audiophile” forum ;-)

“Easy to diy -- BUT if in doubt, go to technician.”

The tech is telling him “boat anchors” remember? Best stay far away from that tech – sounds like a shady character.

“It has to be electrolytic for the main power supply caps”

Nope – I used motor run caps in power supplies and they are the bomb. For the adcom there prolly won’t be enough space to go this route though.
tfong
1 posts
 
The thump is caused by a dc voltage offset (as you said dc accross the speaker). This offset is usually caused by the leakage of electrolytic capacitors accross the voltage reference diodes on the driver board. The capacitors are 25volts, 220mf, cost about 79 cents a piece (there are four of them to replace). However, when this happens, usually the reference diodes (6.9 volt temp compensated Zeners) or the bias control transistors (MPS-A63 and MPS-A13) also need replacement. Your technician is full of it, the power supply capacitors are very durable, and most likely are not the problem. By the way, the power supply capacitors, 120 volts, 36000mf, are very expensive, about $90 a piece, and are difficult to find. Your best solution might be to search on the web, e.g. Ebay, for Adcom repair services, which can cost you a couple of hundred bucks per amplifier.
gander2's avatar
gander2
2 posts
 
I just bought Adcom GFA-565 monoblocks and they thump the speakers on startup, but after that I'm not finding any problems. Is this a problem that can be fixed? According to Adcom, this is "normal" for these amps (yes I have that in writing). Is this true? And is this different than thumping in use, as noted above? I would like them NOT to thump on my Maggies.
Thanks,
Gary
power_hungry
3 posts
 
I found this article about the amps that really explains the issue with these amps (both the GFA-565 AND the GFA-585) better than any of the posts here:

http://www.jazzfest.tyrell-corp.com/stuff/repair_adcom_gfa-565_gfa-585.htm
strader
1 posts
 
when I change out the leaky electrolytic capacitors between the reference diodes on the driver board, is there a certain type that I want to go to?
you mentioned the reference diodes (6.9 volt temp compensated Zeners) and the bias control transistors (MPS-A63 and MPS-A13 will need to be replaced? any type or part number I should go with for the replacements? thanks a bunch
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