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Old 14th January 2002, 08:23 PM   #1
diyAudio Member
 
Join Date: Jan 2002
Location: San Diego
Question Adcom Amp Prob

I have two Adcom GFA-545 mk II amps; when I
power them down, they make "swooping" sounds through the speakers (starts high freq and
ends low freq).

One just swoops, the other swoops plus makes popping sounds. Note: my system is bi-amped:
one amp per channel.

I have been told that this symptom:

"indicates an imbalance of the +ve and -ve
power rails upon shut down. Check the amp's
power stages, before they blow out your
speakers one day"

How can I adjust my amps so they are aligned
properly?

Specific details required: I am not a tech, but
I work at an electronics calibration lab and
have access to test equipment.

Thanks,
Mark Buckles
San Diego
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Old 14th January 2002, 08:58 PM   #2
PassFan is offline PassFan  United States
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Join Date: Aug 2001
Location: Central FL
Mark:
It is hard to troubleshoot over the wire. I usually don't attempt to fix my own stuff without a service manual. Adcom will sell you a service manual which will give you test voltages all through the circuit. All you will need is a voltmeter to isolate the problem. I had a GFA-535 that I purchased a service manual for, but I sold it with the amp. Good luck
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Old 14th January 2002, 09:23 PM   #3
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Join Date: Jan 2002
Location: Ingolstadt, Germany
Hello Mark,

I think it is right what you have been told, and what PassFan wrote also.
One simple suggestion from me: check the supply caps, as one side may have weakened over the time and so one rail faints while the other is still present. May be that this would alter the specified conditions of some transistor stages.

Hope this helps
AndyM
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Old 14th January 2002, 09:48 PM   #4
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Join Date: Jan 2002
Location: San Diego
Default Adcom Amp Prob

Thanks to PassFan and AndyM for your replies!

I dug through my manual drawer, and lo! - I have
the service manual for the GFA-545. I shall try
to check the specified voltages without zapping
myself.

Regards,
-Mark
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