Another GFA-555 With high dc offset - diyAudio
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Old 21st July 2010, 04:21 AM   #1
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Join Date: May 2010
Location: Florida
Default Another GFA-555 With high dc offset

I am at a loss right now as to why I have such high dc offset at the output of my GFA-555 (not a MKII). One channel the right has 22.7mv and the left has 268.4mv. I rechecked the BIAS and have it set at -16mv as per the service manual. I have checked everything on the input board and everything appears to be fine. The amp sounds fine other than just the high channel sounds a little distorted. Has anyone had this problem before with this amp? I did check all the outputs and all appear fine and have never been replaced. Pre-drivers fine also, at least they appear fine no shorts, open or high resistance. I,m driving a pair of Snell's and hate to see them smoke. I have one GFA-555 and one GFA-555 MKII Bi-amp'ed. I also noticed that the BIOS current is not stable it moves from 16mv-18mvand dosn as low as 10mv. The current across the outouts are not all the same either and range from 21mv~18mv. Could this be the outputs in that ch are going bad even though the messure fine?
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Old 21st July 2010, 05:50 AM   #2
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Join Date: May 2010
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I see this I may have put this in the wrong forum. I should have put this in Solid State, mod could move if needed.
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Old 22nd July 2010, 12:51 AM   #3
llwhtt is offline llwhtt  United States
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Join Date: Jun 2008
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I wonder if this particular model has the dreaded leaky capacitor disease? I think DC offset was the first problem to show up. Check the circuit boards for evidence of electrolyte around the capacitors. Anatech (Chris) on this forum is the one you need to get in touch with. He was a Adcom servicer in Canada. He can fill you in on everything that needs to be done if that is the case.

Craig
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