Another GFA-555 With high dc offset

embrown057 · 21st July 2010, 04:21 AM

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?

embrown057 · 21st July 2010, 05:50 AM

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.

llwhtt · 22nd July 2010, 12:51 AM

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

21st July 2010, 04:21 AM	#1
embrown057 diyAudio Member Join Date: May 2010 Location: Florida	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?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Another high DC Adcom GFA-555	fredlf	Solid State	663	12th April 2011 03:14 PM
Adcom GFA-555 mk2 left slight cracking in high freq	lga775	Solid State	2	4th December 2010 11:30 AM
Help! Adcom GFA 585 DC High offset problem	birdyman	Solid State	2	29th April 2010 01:44 PM
Adcom GFA-555 Feedback DC-Blocking Cap?	EchoWars	Pass Labs	14	14th April 2010 07:12 PM
Adcom GFA-555II with DC Offset	sjdemark	Solid State	19	28th February 2009 01:33 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

21st July 2010, 05:50 AM	#2
embrown057 diyAudio Member Join Date: May 2010 Location: Florida	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.

22nd July 2010, 12:51 AM	#3
llwhtt diyAudio Member Join Date: Jun 2008	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

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)