Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

ADCOM GFA-565 DC Offset Fluctuation
ADCOM GFA-565 DC Offset Fluctuation
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
Thread Tools Search this Thread
Old 4th March 2011, 12:39 PM   #1
retrex is offline retrex  United States
diyAudio Member
Join Date: Jan 2011
Smile ADCOM GFA-565 DC Offset Fluctuation

Sorry to rehash this but I have read the threads I could find on the subject and never really got enough info to quell my concerns. I have just purchansed a pair of GAF 565s, one going back to seller to rectify a hum and a .5V DC offset issue, the other with a DC Offset that will not settle down to a stable value. It is fluctuating between -4mV and +7mV, constantantly cycling and never resting on any one value for any period of time. I tested with pre hooked up, no signal, speaker attached, after about a 20 min warm up of playing and 10min rest w/no signal. I have a GFA 585 that does not exhibit this behavior so I am a bit worried. Can someone in the know please let me know if I have reason to be concerned? All replys are welcome and appreciated. Oh and first post to forum after many hours of enjoyable reading. Thanks.Click the image to open in full size.
  Reply With Quote
Old 7th March 2011, 06:20 AM   #2
amadork9 is offline amadork9  United States
diyAudio Member
amadork9's Avatar
Join Date: Dec 2010
The problem:

There could be few bad leaking electrolytic capacitors on each input board. The electrolyte from bad capacitors spills over the board.
The electrolyte is a conductive liquid which causes servo DC and differential circuits to malfunction. At this point the amplifier can not properly control DC voltage at the speaker output terminals, which has to be about 0 volts without input signal applied. As a result you notice that the cold amplifier make loud turn on/off pop or has distorted sound, but works fine after warming.
On the other hand, the electrolyte is corrosive liquid and can cause damage of some parts on the board.
As a consequence, the amplifier gets dangerous voltage at the speaker terminals, up to 70 volts, and can destroy the speakers.
This process is very slow and can take several months before the amp blows the speaker, so you have a chance to notice the problem and save your lovely speakers.
Simply check DC voltage across the speaker terminals without speakers hooked up and without input signal by using a multimeter.
When you turn on the amp, the DC can jump up to 0.2 volts, then it slowly goes down. In 1 minute it must be stabilized at 0-30 mV (less than 0.03 volts).
If your amp has more than 30mV DC, it must be repaired ASAP
  Reply With Quote
Old 9th March 2011, 12:34 PM   #3
retrex is offline retrex  United States
diyAudio Member
Join Date: Jan 2011
Default Adcom DC Offset Fluctuating

Thanks for the repy amadork9. Yes I was aware of the leaky cap issue and solutions with regard to rectifying it. I was trying to get a sense of whether the fluctuation is a symptom of the the same problem and the degree of damage, if any, the variance poses to operation of the amp. And if is not a problem now when will it become an issue, if at all? Can I monitor the DC Offset periodically and move to correct above a certain level? I believe I still have the option to return the second unit for repair as well but I am trying to get a sense of the seriousness of the problem before I go down this path. I don't have a problem working on electronics, EE background, but I still don't own it fully in the sense that I view it as a good transaction and accept the deal as is. I have only listened to the amp breifly due to the other one being sent back for repair soon after I received them, but it did sound ok. I am just going to the experts for some additional insight and support.
  Reply With Quote


ADCOM GFA-565 DC Offset FluctuationHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
ADCOM GFA-555 Output DC Offset Voltage Measurements PB2 Solid State 31 29th July 2011 07:08 PM
Help! Adcom GFA 585 DC High offset problem birdyman Solid State 2 29th April 2010 02:44 PM
Adcom GFA-565 again, fluctuating DC offset haash Solid State 5 4th May 2009 04:08 PM
Adcom GFA-555II with DC Offset sjdemark Solid State 19 28th February 2009 02:33 PM
Help with Adcom GFA 565 DC offset? craiggoff Solid State 2 11th February 2006 11:39 PM

New To Site? Need Help?

All times are GMT. The time now is 08:38 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio