Adcom 545II quirk?

Adcom535 · 20th April 2012, 09:08 PM

Interesting find with my 545II when hooked up to my three way speaker pair.
About five seconds following shutdown, the amp gives a very faint squeal through the left channel and about one second later the right channel exudes a slightly louder "squall" such as a tonearm stylus being drug slowly over an album,

Nothing loud or damaging but consistent.
The kicker, when my Polk speakers are substituted the issue disappears.
Only this particular amp has the issue with this set of speakers.
One modification to the three ways was changing the 10% Electrolytics to 1% PMPC caps. The enclosures both measure 6.85 ohms, sound very good and check out flat with an SA3050.
Just a quirk, weak component?
Lend me your thoughts.

djk · 22nd April 2012, 05:43 PM

Old caps can make for a 'squeeg' sound upon turn-off.

I usually add some small bypass caps (22µF~100µF) across the main filter caps when this happens, it usually kills the noise (and usually makes the bass sound tighter too).

PreCD · 24th April 2012, 11:01 AM

This is a common occurrence among the Adcom amplifiers. I have a GFA-555 with all new caps, including the filter caps, and it does the same thing. I disagree about the old ones being the culprit as mine did not start until I replaced them. Nothing to worry about.

djk · 24th April 2012, 11:46 AM

My Leach started doing this.

I changed the 100µF on the front end, and the 22µF on the output stage, left the computer grade main filter caps alone, and it quieted right down, the bass got tight again (I also changed the cap in the feedback loop).

I've added main filter bypass caps to other brand amplifiers that were making this noise and they quiet right down.

"Nothing to worry about. "

Your tweeters may tend to disagree.

Adcom535 · 24th April 2012, 03:11 PM

Thank you for the info.
Might do some research about replacing and upgrading the unit in the near future. I will likely ask for your input then as well.
Thanks again for taking the time with this basic issue.

20th April 2012, 09:08 PM	#1
Adcom535 diyAudio Member Join Date: Apr 2012	Adcom 545II quirk? Interesting find with my 545II when hooked up to my three way speaker pair. About five seconds following shutdown, the amp gives a very faint squeal through the left channel and about one second later the right channel exudes a slightly louder "squall" such as a tonearm stylus being drug slowly over an album, Nothing loud or damaging but consistent. The kicker, when my Polk speakers are substituted the issue disappears. Only this particular amp has the issue with this set of speakers. One modification to the three ways was changing the 10% Electrolytics to 1% PMPC caps. The enclosures both measure 6.85 ohms, sound very good and check out flat with an SA3050. Just a quirk, weak component? Lend me your thoughts.

22nd April 2012, 05:43 PM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	Old caps can make for a 'squeeg' sound upon turn-off. I usually add some small bypass caps (22µF~100µF) across the main filter caps when this happens, it usually kills the noise (and usually makes the bass sound tighter too). __________________ Candidates for the Darwin Award should not read this author.

24th April 2012, 11:46 AM	#4
djk diyAudio Member Join Date: Feb 2001 Location: USA	My Leach started doing this. I changed the 100µF on the front end, and the 22µF on the output stage, left the computer grade main filter caps alone, and it quieted right down, the bass got tight again (I also changed the cap in the feedback loop). I've added main filter bypass caps to other brand amplifiers that were making this noise and they quiet right down. "Nothing to worry about. " Your tweeters may tend to disagree. __________________ Candidates for the Darwin Award should not read this author.

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
JL 250/1 dc offset quirk	AKHeathen	Car Audio	8	8th February 2012 03:34 AM
re-Freshing an Adcom GFA-545ii	WithTarragon	Solid State	1	5th December 2007 05:34 AM
Quirk in Mullard 5-20 circuit	eduardio	Tubes / Valves	33	12th September 2005 08:06 AM
Modding Adcom 545II	StuartAmbient	Solid State	0	15th March 2005 01:00 AM
Adcom GFA-585 went bad - calling Adcom experts	hangguy	Solid State	14	24th December 2004 08:09 PM


	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

24th April 2012, 11:01 AM	#3
PreCD diyAudio Member Join Date: Sep 2011 Location: USA	This is a common occurrence among the Adcom amplifiers. I have a GFA-555 with all new caps, including the filter caps, and it does the same thing. I disagree about the old ones being the culprit as mine did not start until I replaced them. Nothing to worry about.

24th April 2012, 03:11 PM	#5
Adcom535 diyAudio Member Join Date: Apr 2012	Thank you for the info. Might do some research about replacing and upgrading the unit in the near future. I will likely ask for your input then as well. Thanks again for taking the time with this basic issue.

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