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Old 31st January 2008, 01:58 PM   #1
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Default Adcom GFA-555II

I just purchased a new adcom amp. When I power it down, after the caps discharge, it pops a couple of times through my speakers. I contacted the seller and he told me that ALL Adcom amps do this. I have owned many high end amps and have never heard of such a thing. My BS meter is off the chart right now, could anyone confirm this behavior? Where I come from pops is usually bad.
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Old 31st January 2008, 02:25 PM   #2
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One thump is considered normal. Not multiple pops.
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Old 31st January 2008, 02:29 PM   #3
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Default correction

What I was trying to say that the GFA-555II is new to me. I purchased it on ebay and looks and sounds brand new. Also the popping noise happens about 20 seconds after the power switch is turned off. Sorry, been up all night doing taxes.
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Old 1st February 2008, 01:11 AM   #4
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Bad caps on the circuit board.

If any have leaked, the boards will have to be cleaned with an ultrasonic cleaner.
Candidates for the Darwin Award should not read this author.
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Old 1st February 2008, 02:51 AM   #5
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Default popping gfa-555II

Checked out all the caps, no sign of leakage at all, and the boards look brand new. Any other suggestions? I guess I can just leave it on and see how high my electric bill can go, kidding of course. I guess I should probably do a proper cleaning though. The popping noise is really not that bad, it sounds like a muted version of Yamaha's test signal on their surround program. (YPOA, I think) That's the best description I can come up with. However, I am not afraid of preventative maintenance. From what I have heard, Adcom tech support is good, but I am open to suggestion for better replacement parts. You guys seem to be quite a bit sharper than tech support I have dealt with in the past. I sincerely appreciate the quick responses from all of you.
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Old 1st February 2008, 03:00 AM   #6
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I have a GFA-6000 that did a similar sound when I shut it off. It would make a slight buzzing or fffttting noise around 10 to 20 seconds after I shut it off. It has done this since I bought it in 1996. This is the main caps in the power supply discharging, so I don't think it is an immediate issue. However, since they haven't made the 555II for 10 years or more, you will want to keep an eye on them and perhaps check them out with the proper test equipment.
If you contact Adcom, let us know how it goes. I was talking with the shop here in my area that used to be a dealer of Adcom. They dropped them a couple of years ago. There were two reasons. They said that Rotel was outselling Adcom by 4 to 1 in the area, and they also said that Adcom is now on it's third owner. This owner has relocated the company from New Jersey to Arizona. From what I was told it is now owned by a group of investors. If this is true, this is usually the first step towards ultimate mediocrity of a brand. Investors are usually more concerned with money then product quality and long term reputation of a brand.
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Old 1st February 2008, 09:32 AM   #7
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Default gfa-555II popping

Cleaned everything, dusted it off, installed MUCH better interconnects and lo and behold the pops are almost inaudible. Talked to Adcom and they told me that it is common. Just for grins, I added a Hafler P300 and bi-amped a pair of custom made Toby tall satellites (I have known Toby for about 28 years) If you haven't heard of him, I highly recommend checking out Incredibly talented man, Plays electric bass for the Fort Worth Symphony, and builds the best enclosures for home as well as cars you can find in the D/FW area.
Anyway, it only took the police about 5 minutes to let me know that they could hear every note from the new Tool album I was playing. Came in, looked at my system, smiled, and asked where they could get speakers like mine. I guess being 50 actually helped me from getting a ticket. (very unusual in Texas) I really had doubts about mixing the two amps, but I have to tell you I was shocked. I want to thank you for your response in this matter, everyone has been great.


Cary Crager
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Old 20th December 2011, 02:21 AM   #8
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Hi Cary - Sorry about jumping in so late on this but I too have this issue with a 555-II and with it connected to a set of fully restored QLS-1's I was worried about the ribbons mostly. I wrote Adcom about it and their reply was that the bleeder resistors needed to be replaced. The pops on mine start at about 14-15 seconds after powerdown and are not equal on both channels - I get about 6 pops on the left and 2 on the right at different intervals - not really loud and not thumps/no woofer excursion. They said that if they were different on each channel, it was definately the bleeder resistors. I'm going to be diving in with a refurb/recap/mod soon on it and will take care of this then. Everything else with it's fine (great) though. So far after many power cycles, my tweeters still live, so I'm guessing they'll be fine until then (it still pains me to hear those pops though! - every single time) Interesting about the cleaning (mine's pretty spotless inside and out) - did you do anything else after that or are they still doing it/did they get any worse?
Hope that helps any...
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Old 1st March 2012, 05:02 AM   #9
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All ADCOM amplifiers from the classic GFA series "pop" upon power on/off conditions. It should not pop more than once upon power on but on average most will pop once or twice on power off. This is due to several things during power off: there is no speaker disconnect relay to isolate the speakers, the main power supply capacitors are discharging, and the DC servo circuit is now inoperative due to lack of needed DC voltage to function. You can easily see this for yourself by attaching a voltmeter to one set of output terminals. When you first power the amplifier up, the DC offset will shoot up before slowly coming down to normal (<100mV) as the DC servo circuit operates. Upon power off, watch the DC offset on the rear terminals as it ramps quickly upwards to many hundreds of millivolts before coming down as the main power supply capacitors discharge. When your speakers are connected, usually it is the woofers that are providing the fast discharge path for the high DC offset resulting in the pops you hear.
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