Snap, Crackle, Pop... it ain't rice krispies.

[dc55110]

My Adcom GFA-555II in the past week started making the aforementioned noises at random times while no signal was being feed to it out of the left channel. The sound is only in a high frequency register and only last a few seconds. As I said it happens at random, cold or hot, night or day, etc. The amp is clean inside and out, a quick peak under the hood only reveals only a small bit of dust on the toroidal transformer. Any guess as to the source or cause of the problem?:confused:

[LessisNevermore]

Almost thought this was another vinyl thread.:p:D

Sounds like maybe an interconnect cable going south.

[dc55110]

I tried another amplifier, every connection was still the same, no breakfast cereal coming out the speakers.

[obieone]

I'm NO guru but, How old is the unit? May be time for new caps?

[apphd]

I tried another amplifier, every connection was still the same, no breakfast cereal coming out the speakers.

Did you go back to the Adcom and have the problem return? If it was a connection problem..........it may be gone now.
If it came back, you could switch the R&L at the amp, first I would swap the speaker outs, if the problem is still on the left swap the L&R inputs. Then swap the L&R ICs between the amp and pre. When you say "noises at random times while no signal was being feed to it out of the left channel" are you saying input devices were off, or just no material being played? I'm anal about confirming a problem but if through all this the problem stays with the left then chances are it is something with the amp. If you already knew this and was looking for some more specific things to check on the amp hopefully some Adcom owners can help.

[dc55110]

Did you go back to the Adcom and have the problem return? If it was a connection problem..........it may be gone now.
If it came back, you could switch the R&L at the amp, first I would swap the speaker outs, if the problem is still on the left swap the L&R inputs. Then swap the L&R ICs between the amp and pre. When you say "noises at random times while no signal was being feed to it out of the left channel" are you saying input devices were off, or just no material being played? I'm anal about confirming a problem but if through all this the problem stays with the left then chances are it is something with the amp. If you already knew this and was looking for some more specific things to check on the amp hopefully some Adcom owners can help.

Yeah, I've narrowed it down to the amp. I've swapped speakers, amps, speaker cable, interconnects. Only constant is the Adcom. I figure it is the caps (although they look excellent, no distortions in shape or any substances being emitted). I just don't know how to test that it is the caps or if there is something else in the amp I'm overlooking. I'm just curious if anyone else has had this issue, if so what was the root problem.

[leroyjr1]

I've had numerous 555II's and never a problem at all. You don't here of 555's having problems that often but it's an electronic device so it's possible.

[dc55110]

Any advice? Bueller? Anyone?

[ben62670]

Either caps, or fusible resistors. Both of those get a bit noisy before they go. You should just sell it to me for $100, and put the money aside to get another amp.

Edit: If you are poking around in the amp make sure the big caps are completely discharged. Take a volt meter set for DC, and measure for voltage on the big caps. Lots of DC volts hurts more than 120vac:o

[dc55110]

Either caps, or fusible resistors. Both of those get a bit noisy before they go. You should just sell it to me for $100, and put the money aside to get another amp.

Already have the new amp (see http://www.polkaudio.com/forums/showthread.php?t=87982) and I do plan to sell the Adcom. I would like to fix it if the job isn't too hard, my desoldering/soldering skills are proficient. My biggest problem is tracking down the problem component in the signal path, with my limited diagnostic tools. I'm also having trouble tracking down replacements for the big 15k caps.
The amp still, while playing, sounds great. It is only while idle that the cereal makes its appearance.

[ben62670]

The big caps are fine. I may have the service manual for that amp on my other puter. If you call Adcom they will send it to you via PDF the same day. Look for the fusible resistors on the input boards. Off the top of my head there are 2 100r's, and 2 10r's that tend to go. Also the amp is common ground, but the negative feedback loop gets stressed if the grounds are not tied together when running SDA's. Test the fusable resistors on the output boards also. I replaced them on an Adcom I used to have, and it cleaned up the sound quite a bit. I used 1% Yageo metal films. That simply upgrade cleans up the sound a lot.

Edit: BTW I was being a wise ass when I suggested that you sell me the amp for $100.

[dc55110]

Edit: BTW I was being a wise ass when I suggested that you sell me the amp for $100.

I figured you where... Thanks for the input, its greatly appreciated.