Hello good folks.
Well I am currently looking for some help with a 555 I purchased recently.
It powers up alright on the DBT, the bulb dims to nearly off.
DC offset is reading 49mv right channel, 46left channel. Turning the adjustment pots is very finicky, and I really cannot get it much better (this is on through the DBT).
With NO inputs connected, left channel has a significant buzz (like a very loud bee).
Right channel is fine.
Both channels play music.
All fuses look good. Everything looks in good shape, nothing is burned. I have replaced the electrolytic capacitors on the board with exact replacements no change. I also changed the driver transistors with high capacity ones (suggested). No change after that alteration.
I am uploading a video of the symptoms, should be on here in a little while.
Any help would be great. I called the adcom support and the guy was completely no help at all....
Thank you.
Walker
Well I am currently looking for some help with a 555 I purchased recently.
It powers up alright on the DBT, the bulb dims to nearly off.
DC offset is reading 49mv right channel, 46left channel. Turning the adjustment pots is very finicky, and I really cannot get it much better (this is on through the DBT).
With NO inputs connected, left channel has a significant buzz (like a very loud bee).
Right channel is fine.
Both channels play music.
All fuses look good. Everything looks in good shape, nothing is burned. I have replaced the electrolytic capacitors on the board with exact replacements no change. I also changed the driver transistors with high capacity ones (suggested). No change after that alteration.
I am uploading a video of the symptoms, should be on here in a little while.
Any help would be great. I called the adcom support and the guy was completely no help at all....
Thank you.
Walker
Ok good people, here is the video I made today.
YouTube - video-2011-04-11-16-29-12 ADCOM 555 Test.mp4
Please excuse the videography, I was using my phone.
Walker
YouTube - video-2011-04-11-16-29-12 ADCOM 555 Test.mp4
Please excuse the videography, I was using my phone.
Walker
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I switched the main power caps from the right side to the left. Yes I maintained the correct polarity, and started it up on the DBT.
Now in stereo both channels hum VERY loudly, and I am getting 140mv DC at each output.
When switched to bridged only the right channel makes noise (also very loud), and the left is silent.
Someone tell me to take this to a shop please.
Walker
Now in stereo both channels hum VERY loudly, and I am getting 140mv DC at each output.
When switched to bridged only the right channel makes noise (also very loud), and the left is silent.
Someone tell me to take this to a shop please.
Walker
Make up a pair of RCA connectors as shorting plugs (not connected to
anything else) and put them in the inputs. What noise do you get?
Nelson,
Does that apply to the 1 Gen 555s. Mine is below:
An externally hosted image should be here but it was not working when we last tested it.
The reg is not part of the Adcom circuit. That looks like the Kit Ryan regulator from Audio Amateur.
Dudeman, did you try what Nelson suggested? Since he designed that amp, he should know...
Nelson,
Yes I understand that. I guess if I would have thought before I asked that question it would have dawned on me that it would work on any amp. Thank you for the reply. I am looking forward to firing up this vintage 86' amp when my 565 gets here tomorrow. I am really tickled that I got one of the early Adcoms that you designed. Everything is still solid except leaching of thermal compound from the rectifier bridges and output boards.
Kevin
Yes I understand that. I guess if I would have thought before I asked that question it would have dawned on me that it would work on any amp. Thank you for the reply. I am looking forward to firing up this vintage 86' amp when my 565 gets here tomorrow. I am really tickled that I got one of the early Adcoms that you designed. Everything is still solid except leaching of thermal compound from the rectifier bridges and output boards.
Kevin
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Bump. I'm having a bit of noise/buzz from the left channel of my original GFA-555. Pretty faint but louder than the right channel and audible in a quiet room from 10 ft away. I bought the amp around 13 years ago, it had one power cap replaced at the time.
I intend to run this pretty hard for PA use in the near future. I'm guessing it would be smart to re-cap the electrolytics, but I'd like to resolve the buzz before dumping time and money into it as a project.
Any guesses if the buzz will get worse as I run the amp hard......?
I intend to run this pretty hard for PA use in the near future. I'm guessing it would be smart to re-cap the electrolytics, but I'd like to resolve the buzz before dumping time and money into it as a project.
Any guesses if the buzz will get worse as I run the amp hard......?
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So the the recap has a pretty good shot at resolving the buzz? I was going to check the DC offset and adjust the bias for starters. Have downloaded the service manual.
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