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Old 2nd October 2008, 03:23 AM   #1
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Join Date: Sep 2005
Default Audiolab 8000A fault

(I've searched for information on this fault but haven't come up with anything concrete).
I've got an Audiolab 8000A which crackles for a short period following power-up when the volume control is used. I'm pretty sure it's not the pot, as it's fine after 30 seconds or so. The crackle is a bit disturbing (to me at least) as I suspect that something is on its way out.

Has anyone got any idea where to look? PSU? Dried out cap? dry joint? I'm thinking that perhaps there is some DC current on the pot which shouldn't be there - am I barkig up the wrong tree?

I've seen the circuit diagram posted on this site but as far as I can tell it doesn't show the volume control which I guess is prior to the power amp input.

I haven't got around to measuring the rails yet but I will do so, however as this fault seems only to occur during power up from cold, I think it may be hard to capture it as it happens in real time.

Regards,
Dave.
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Old 2nd October 2008, 11:27 AM   #2
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I suspect the noise must originate from the volume pot if it only happens when the pot is turned.

Is the noise level constant regardless of whereabouts the pot position is when it's moved?
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Old 2nd October 2008, 11:49 AM   #3
AndrewT is online now AndrewT  Scotland
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just guessing but could an electrolytic be leaking badly when it is cold or freshly charging?

When the electrolytic is up to charge and the insulator reformed, the leakage falls to near zero and the pot behaves itself???
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regards Andrew T.
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Old 2nd October 2008, 02:09 PM   #4
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Thanks for your replies.

Quote:
Originally posted by Richard C
I suspect the noise must originate from the volume pot if it only happens when the pot is turned.
I agree although I'm not sure if it's because the pot is more scratchy than it should be and somehow as a cap charges up in the volume circuit it is more apparent or if it's something else. I guess it must be worth swapping out the pot anyway given that it wouldn't cost a fortune to do so.

Quote:
Is the noise level constant regardless of whereabouts the pot position is when it's moved?
Not sure, I will have to check this later.


Quote:
Originally posted by AndrewT
just guessing but could an electrolytic be leaking badly when it is cold or freshly charging?
This is what I was thinking, but I'm, beginning to think that a pot change is the first thing to do. If it's still a problem then I'll look for an if'y cap.

Thanks again chaps.
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