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Old 16th July 2007, 05:42 AM   #1
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Default Distortion? or Clipping?

Hello Everyone!

I have a problem with my ESP P3A amp. It works beautifully up to a certain high volume level. When I turn the volume loud (not really loud), on certain songs where there's strong bass, I hear a slight fuzz *tststs* sound. This only happens on one of the two channels. I'm using the same components on both channels. Another thing is, when I turn the good channel off, the channel that fuzzes does not fuzz anymore. Does this point to a problem in the power supply? I don't think it's clipping because one channel does not ever exhibit this problem. Any suggestions would be appreciated?

Thanks
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Old 16th July 2007, 05:46 AM   #2
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sounds like something with grounding topology. Try experimenting with it and avoid any forms of loops.
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Old 16th July 2007, 05:59 AM   #3
jnb is offline jnb  Australia
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Could it possibly be that one of your transistors has gone into secondary breakdown and needs replacement?
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Old 16th July 2007, 06:17 AM   #4
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Secondary breakdown? I've replaced the power transistors already when trying to fix this issue. So are the driver or first stage BJT's susceptible to secondary breakdown as well?

I'm using 10,000uF on the rails. I was thinking about dropping this to 4,700uF to see if it would help. Does it make sense to try this?

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Old 16th July 2007, 07:15 AM   #5
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Lovering the rail cap value vill not help you in this matter....

If the buzz is in the range of 60 to 120 Hz I will support darkfenriz in the ground loop problem.....

Otherwise I would check all solderings one time more
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Old 16th July 2007, 09:05 AM   #6
jnb is offline jnb  Australia
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It is conceivable. BTW, I've encountered this fuzz problem with op-amps. The fuzz seemed level dependent and was a little more like modulated white noise than hum.
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Old 16th July 2007, 10:00 AM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
could this be instability in one channel causing oscillation?
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Old 16th July 2007, 08:31 PM   #8
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I'm pretty sure it's not a ground loop hum. It's a white noise sound like jnb describes. I am more inclined to think it is a transistor, but wonder why it only occurs when both channels are playing. The noise does not occur if only the one channel is playing. Could it still be the transistor?

Thanks
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Old 16th July 2007, 08:57 PM   #9
anatech is offline anatech  Canada
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Hi blap0220,
Quote:
I am more inclined to think it is a transistor,
From ...
Quote:
Could it possibly be that one of your transistors has gone into secondary breakdown and needs replacement?
No.
Once a transistor has gone into secondary breakdown, it has become a piece of wire that only looks like a transistor. Your problem is not a transistor.

I would support some of the other posters here like darkfenriz who is on the right track with ........
Quote:
sounds like something with grounding topology. Try experimenting with it and avoid any forms of loops.
ACD with ...
Quote:
Otherwise I would check all solderings one time more
AndrewT with ...
Quote:
could this be instability in one channel causing oscillation?
who I completely agree with. The instability could be caused by a number of things, so recheck all you work and solder joints carefully.

All these members are pointing along the same path, even though it may not appear that way.

-Chris
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Old 17th July 2007, 05:56 AM   #10
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Well. I'm reluctant to believe it's a solder issue because I've touched every joint over. Doubt it's because of ground loop, because there is no hum. And the other channel works just fine. My wiring is pretty good as far as the layout. I am most interested in JNB's suggestion because he says that he has encountered this buzz before. Can a transistor be someone degraded but still functional?
THanks
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