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Old 12th June 2003, 06:58 AM   #1
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Default P3A questions, problems

Hi gang. I am building ESP's P3A and have a few questions. Here goes.

1. After finishing construction and testing both channels, both were working fine with some low level hum. See #2 below. Very good performance otherwise. I was almost satisfied, and (you know what happens next) I droped the input RCA connector into the output terminal and !BZZZT!, one dead left channel. The MJL2113/4 outputs and BD139/40 drivers are very dead. Should I replace all transistors in the VAS and diff pair just to be on the safe side? How about other components that look and check ok?

2. I have cut Rod's boards in half. D. Self and R. Slone have recommended running a separate ground for the rail decoupling capacitors. ESP boards do not appear to be built that way. Am I missing something? How important is a separate return for these caps?

3. The 100pF dominant pole compensation caps I am currently using are of the ceramic type. Obviously the input cap should be of high quality(polypropylene?). What has been everyone's experience with different types of Miller caps in this amp?

Thanks in advance,

Big gain
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Old 12th June 2003, 09:23 AM   #2
trwh is offline trwh  United Kingdom
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Big gain,

Did you check here:


You will need your username and password, as supplied with your PCB, to read it.

See ya,
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Old 12th June 2003, 04:35 PM   #3
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Hi there!

Sorry bout your amp, you are not alone when it comes to burning transistors, welcome to the club!

I have tried those expensive capacitors and those cheap ones and I really can't tell the difference. Still, it's a good thing to know that my amp has the best parts as long as I can afford them. But if you have the ceramic types then maybe you can listen a little bit before you change them to propylene types.

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Old 12th June 2003, 07:53 PM   #4
sam9 is offline sam9  United States
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I think what Self and Slone really mean is a separate ground for the bypass cap (usually 220-330uF) you find on the the NFB return. It means the same thing when said either way, but to me the latter is clearer. Slone's designs didn't have this in earlier versions ans sounded OK. I suspect it is a precautionary measure - doesn't improve something that in functioning OK but precludes certain problems that occassionaly arrise.
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