P3A questions, problems

Big gain · 12th June 2003, 06:58 AM

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

trwh · 12th June 2003, 09:23 AM

Big gain,

Did you check here:

http://sound.au.com/secure/troubleshooting.htm

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

See ya,
Tim.

JojoD818 · 12th June 2003, 04:35 PM

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.

Cheers!
Jojo

sam9 · 12th June 2003, 07:53 PM

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.

12th June 2003, 06:58 AM	#1
Big gain diyAudio Member Join Date: Apr 2003 Location: Oregon	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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12th June 2003, 09:23 AM	#2
trwh diyAudio Member Join Date: Apr 2002 Location: UK	Big gain, Did you check here: http://sound.au.com/secure/troubleshooting.htm You will need your username and password, as supplied with your PCB, to read it. See ya, Tim.

12th June 2003, 04:35 PM	#3
JojoD818 diyAudio Moderator Join Date: Mar 2003 Location: searching...	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. Cheers! Jojo

12th June 2003, 07:53 PM	#4
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	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.