P3A strange problem (thumb when applying input signal) - diyAudio
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Old 25th February 2010, 04:51 PM   #1
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Default P3A strange problem (thumb when applying input signal)

Hello! This is may first post in diyaudio.com. Hope you will understand my english.
I built esp P3A power amplifier about month ago and I was very satisfied. But one bad day while amp was on, but no input signal applied suddenly I heard "tick" in one speaker and it fried out because that channel gave 30 V DC in output. Other channel was ok and I compared voltages between them and couldnt find any problem. Than I powered it again and funnily enough it was back to normal - no DC , no problems at all . Sounded like before.
Then I noticed one thing about that channel. When I power up/down whole amp there are no turn on/off thumb/tick at all. But when I apply signal to that mentioned channel I get loud "TICK!!". After that it works without any problems - great sound, DC offset about 2mV. But when I take off input, after 5 seconds again - same loud TICK!. Tick again when I apply input and so on.
With other channel there are no problems.
So what could cause that? Never heard of this kind of problems anywhere.
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Old 25th February 2010, 08:09 PM   #2
jaycee is offline jaycee  United Kingdom
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I can only think either a bad solder joint or one of the transistors is bad, but only intermittently.
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Old 25th February 2010, 09:09 PM   #3
mjf is offline mjf  Austria
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hello.
.........perhaps you have built in a wrong part or an elko reverted.......compare the two channels.
greets
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Old 26th February 2010, 07:25 AM   #4
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Thanks for replies.

I found why it thumped when applying/taking of signal. It was my laptop.
I was using vista and there were no problems, but when I installed Ubuntu it started to thump in one channel. In earphones I could hear it too. Im happy its not amps fault.
But it doesnt explains why it fried my speaker. (It was before the ubuntu installation). One thing I found - C3 was soldered wrong way. Does it explains why it worked great about week without any problems, than killed my speaker with 30V DC, and then without any fixing came back to normal?? (
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Old 26th February 2010, 11:49 AM   #5
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check your "mechano" means loose conatcts and especially in power supply area
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