yet another(different) pearl voltage problem - diyAudio
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Old 30th March 2005, 10:22 AM   #1
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Join Date: Jun 2004
Location: Montreal
Default yet another(different) pearl voltage problem

Hello,

First of all I want to thank everyone for every previous answers on the pearl. A lot of those helped me.

I'm nearly finished with my pearl. One channel is ok, tested, and it sounds great. I have a problem with the other channel. Every voltage before Q1(IRF9610), is very near the voltage of fig. 5(http://www.passdiy.com/images/projects/pearlfig5.gif) and almost exacly like the working channel.

After Q1(That's before r8) I only have 9v(instead of 29v). I was sure Q1 was the problem so I replaced it. I still have the exact same voltage!

I can't see any difference in grounding. I've got no clue here, please help!

Thanks.
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Old 30th March 2005, 06:08 PM   #2
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Join Date: Dec 2001
Location: Philadelphia
You get to learn something about circuit design!

You've got a little differential amplifier there. The input is the reference voltage set up by D1 (and the current through it) and applied to the base of Q2. 8.95 volts.

The output voltage is supposed to be 29V. A sample of that is taken by the voltage divider consisting of R10 & R11 and applied to the base of Q12 as the feedback to this amplifier. It should be the same to satisfy the requirements of the circuit. That is... 29V x R11/(R10+R11) = 9.0V.
For all intents and purposes, the same as the reference.

So, check the reference voltage, check the feedback voltage, check to make sure the feedback voltage divider is working right, etc.

If your R10 and R11 are correct, then you must have only about 2.8 volts at the base of Q12, right? Why is it satisfied if that is the case? Is your reference correct?

Give it a go.
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Old 31st March 2005, 12:44 PM   #3
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Join Date: Jun 2004
Location: Montreal
Thank you for the answer Vince!

The problem is solved! I was so sure the problem was at the output of Q1 that I didn't realise the link with R10/R11. There was a bad connection there.

It's now up and running, and god it sounds great!

Thanks again everyone.
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Old 1st April 2005, 03:56 AM   #4
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Join Date: Dec 2001
Location: Philadelphia
Glad I could help. That's one of the few circuits I fully understand. Despite that, I didn't really know what was wrong, but I knew it was there somewhere. I was assuming that you had a PCB, and now realize that you probably don't. I think we learn much more without them!
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