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Old 26th October 2008, 03:37 PM   #1
Puffin is offline Puffin  United Kingdom
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Default Regulated PS for LM3875

I have put together the regulated PS by Carlos Filipe, using the LM338's. For some reason I have a 5 volt mismatch betwen
+ & -, but I am also getting an lot of DC on power-up. Any ideas anyone?
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Old 27th October 2008, 07:15 AM   #2
Nuuk is offline Nuuk  United Kingdom
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Usual comment.
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Old 27th October 2008, 07:22 AM   #3
Luke is offline Luke  New Zealand
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is dc output on both channels? If so disconnect power rails from the faulty channel and see if power rails are correct. If not disconnect both amps and see what happens. You need to isolate your problem first.
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Old 27th October 2008, 07:38 AM   #4
Puffin is offline Puffin  United Kingdom
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Quote:
Originally posted by Nuuk
Usual comment.
Yea, operator error. I have stripped the board and am starting again. Still can't understand why I would get high DC.
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Old 27th October 2008, 08:38 AM   #5
Nuuk is offline Nuuk  United Kingdom
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Well if you showed some pictures, and the circuit you used, we may be able to offer some help.

Incorrect voltage with that circuit is down to either getting the resistor values wrong, or having a short somewhere. That's why a picture would help us to help you!
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Old 27th October 2008, 06:27 PM   #6
Puffin is offline Puffin  United Kingdom
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Sorry a bit late for pics!

I asumed I was being justifiably chastised and went back to the drawing board.

Nick, it was the PS on your site that I attempted.
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Old 27th October 2008, 06:41 PM   #7
Nuuk is offline Nuuk  United Kingdom
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That's a fairly standard LM3** regulator circuit that Carlos optimised for use in the GC. It is easy to make a mistake with the circuit, I often do!

When you try again, get the voltage outputs correct before connecting to the amp section.
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Old 27th October 2008, 06:43 PM   #8
Puffin is offline Puffin  United Kingdom
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Wise words mate
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Old 27th October 2008, 09:52 PM   #9
Zigis is offline Zigis  Latvia
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Lot of DC on amp's output is because large difference between power rails.
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Old 28th October 2008, 08:34 PM   #10
Puffin is offline Puffin  United Kingdom
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Re-made one board. Very slight (0.8v) mis-match between rails, but no DC on turn-on, but a delayed pop/muted thump.

This time I have gone for Nuuk's version of the Filipe PS. I note that CF uses a resistor before the caps, but that is omitted in the Nuuk simpler version. Could this account for the delayed thump?
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