Regulated PS for LM3875

Puffin · 26th October 2008, 03:37 PM

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?

Nuuk · 27th October 2008, 07:15 AM

Usual comment.

Luke · 27th October 2008, 07:22 AM

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.

Puffin · 27th October 2008, 07:38 AM

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.

Nuuk · 27th October 2008, 08:38 AM

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!

Puffin · 27th October 2008, 06:27 PM

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.

Nuuk · 27th October 2008, 06:41 PM

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.

Puffin · 27th October 2008, 06:43 PM

Wise words mate

Zigis · 27th October 2008, 09:52 PM

Lot of DC on amp's output is because large difference between power rails.

Puffin · 28th October 2008, 08:34 PM

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?

26th October 2008, 03:37 PM	#1
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	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?

27th October 2008, 07:15 AM	#2
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	Usual comment. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

27th October 2008, 08:38 AM	#5
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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! __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

27th October 2008, 06:41 PM	#7
Nuuk diyAudio Member Join Date: Feb 2003 Location: Somerset, SW England	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. __________________ The truth need not be veiled, for it veils itself from the eyes of the ignorant.

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27th October 2008, 07:22 AM	#3
Luke diyAudio Member Join Date: Sep 2001 Location: Wellington NZ	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.

27th October 2008, 06:27 PM	#6
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	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.

27th October 2008, 06:43 PM	#8
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	Wise words mate

27th October 2008, 09:52 PM	#9
Zigis diyAudio Member Join Date: May 2005 Location: Riga, Latvia	Lot of DC on amp's output is because large difference between power rails.

28th October 2008, 08:34 PM	#10
Puffin diyAudio Member Join Date: Feb 2006 Location: U.K	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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