Need a 12.6 VDC power supply schematic - diyAudio
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Old 21st May 2011, 02:32 PM   #1
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Default Need a 12.6 VDC power supply schematic

Hello everyone. I recently finished my hybrid 12AU7/IRF510 headphone amp, and it sounds wonderful The problem is, there's a bit of hum every once in a while, and I think it's the power supply that's the problem. Here's a schematic for it:
Click the image to open in full size.

Now I've tried building that schematic 2 times, but it outputs about 15 VDC I'm looking for a regulator schematic that inputs about 15-20 VDC and outputs 12.6 VDC. If anyone has any suggestions I would be really thankful
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Old 21st May 2011, 02:40 PM   #2
TG is offline TG  Ukraine
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Changing RR1 from 120 to 270 Ohm will be quite enough.
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Old 21st May 2011, 02:50 PM   #3
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Quote:
Originally Posted by TG View Post
Changing RR1 from 120 to 270 Ohm will be quite enough.
Thanks, I'll do that and report back here
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Old 28th May 2011, 05:05 PM   #4
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I changed RR1 but it still outputs about 15 VDC. I don't think it's the LM317, since I tried 3 different ones. Can anyone give me another schematic for a 12.6 VDC regulator ?
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Old 28th May 2011, 05:17 PM   #5
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Can anyone please help me ? I need this quite soon...
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Old 28th May 2011, 05:34 PM   #6
TG is offline TG  Ukraine
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What voltage is at the LM317's IN terminal?
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Old 28th May 2011, 06:00 PM   #7
tomchr is offline tomchr  United States
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The schematic is fine. The issue is with the resistor values. Try these values:

RR1 = 220 ohm
RR2 = 1500 ohm
RR3 (pot) = 1000 ohm

The output voltage is Vout = 1.25*(1+(RR2+RR3)/RR1) in your case. Hence, above values should yield an adjustment range of 9.8 ~ 15.5 V.

~Tom
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Old 28th May 2011, 06:11 PM   #8
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I think your Vin is too low, the LM317 needs about 3V to operate. As an experiment try increasing Vin, try about 18VDC that should prove the point.

Last edited by Andy5112405; 28th May 2011 at 06:14 PM.
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Old 28th May 2011, 06:27 PM   #9
TG is offline TG  Ukraine
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Initial resistor values (with RR1 = 270 Ohm) are fine too.
I have a suspicion that DR3 and/or DR2 are mistakenly reversed.

With too low Vin LM317 should output about Vin-1.2..2V depending on load, so I believe this is not the case.
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Old 28th May 2011, 08:35 PM   #10
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It seems the trim potentiometer wasn't properly working. Well, actually, not one, but THREE of them ! I am that unlucky. I bought a proper trim potentiometer so now it works.
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