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Old 10th June 2008, 12:50 PM   #11
Nuuk is offline Nuuk  United Kingdom
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Hmm... With 30v supplies, one LM3875 sink more than 3.5A, in this case, do you think 317/337 will enough, especially if you take consider my speakers sensivity is just 86dB!
I'm confused Ozgur! Are you using the same supply for the buffer and your amp?

As Andrew says, the ideal solution is to use a lower voltage traffo for your buffer supply. I used an 18v one for mine, followed by two stages of regulation so each stage drops about 5 volts which doesn't stress the regulators, or require heatsinks. Full details
here .
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Old 10th June 2008, 12:58 PM   #12
Dxvideo is offline Dxvideo  Turkey
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I guess, the problem is using the same PSU for buffer stage.. Youre right..
Because a lot of people use that (the first stage of PSU) design for chipamps.. However using LM337 just after LT1083 may cause that problem. So I will remove the 317/337 regulators and test it again...
I hope it will work.
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Old 10th June 2008, 01:05 PM   #13
Nuuk is offline Nuuk  United Kingdom
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For the cost of another small traffo and rectifier bridge etc, I would build a separate supply for your buffer!
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Old 10th June 2008, 01:15 PM   #14
Dxvideo is offline Dxvideo  Turkey
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I have a spare 2x15v toroid trafo... So the cost is not a problem..
I will try it. Do you think my supply will work without LM317/337 pair?
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Old 10th June 2008, 01:22 PM   #15
Nuuk is offline Nuuk  United Kingdom
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Without 317/337? It won't be regulated then. Or do you mean to keep in the 1083's?
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Old 10th June 2008, 01:44 PM   #16
Dxvideo is offline Dxvideo  Turkey
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No meant;
If I remove the LM317/337 will it work at just +/-30v rails..
But its not an issue for now. I removed the 337 and it works fine, +/-30v is ok...
But thats really weird! It would be work with LM337 also! I am confused.. Do you have a explanation?
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Old 10th June 2008, 03:22 PM   #17
Dxvideo is offline Dxvideo  Turkey
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I found the reason of that fault. The LM337 is definately dead!
Now I ve replaced it with a new one (the old one was also new!)
and it works...
I will report about the results under this topic...
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Old 12th June 2008, 07:09 AM   #18
Dxvideo is offline Dxvideo  Turkey
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I've tested one of my amplifier last evening. (With this regulated supply).
I can say only one word: EXCELLENT!
Thanks Pedja, youre a real guru..
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Old 26th June 2008, 05:03 PM   #19
thoronx is offline thoronx  Yugoslavia
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Dxvideo , can you post your pcb of LM3875 Amp with Pedja's buffer, thx.
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Old 26th June 2008, 07:27 PM   #20
BWRX is offline BWRX  United States
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Now build one with the AD797 and see which one you think sounds better instead of letting everyone else decide for you.
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