PS Cap to V- larger than the Cap to V+ - diyAudio
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Old 31st May 2004, 08:22 PM   #1
GregGC is offline GregGC  Canada
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Default PS Cap to V- larger than the Cap to V+

I was looking at the PSRR of LM3875 and I thought that it would make a perfect sense to use 2 ore 3 1000uF caps in parallel to the V- and only one 1000uF cap for V+ of the PS. This way I'd get better LF and HF filtering and thus compensate for the PSRR differences. Should have a positive effect (at least in theory).

Has anyone tried that?

/Greg
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Old 31st May 2004, 08:28 PM   #2
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Greg, when powering off the amp, the negative rail will have voltage a little longer.
And that may put huge DC on the ouputs.
Have you thought about this?
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Old 31st May 2004, 08:39 PM   #3
GregGC is offline GregGC  Canada
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Carlos,

No, I didn't think about that. Very good point. Though, if it really makes things better and it's worth the trouble you may have a relay that disconnects the speakers as soon as you power-off the amp.

Considering the above problem, it makes more sense to just increase both V- and V+ caps at the same time.

/Greg
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Old 31st May 2004, 10:16 PM   #4
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Greg, on a sonic point of view, between 1,000 and 1,500uf is the ideal.
I made extensive tests.
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Old 1st June 2004, 01:50 PM   #5
GregGC is offline GregGC  Canada
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Carlos,

Thanks for the feedback.

/Greg
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