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Old 30th January 2013, 05:48 AM   #1
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Default Purpose of power supply filter caps on amps?

Assuming for have a perfect power supply powering your amplifier why are multiple caps this large seen in schematics such as this? If this was to tame high frequency transients, wouldn't the caps be on the order of 0.1uf to 10uf?
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Old 30th January 2013, 06:07 AM   #2
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You have a few premises that need to be modified. The perfect power supply has yet to be built. It's also more important to first deal with the 50/60Hz or 100/120Hz frequency after rectification. Have a look at this pdf, especially noting the waveforms in figures 1, 2, and 5.
Taming those HF transients is probably most commonly done downstream right at the power connections of sensitive components.
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Old 30th January 2013, 06:10 AM   #3
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They are for smoothing .... A perfect power supply would not need smoothing
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Old 30th January 2013, 06:48 AM   #4
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Sorry I don't think you guys understand my question and I forgot to post the schematic im referring to in my original post. I am talking about schematics such as these:

http://sound.westhost.com/articles/class-g-f9.gif

And this is assuming the power supply for his schematic already has large caps after the rectifier to provide low ripple.
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Old 30th January 2013, 06:56 AM   #5
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Thats a very specific circuit with multiple rails. Do you mean why fit 100uf caps when the 70 and 35 volt rails are "perfect" ?

If so its because the rails become "imperfect" after travelling down a few inches of wire and PCB. The 100 uf is a good compromise value to maintain a low impedance.
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Old 30th January 2013, 07:10 AM   #6
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It's sort of like my comment about taming HF at the component. Those rail caps will supply some bypass/reservoir close to the main circuit. This is sometimes done even with battery-powered circuits.

Sorry about the confusion. I figured the "such as this" was some circuit you saw in the forums.
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