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RE: 6800uf across op amp PS pins?

Posted by erik_sq (A) on January 6, 2017 at 09:10:21

In Reply to: 6800uf across op amp PS pins? posted by Tweaker456 on January 3, 2017 at 08:34:32:

Is it possible you misread, and they suggested 6.8uF?

That makes the rest of your statement more normal.

Typically filter caps go down as they get closer to the destination.

An example for line-level audio (not speaker) would be 10,000uF at the power supply, then 10uF to 20uF before a regulator, 4.7uF after, and then 0.1uF right at the pins.

There's no hard/fast rule but this is all chosen to minimize high current and long runs. The larger the caps, the larger the charging current at turn on, and the bigger the voltage drop, so you'd like to have as big and fat a trace (if not copper/aluminum bus bar) near the power supply, and then decrease. If you put the PS caps at the op amp, or distant regulator, then the charging current would have to travel the distance from the transformer and bridge to there, causing a voltage drop proportional to the current.

Large caps also tend to be more inductive, so less able to filter high frequency noise.

By using a more staggered approach you get the best mix.

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