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Some starting points...

Posted by Al Sekela (A) on October 24, 2009 at 15:04:09

In Reply to: RE: I'm not sure where the DC resistance guidelines came from. posted by andy2667 on October 23, 2009 at 16:25:37:

The design is proprietary and involves others, so I can't post it. However, you can easily do some experiments and come up with a design you like without spending a lot for parts or shipping.

I use a set of different capacitor values, with all the R-C strings in parallel. Each cap has a self-resonance frequency above which it acts like an inductor. Using a set gives broader frequency coverage for damping the noise.

Use only suppression capacitors that have AC voltage ratings. These come rated as "X" for line-to-neutral and "Y" for line-to-ground service. The different ratings reflect different test conditions and approvals by safety agencies. "X" caps can fail to short or open under the expectation that the circuit protection device (fuse or breaker) will operate to kill the power in the event of a short. "Y" caps should only fail to open-circuit, as energizing the safety-earth could cause a lethal condition. It is perfectly proper to use a "Y" cap for line-to-neutral, but not proper to use an "X" cap for line-ground.

Suppression capacitors come with a variety of dielectrics. The only ones I like for use with an audio system are the Wima metallized paper, MP3. Rifa metallized paper are also available, but these use plated steel wire leads, while the Wima are non-magnetic. This seems to matter.

You can use flame-proof resistors or the PRP resistors encased in flame-proof Teflon tubing. The filter should be constructed so that it does not start a fire if one of the capacitors should fail to a short-circuit.

Use a symmetrical construction of -R-C-R- instead of a simple resistor and capacitor in series for each string.

Experiment with higher values of resistance. Each different cap size seems to prefer a different amount of series resistance.

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