Tweakers' Asylum

Posted by Al Sekela (A) on February 26, 2009 at 14:34:33

In Reply to: RE: Final speaker cable filter questions posted by JLSmith on February 26, 2009 at 10:00:17

I originally posted this tweak with silver-mica caps based on recommendations from another inmate. I compared silver-mica with various film types and preferred the silver-mica above all but a few polystyrene. However, when I made the comparisons, I did not try metallized paper (Wima MP3) suppression caps. I still have the silver-mica caps in my system, but I've used Wima caps in AC power filters with good results. If I were to revisit this tweak, I would try Wima MP3 caps and compare them with silver-mica. A friend of mine has done this and prefers metallized paper to silver-mica.

Note: silver-mica are NOT suitable or safe for AC power filters, no matter what voltage rating!!!

The cap voltage rating should be enough to avoid breaking the caps with peaks from your power amp. A rating of 100 volts would be adequate, but don't go lower. The resistor power rating is unimportant, as the resistor only sees high frequency noise. PRP half-watt resistors are about the best for sonic reasons.

The original Walker Audio High Definition Links design is a single 0.01 microfarad capacitor (10,000 pF) in series with a single 10-ohm resistor. At the time I made my comparisons, I could get 10,000 pF silver-mica caps cheaply from a local electronics house with a surplus room, and from Hosfelt. Once I posted my results, the 10,000 pF caps from both sources quickly disappeared. I believe new ones go for more than $9 each, so putting three 3000 (or so) pF caps in parallel is a good alternative. These will have a higher self-resonance frequency, and putting them in parallel may make the resonance more complex, but the main effect will still be the same.

For the purposes of making a wider bandwidth filter, use the same resistor value in all stages. However, the smaller caps will be effective at higher frequencies, where cable resonances are more prominent. Capacitor resonances are also an issue. This means higher resistance values may work better with the smaller caps. This is something you would have to experiment with, as I've not explored this aspect with speaker cable filters.