6581 filter capacitor values

[annuvin]

on the schematic the filter capacitors C3 and C4 are labeled as being 1nF however the proper value for a 6581 would be 470pF (8580 is 22nF) the value can be experimented with however, with the datasheet calling for 2200pF.

[roybaer]

To the best of my knowledge, the 1nF (or 1000pF) filter capacitors are true to the original, i.e. they are reportedly what Innovation used.
Ostensibly that was the recommended value in some version of the data sheet.
Incidentally, the recommended value for a MOS 8580 appears to be 6800pF, regardless of what the C64 uses.
Source: https://nerdlypleasures.blogspot.com/2014/01/sid-and-dos-unlikely-but-true-bedfellows.html, among others.

I have to admit, though, that the schematic does not actually mention any filter capacitor values for the MOS 8580 configuration.

Side note: Keep in mind that the SID on this card is clocked at 1/16 of the ISA bus oscillator signal and therefore runs at a ~10% lower frequency than the SID in a C64. I.e. it is not going to sound like a C64 either way.