[sdiy] Pole Mixing

Neil Johnson neil.johnson71 at gmail.com
Mon Apr 12 12:46:45 CEST 2021


Hi Tom,

> It switches between 33n and 100pF. Page 26 in the Xpander service manual, and also in the schematics at the end.

Ah dammit yes I see now - ".033" = 33nF.  Not 0.033nF.

Even so, when "off" that still leaves a high-frequency pole in the
signal path, albeit 330x up in frequency.  I guess the small phase
shift it causes is not too much of an issue, but I wonder what subtle
effect it has in the audio path?  Also.. why bother with the 100p
capacitor at all?  Maybe the VCF is unstable with very small (a few
pF) capacitance, and they found 100pF was enough to keep it stable yet
keep the pole far enough away from the audio region?

Neil
(hates schematics where the unit is not explicitly written)


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