[sdiy] SVF High Pass Mode not Cutting Off

[David G Dixon]

> > Thanks for the help, I tried lower integrator cap values (220pF 
> > instead of 470pF) but without any change. I have plenty of 
> Freq range. 
> > on the pot. A sawtooth waveform is "squashed" to a flat 
> line as Freq 
> > is turned up but a very sharp spike is left at the trailing edge of 
> > the saw no matter what the VCO freq is. Any thoughts?
> 
> Isn't that supposed to happen?

I don't think so, at least not to an annoying extent.  As I said before, I'm
pretty sure that the problem here is imperfect cancellation of the LP and
input signals at high cutoff.  The cure is definitely to tighten up the
resistors on the input summer, and even perhaps to make one a tad smaller
than the other and add a trimmer in series which can adjusted to perfect
cancellation.  The problem is that even a few mV of bleedthrough will be
quite audible.  I had this problem with the Korgo, and we fixed it (mostly)
with 0.1% resistors.