Anushri VCF op-amp question

Discontinued DIY products Anushri
#1

In the Anushri VCF circuit, a full rail-to-rail op amp (like MCP33204P) gives less distortion and a cleaner sinewave at self-oscillation than a standard TL084. The drawback is a loud pop when VCF attack is zero. I’ve tried AC coupling the gain cells of the 2164D and it doesn’t help, so I don’t think it’s a DC offset issue. Heavily filtering the DAC output certainly helps but there’s still a whump. Just something about the filter design that does not like swinging fully to the rails.

I appreciate your filter design as it gives good results for few parts. Just wondering if there’s a simple fix to get a little better oscillation from it.

#2

> gives less distortion and a cleaner sinewave at self-oscillation than a standard TL084

Or you can change the value of the Zeners?

Have you looked at which property of the waveform can explain the thump? Is that a strong discontinuity at 0?

Also, attacking the VCA with larger signals will cause distortion…

#3

It turns out I am over-driving the VCF audio input. I threw in a quick 1:1 voltage divider and sure enough, not only did that clean up the distortion but now it self-oscillates smoothly across the audible spectrum.

Thanks for your help!