[sdiy] Nonlinearities in IR3109 filters

[Sean Costello]

Hi all:

Scanning through some old posts, and I saw someone discussing a digital
emulation of the SH-101 filter. The discussion pointed out something I have
never seen before: the SH-101 has back-to-back diodes going to ground in the
feedback path of the filter.

Is this the reason that the SH-101 has a fairly nonlinear filter? I have
always thought that the sound of the filter was due to the IR3109 chip, but
I always wondered why my Juno-60 filters (which use the IR3109) sounded weak
next to the SH-101. Do any of the other Roland synths have clipping in the
feedback path of an IR-3109? How about clipping in the feedback path of
filters using other OTAs?

Any observations welcome.

Sean Costello