[sdiy] Nonlinearities in IR3109 filters

[Sean Costello]

I had just assumed that most OTA filters relied upon the nonlinearities in
the OTAs themselves to keep the self oscillation amplitude within reasonable
areas. Antti's analysis of a hypothetical SSM 2040 seems to indicate that an
OTA based cascaded 4-pole with feedback will have higher self-oscillation
amplitude than a Moog ladder, unless some sort of feedback limiting is
included. Very interesting.

Sean Costello

----- Original Message ----- 
From: "karl dalen" <dalenkarl at yahoo.se>
To: "Sean Costello" <seancostello2003 at comcast.net>;
<synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, August 02, 2006 1:00 PM
Subject: SV: [sdiy] Nonlinearities in IR3109 filters


> Well clipping by the means of diodes in the feedback is not a new thing!
> Actually its a neccity otherwhise at high reso evrythings overlads.
> SH09 has that diode to gnd using 3080. SEM to, but more of the classic
> diodes in series with signal.
>
> KD
>
> --- Sean Costello <seancostello2003 at comcast.net> skrev:
>
> > 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
> >
> >
>