SV: Re: [sdiy] Nonlinearities in IR3109 filters

[karl dalen]

--- Sean Costello <seancostello2003 at comcast.net> skrev:

> 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. 

You assumed wrongly. Besides are you saying that digital filters
implementations dont simulate the use of diodes in fedback paths? ..Ugh!

>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.

No filter has higher reso levels then the other per se, wheter hypotetical
or not *any* level can be adjusted, no matter if its a SSM2040 or a ladder
or a SVF. Original moog ladder has an inbuilt defect (design error) i dont know
if that counts as a parameter to judge from regarding the resonance levels.
it shure declines if freq decreases. 

For instance many folks says (2pole SVF type ) SEM filter cant resonate
in sinus, ofcourse it can. Besides is the SSM2040 really an OTA filter?
I tought people here had dissected that filter as a laying ladder?! 

KD

> 
> 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
> > >
> > >
> >
> 
>