[sdiy] poor man's alternative to a CS-80?

[Antti Huovilainen]

On Thu, 20 Oct 2005, JH. wrote:

> In no way would I claim that this covers the actual filter in all aspects.
> It does not cover any nonlinearities, for instance. Maybe the actual circuit
> is quite linear (what I would guess - but it's just a guess), then it should

I would assume it is linear or almost linear. I did some simulations of 
SVF using non-linearized OTAs and as soon the nonlinearities became 
significant, the filter went unstable. It is easy to see why:
Q is inversely proportional to feedback and nonlinearities limit feedback 
for high signal levels -> Q increases with signal level, which is the 
exact opposite of Moog derivatives (moog, ssm, cem etc). The fact that 
CS-80 filter deliberately avoids self-oscillation also points to this 
direction.

Also all the SVF circuits I've personally seen have used linearized 
multipliers (JFET or OTA).

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova