SV: Re: [sdiy] Nonlinearities in IR3109 filters

[Antti Huovilainen]

On Wed, 2 Aug 2006, Sean Costello wrote:

> Why so difficult to model diode ladder filters? What about your Moog model,

Delay free feedback paths. In Moog ladder the transistors buffer the 
stages from each other pretty well (transistor beta > 100). In diode 
ladder each stage ínteracts with others.

> but with different pole frequencies for each of the 1-pole sections? This
> might be an oversimplification, but it would display the key behavior (much
> higher feedback gain needed to achieve self-oscillation) in a non-linear

Yes, you could probably fake it by just adjusting the stage capacitors. 
The need for higher feedback gain for self-oscillation comes from the RC 
model. Phase shift reaches 180 later than with Moog.

Antti

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