More Nonlinear filter feedback

[Sean Costello]

Paul Perry wrote:
> 
> At 03:43 PM 23/07/98 +0200, Scott Gravenhorst wrote:
> >
> >Is nonlinear feedback in a filter viable?
> ....well yes...
> so is nonlinear feedfoward, I suppose....
> the analysis might be hairy though!
> Where it is interesting is when the filter approaches oscillation,
> and limits. Under these circumstances, nonlinearities in the
> feedback path make all the difference.... see the Korg MS20
> resonant filter for an example.

Having no MS20 filter to play with (although I have 2 LM13700's that I
might use to create a rather inaccurate clone), I am curious.  Can you
describe the effect of the diodes in the feedback opamp of the MS-20
filter, from an aesthetic perspective?  Or from an electronic
perspective?  Also, is there any differential amp distortion in the
MS-20 from the inputs of the LM13600's, or are the signal levels too
low?

Thanks,

Sean Costello