[sdiy] Feedback in filters [was: Re: From a commercialstandpoint...]

[Gordonjcp]

On Wed, May 04, 2016 at 10:37:06AM +0100, Richie Burnett wrote:
> Yes, you can make some filters self-oscillate by feeding one of
> their outputs back to the input with phase-inversion if necessary.
> But it is not a sure fire method that works with all filters.  It
> depends on the maths of the filter.  It works for a moog 4 pole
> cascade because there is 180 degrees of phase shift at the cutoff
> frequency, and that's how the resonance is implemented inside the
> filter normally anyway.  Conversely if you feed back the BP output

So, if I made an eight-pole filter would I need to feed the resonance back in phase with the input then?

Let's leave aside how high the positive rail would need to be, for all those diodes :-D

-- 
Gordonjcp MM0YEQ