[sdiy] EN#37 State Variable Filter

[Ian Fritz]

Michael --

That's another great design from list member Terry Michaels, with minor 
modifications by Bernie.  I made some more modifications for myself and 
have used it for years and years.

The notch control changes the position of the notch with respect to the 
peak of the resonance.

The "limit" input prevents saturation as the Q is increased.

I added a bit of feed-forward phase compensation to alleviate Q enhancement 
at high frequency, and I also replaced the single FET buffers by 
zero-offset pairs.

   Ian

At 01:02 PM 4/16/2003, Michael Schulze wrote:
>I am currently doing a pcb layout for the EN#37 State Variable Filter from
>Hutchin's Musical Engineer's Handbook.  I am wondering if any of you have
>built this circuit and if you have any comments about it.
>
>Also a question - on my schematic PC6 feeding the op-amp just before the
>notch output - what does this control do?  Controls the depth of the
>notch???
>
>Also I assume the "Limit" in negatively scales the output amplitude?
>
>Thanks in advance for the wisdom!