[sdiy] CEM3372 passband gain trick?

David G Dixon dixon at mail.ubc.ca
Sun Aug 12 18:12:59 CEST 2012

> Another way to do it which is straightforward if you have 
> implemented VC-resonance through a gain cell controlling the 
> amount of 4th stage output fed back into the input: feed the 
> filter input signal into this gain cell. This is equivalent 
> to increasingly adding an extra amount of the input signal at 
> the input of the filter when resonance is increased. The 
> transfer function would be:
> (1 + 4k) / (4k + (1 + s) ^ 4)
> Where k is the resonance control and goes from 0 to 1.
> Seen for example in the JP-8:
> http://fa.utfs.org/diy/roland_filters/JP8.jpg (25A is the OTA 
> responsible for CV-resonance).

Doesn't the MOTM 440 do more or less the same thing?

The advantage of doing it my (much more complicated) way is that all the
sine waves come out at the same amplitude at self-oscillation.

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