[sdiy] question about a Mankato filter

[David G. Dixon]

That last message came out a bit more critical than I intended.  I know
several people with Mankato filters, and everybody really likes them.
Indeed, my whole reason for doing all of this in the first place was to come
up with my own Mankato "clone" without the benefit of knowing what was in
the original circuit.  In any case, having filter outputs at increasing
levels isn't really that big of a deal, since output levels tend to decrease
across a cascaded-stage filter anyway, when the filter is actually
filtering.  In this way, having a bit of gain across the filter might even
be a good thing.

I'm just being anal.  Mankato filters rock!


> > I didn't see a response to this yet.  I used a 1 KHz square wave and
> > adjusted the output (input to Mankato) to 10.0 V pk-pk.
> >
> > Input:   10.0V pk-pk
> >    6 dB:   5.0V pk-pk
> > 12 dB:   6.9V pk-pk
> > 18 dB:   9.9V pk-pk
> > 24 dB: 13.7V pk-pk
> >
> > Yes, your assumptions are correct.
> 
> Thanks, David.  David Ingebretsen also did the experiment, and replied to
> me
> offline.  I guess I should have mentioned it before, but it doesn't hurt
> to
> have two confirmatory responses.
> 
> Obviously, I'm not too enamored with the design of this filter.  The
> Mankato
> seems to be optimized for use as a quadrature oscillator, but the filter
> outputs shouldn't be giving these disparate levels.  This is the result of
> using dividers and inverters at various gain levels to equalize the sine
> waves during self-oscillation.  Distributing the resonance gain across the
> four stages overcomes this problem, but does require another quad VCA, and
> hence, increases the cost of the filter.  I guess it's a tradeoff.
> Personally, I'd rather pay the extra $3.50 or whatever to have a unit
> which
> is optimized as both a filter and a quadrature oscillator.
> 
> BTW, I really like your scope graphic.  What are you using?
> 
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