[sdiy] Filter Not so strangeness

[harrybissell]

The PAiA LPF is not even a Voltage Controller "cutoff" filter... it is a
Voltage Controlled "attenuation" filter... like a tone control.
It cannot be made resonant easily (in fact I don't think it can be made
resonant at all, since cutoff never changes).

I agree with your decision to abandon the Sallen Key design (flamesuit on)
I don't really prefer that one anyway.

I'd suggest you look for some other designs.  Maybe a visit to EFM (Electronics
for Music)
is in order... there are some simple filter designs there. I'd suggest buying a
pcb if they
are available. Another good choice would be Ken Stone, who has a Steiner-Parker
Synthracon
clone (and a cheap board)

As an original PAiA 2720 user... the weakest module was the LPF (probably
followed by the BPF).
It is a good choice for a dead simple filter, but it will be the first one you
abandon (imho)]

H^) harry

Pat Kammerer wrote:

> Well,
>
> I ditched the sallen key filter I was working on, mainly because I had made
> just couple more mistake than I felt like fixing.  : )  So I've been looking
> around at different designs.
>
> I've thrown together a PAIA 2720 VCLF  (I know...), and I love the sound,
> much stronger and less noisy than the other. It also seems to like single
> polarity supply.
>
> http://www.muzique.com/schem/2720-3l.gif
>
> My question now is to anyone who may have built this into a module or
> whatever;
>
> I've read that to control resonance in this circuit you need a pot in series
> with the bypass capacitor that is across the emitter resistor.  I don't see
> this cap in the schematic unless I'm misunderstanding the word across  (?!)
> Or is the bypass cap the one at the supply input (100uf)?  I would like this
> option as it would make the sound much more versatile.  Theoretically,
> instead of voltage control for cutoff I could use a varying resistance from
> the two .05p caps to ground right, since the voltage creates a varying
> restance using the 1n914's?
>
> Fun simple circuit though.
>
> Thanks for your help