There is nothing particularly special about the design, it is simply
one of the standard state-variable configurations, albeit using the
inherent integrator action of a (compensated) op amp - it is to be
found in at least one of the filter books that I have. The only
real 'novelty' aspect in the Polivoks appears to be the use
of 'programmable' op amps to provide a variable cut-off frequency. It
should be relatively simple to add another op amp in order to make
the high-pass output available, and the method of setting the current
which 'programs' the op amps could possibly be improved, as the
transistor-resistor set-up is dealing with some pretty small currents
(nano-amps), and I dare say is very sensistive to differences in
individual components, perhaps making initial set-up tricky (but this
is pure conjecture, I've not tried actually breadboarding the circuit
to find out).

Tim

--- In Doepfer_a100@yahoogroups.com , <hardware@...> wrote:
>
> We designed a Polivoks filter about one year ago but we stopped the
project
> as Shawn Cleary of Analogue Haven informed us that such a filter is
under
> development by the Polivoks inventor Vladimir Kuzmin. It should be
available
> soon from Analogue Haven.
>
> Best wishes
> Dieter Doepfer
>
>
> > -----Ursprüngliche Nachricht-----
> > Von: Doepfer_a100@yahoogroups.com
> > [mailto: Doepfer_a100@yahoogroups.com ]Im Auftrag von mss_panzer
> > Gesendet: Samstag, 2. Juni 2007 22:27
> > An: Doepfer_a100@yahoogroups.com
> > Betreff: 1 Filter Suggestion
> >
> >
> > So when might we be able to see a Polivoks VCF Perhaps based on
the A-
> > 124 design, with a HP/LP mix potentiometer and a solo BP pot
> >
> > Anybody have any thoughts on this
>