[sdiy] IR3109 (OTA-based) filter question

[>>>marjan<<<]

> That's why you need to add another VCO to the Polysix voices.  Get to work,
> Marjan!

:) yep, that'd be one fantastic synth then...
I've considered doing that, but some problems emerge from the specific
p6 construction. VCO core section is pretty simple, together with
it's suboctaves and maybe noise gen. You'd need then 6 OTAs co control
VCO2 levels (at least that, if not at both). Those are linear with
one common multiplexed expo converter (wich uses vactrol among other 
things btw), so if I want separate VCO2 modulation I need to duplicate
this expo, otherwise I'd have just linear detune of VCO core.
Biggest problem is octave switching as octave bits are processed
together
with kbd data in 8049 and then converted to CV (which is 0.5V/oct),
so I can't have separate octave switch for other VCO, unless I buld 
another R2R DAC and extract ROM from 8049 and clone it. Way too much
trouble. Maybe those octave switch just add some high bits to DAC,
which eliminate need of another 8049, but I'd need to investigate more.
My "secret" plan is to get another p6, hack off the kbd and add it as an
expander to original one. Separate set of VCOs, separate set of
envelopes
for VCA, another 3 programable LFOs (of 4 that p6 has), 6 2044 for
another
projects :) and the whole logic cct to momorise all other parameters,
and having some stuff removed it can be used to memorise some new
modulation
parameters etc.


cheers,

marjan