PolyModular

[Rene Schmitz]

Hi DIYers,


The main trouble to me is the problem of maintaining tracking, and tuning
on a bunch of VCOs. I think proposed linear keyboard control is too
limiting, i.e. MIDI -> CV convertors usually work with expo VCOs. (I'm such
a poor keyboard player)
Considering the increased circuit complexity, I think autotune using a
"D"PLL would be relatively easy.  Using a uC, PIC or even discrete logic.
The circuit would have do disconnect the tuning pots of the vector-VCOs and
supply a tuning voltage corresponding to the reference frequency.
The PLL would consist of a phase discriminator (the lead/lag edge-triggered
type..) one of the VCOs is put into the loop. The filter of the PLL would
be an up/down counter initialized to 0.5 (i.e. 127 in case of 8-Bit) the
output of the counter would be connected to a register followed by a dac.
(Or a dac and a S&H.) The counter would be incremented on a lagging pulse
and decremented on a leading pulse. The output of the DAC is the correction
voltage for the VCO. No need to copy the circuit n-times just the "memory"
for the error signal has to be copied. Either n-times register and dac or n
S&Hs. I'd certainly opt for the S&Hs. Could be el-cheapo 4051 + caps.
I think this could even be done using discrete logic, but with a micro one
can simply put it into one RAM, and refresh the S&Hs from time to time with
the stored values so that the effects of leakage would be minimal. 

The circuit that I tried to describe could of course find application in an
"ordinary" modular or polysynth.

Finally I think that I'm not going to own a PM any time soon, but I have
the idea of haveing mostly all-VC modules and loads of uncommited VCAs on
my modular.
I think it's somehow wasted if you have 5 VCOs and cannot crossmodulate two
of them, use one as LFO and get a bassline from the next one.

Bye
 René

             ,   : (uzs159 at uni-bonn.de)
|") [" |\ | ["   : (http://www.uni-bonn.de/~uzs159)
|"\ [_ | \| [_   : (http://members.xoom.com/Rene_Schmitz)