AW: http:/

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Mon Nov 27 21:26:00 CET 1995


>I'm new to this site, but I've been building up a DIY modular
>around mostly Elektor Formant stuff (I managed to find some
>726's after about 3 months of trying.

Congrats! (what did You pay, btw.?)

And welcome to the list!

> I was going through
>your archive, and see that someone is/was planning to build a
>whole bunch of VCO's just to have the stacked sawtooth
>effect. It isn't neccessary as one of the Digisound kits from
>the eighties (Published in ETi) was a unit that from one
>sawtooth in gave six extra sawtooth out all mixed into a
>single output. It constantly phase-shifts all six extra
>waveforms in order to create the effect of sixfractionally
>detuned oscillators. The design could easily be modified to
>provide only four extra waves, or you could build multiple
>modules for more. There are no hard to find bits, it's all
>normal op-amps etc. I haven't built mine yet (I know someone
>who has), as it'll need some mod with a pre-amp to work with
>my Formant stuff.

I thougt about this one myself.
But I haven't built it so far, nor heard it.
Anyway, some things to consider:
(1) Do You really want exactly the same beat rate between
the different saw waves over the whole keyboard range?
(2) The circuit for the phase shifting plus LFOs isn't that
small either. I wonder if very simple but good VCOs in the
kind of Oberheim SEM's would be so much more effort;
maybe we could use a single expo converter for the
whole bank of VCO's?
Think about it: a single CA3046 array plus a single tempco
resistor plus some cheap transistors would make the
heart of a 4-VCO-module. Fine tuning would have to be done
in the linear section, then; maybe in slightly changing the
schmitt trigger thresholds ...
Or build a 3-VCO-module und have a free transistor for
a heater in a thermostat circuit.
And omitting everything You need for generating waveforms
other than saw will make the circuit *very* small. I really
doubt it would be so much more than the phase shifter
solution.

JH.





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