[sdiy] Interesting article on top octave generators.

[Michael E Caloroso]

The Moog Polymoog was a dual VCO rank TOS system using a pair of TOGs but
with an interesting twist: one TOG was offset from the other by a semitone
(per US patent  4,145,943 and 4,228,717).  In other words when you pressed
a key with both ranks engaged, you were hearing one TOG at its nth divider
output plus the other TOG as its n+1th divider output.  The master
oscillators were offset so that n and n+1 divider pairs produced the
(approximate) same pitches.  Because the TOG can't produce equal 12th root
of 2 temperaments at all its dividers, this offset resulted in dissimilar
scaling offsets per semitone with both ranks engaged.  With pitch
modulation, it produced a richer string ensemble chorus effect and deviated
the waveshapes of each rank.  The cent difference of ranks when a key was
depressed was not uniform between keys, the largest being ~3.3 cents.  This
gave the Polymoog an organic sound quality and probably prevented dividers
from syncing up.

Before he joined Moog Music in 1972, Dave Luce had partnered with Melville
Clark Jr to design a TOS polyphonic keyboard.  I haven't yet read the
patent descriptions (US 4,365,533 and 3,969,968) but from the circuit
blocks it looks pretty convoluted (the description text runs 20-40 pages
long).  At Moog, Luce was tasked with designing the Polymoog; when Clark
learned of this he made angry infringement noises so Luce was forced to
design a Polymoog without infringing his work with Clark.  The Clark/Luce
patents were granted close to the Polymoog era, probably by Clark to
establish prior art in case of legal conflict.  No matter, nothing was ever
seen of the Clark/Luce polyphonic system nor was there any infringement
case ever filed.

The Polymoog did have one ace that the Clark system did not: the custom IC
under each key of the Polymoog which drastically reduced the size (and
cost) of a fully polyphonic synthesizer.

MC

On Thu, Jan 2, 2025 at 10:25 AM Roman Sowa via Synth-diy <
synth-diy at synth-diy.org> wrote:

> The thresholds in 40106, which define oscillator stability, are not even
> specified with regards to temperature or long term drift or any other
> drift. They may differ a lot from part to part, and nobody cares,
> because it's not the intention  of 40106 to be a timing device. Its
> operation relies on Vgs voltages and who knows what else, and that
> voltage greatly depends on temperature.
>
> Sure it's nice simple oscillator, like many others, but not all of them
> would be my first choice for tuning source. But for a drone, why not.
> Last year I've made a board which contains 24 such oscillators, voltage
> controlled, for a drone. And it's less than 1 inch squared.
>
> Roman
>
>
> W dniu 2024-12-30 o 19:49, David G Dixon pisze:
> > A CD40106 oscillator is just a schmitt trigger, a cap, and a resistor.
> > Presuming the supplied voltages are well regulated and the caps are of
> > decent quality, then why should one expect anything other than perfect
> > stability?  If I were looking for fixed-frequency square-wave
> > oscillators, that would also be my first choice, cuz it's so simple, and
> > one can fit all 12 oscillators onto a board that's about 4 inches
> > squared, even with through-hole components.
> >
> > ------------------------------------------------------------------------
> > *From:* Synth-diy [mailto:synth-diy-bounces at synth-diy.org] *On Behalf
> Of
> > *Roman via Synth-diy
> > *Sent:* Monday, December 30, 2024 12:01 AM
> > *Cc:* synth-diy at synth-diy org
> > *Subject:* Re: [sdiy] Interesting article on top octave generators.
> >
> > Not only from the 70's. There's this one guy who makes combo organ
> > eurorack module the hard way, with TOG, dividers and discrete circuitry
> > all the way down from there. He uses 12 tunable oscillators. And what is
> > most surprising, he uses 2 hex Schmit hex inverter chips for that
> > without any problems of stability.
> >
> >
> > Roman
> >
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