[sdiy] Analog polyphony question

[Don Tillman]

   From: "Dr Strangelove" <phdinfunk at hotmail.com>
   Date: Sun, 12 Aug 2001 23:27:58 -0400

   I was reading recently about TOS based organs, Thomas Organ Co.,
   Farfisa, Wersi, etc, The Vox Jaguar used a similer approach but
   didn't use a TOS IC so it didn't have JUST square waves I think.

What did the Vox Jaguar do?

Note that you're not stuck with square waves just because square waves
come out of the dividers.  You can sum octaves of square waves to get
a staircase, or you can use a cap, diode and resistor to get a half
exponential sawtooth.  The PolyMoog actually performs PWM on the
waves.

   Basically the TOS ICs would divide a 1 or 2 Mhz square wave down to
   create the top octave then they would have other ICs to divide by
   2, 4, 8, 16 etc for the lower octaves, If you could tune the 1 or 2
   Mhz square wave then you could detune two TOS organs from each
   other, which would be kinda cool.

The PolyMoog does this.  In several different ways.

Another thing that the PolyMoog does is that it uses different divider
taps on the two Top Octave Generator ICs -- the second TOG chip is
clocked one semitone higher than the first TOG chip, and the outputs
are all corresponding shifted down a semitone.  This means that there
won't be an unnatural sync between the two TOG chips.  That's very
clever.

(More details on my Moog Patents page:
  http://www.till.com/articles/moog/patents.html)

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com