New DIY Polymoog Project - TOS Polysynth

via adamstan on electro-music.com:

"Hello

I've always wanted to have the Polymoog, however getting one isn't easy - and getting working one is even more difficult , and that beast is HUGE. So I decided to build something similar myself. As with my first synth, this is mix of many designs. Currently I'm designing last boards, and going to order them today or tomorrow morning. They should arrive in two weeks, and then - soldering mayhem But, back to the design itself - what will it be?

- 61 keys
- Master oscillator section based on Polymoog - two VCOs driving two divide-down ranks using PLL
- Dividers built with CMOS counters - 4040 with diodes & 4024 for each note, like in TOG thread by AnalogCustom http://electro-music.com/forum/topic-45583-0.html&postdays=0&postorder=asc&highlight= - this is the biggest board
- Waveshapers based on Polymoog too
- Digital envelopes and LFOs
- there will be 4 LFOs, like in Polymoog - one for each VCO, one for PWM and one for filter
- VCF & VCA from Korg PS-3100. Why? Because it has lowest parts count, that's why
- Polymoog resonators and maybe some 4-pole master VCF at the output.

I will post current schematics when I get back home today. Here is waveshaper simulation done in falstad circuit simulator:" [above]

Capacitors have to be selected for each note to provide consistent saw level & PWM range across entire keyboard.

The VCF/VCA modules will sit on small "articulator" cards, that will plug vertically into 5 motherboards (one for each octave). Each mobo will also have associated waveshaper and envelope card. So it will look like this:

Green bars are the articulators, red one is waveshapers, and blue ADSR.

The nice thing about this design is that it will have no ASICs/proprietary parts - just off-the-shelf op-amps, CMOS and TTL cirucits. And a bucketload of transistors of course (almost 600)"