The Korg MS-20 Retro Expansion is my heavily modded version of the Mini version, although the mods would also work on the original model. If you're interested in adding any of these mods to your own MS-20, I've described all details of the circuit changes and added more photos of my synth on my web site:  www.yewtreemagic.co.uk/soundworlds3.php

The Retro Expansion includes the following additional features:

1. MULTI-OUTPUTS: To supplement the existing choice of one of four OSC1 waveforms I added separate TRI, SAW and PULSE output sockets, all available simultaneously, plus a separate output for OSC2.

2. PWM: Next up was an additional input for OSC1 variable pulse width modulation, using the existing pulse width knob to control PWM level. 

3. SYNC & FM: A Sync toggle switch was added to OSC2, to lock it with OSC1 for those screaming lead sync FX.

4. An FM input was added to OSC2 with its own rotary level control, so it could be modulated at audio rates by OSC1 among other options.

5. VCO MIXER: I also expanded the existing mixer section, adding two extra input sockets, each with its own level control knob. These can be used to mix together several oscillator waveforms, or to mix in other patchbay or external audio signals.

6. I also added a more traditional transformer/schottky diode ring modulator circuit to achieve far more mellow ring mod options than the integral (XOR) option.

7. Final casework mods included a new top-mounting panel for all the new controls, a 1/4-inch jack output, and cherry hardwood side panels.

I'm well pleased with the results - enjoy!

Martin Walker

Sync, FM & Ring Mod

Martin Walker is well known for his music and sound effects design on over a hundred game soundtracks, and for his columns and features on sound design in magazines such as Sound On Sound and Audio Technology.

Sync, FM & Ring Mod

Yew Tree Magic