MOTM

> >> apart from the EFM boolean logic module, does anyone 
> know of any  
> other synth manufactuer who makes a similar thing (Emu 
> excepted) 

I'm not a synth manufacturer, but here's a little "VariLogic"
circuit of mine:
http://home.t-online.de/home/jhaible/hjvarlog.gif

It can be switched to AND, OR, XOR, NAND, NOR and XNOR with
one on/off/on switch and one on/on switch.

A simple INV fuction is possible, too, as the inputs are normalized.

Input A is normalized to "High", and you can connect a
simple footswitch here to provide one of the input signals.

The circuit works without a separate 5V supply, and it's quite
sturdy when it comes to overvoltage, ESD and so on (no CMOS
chips).

LEDs for inputs and outputs, of course.

JH.