The MS20 ringmodulator
The KORG MS20 Synthesizer contains a ringmodulator, modulating VCO1 and VCO2. Well, this ring modulator creates really good sounding, warm bells and metallic noises.
Calculating the original schematic will give Y=inv(inv(A) and B), which, of course, is not XOR and will sound not very spectacular. At least not at all like a ring modulator.
The original schematics seem to have a little error, the red spots in the KLM127 schematic is marking it : the left one stands for "connect the crossing", the right one for "invert"
Here is a short mp3 how it sounds :
And here, with different Frequencies for Osc1 and 2, some more samples :
I modified the schematics a little, now it can work with saw and triangle waves too (beside rectangular input signals). Of course, the two comparators after the Input 1 and 2 can be left away, if the input signal is a square wave. The 4011 was replaced by a 4030 XOR CMOS. Simpler to built !
Build up on a raster board, it looks like this :
PS: don't forget to decouple the 4030 !!!