Synthesis Technology MOTM-190 Dual VCA + Ring Modulator (DIY)

The MOTM-190 is a dual VCA in a compact 1U format. VCA #1 can also be used as a Ring Modulator.
Also known as the uVCA... (microVCA)

The full kit is compatible with the dotcom/MU format standards-- bent aluminum panels w/black powdercoat/white silkscreen (made by Freestate FX) and include the 3-pot MOTM bracket for easy PCB mounting to the panel 

VCA #1: VCA / RING MOD

The top knob (marked Blend) and switch (marked V and R) control VCA #1. If the switch is in the 'V' position, the circuit is a linear VCA. The Blend control acts as an Initial Gain control, normalized to unity. If Blend is all the way to the left (the IN position), the gain is unity ('1') and there is no modulation (the output equals the input). As the Blend knob is turned clockwise, more and more of the CV modulates the signal. Fully clockwise (the RM position), the CV changes the gain from 0 to 1. This is "standard" VCA operation.

If the switch is in the 'R' position, the circuit is a Ring Modulator. The Blend control acts the same way as a Yamaha CS-80: all the way to the left, the output = the input. As Blend is turned to the 'RM' position, the depth of the Ring Mod effect increases.

VCA #2: STANDARD VCA

The second VCA is switchable between Linear and Exponential responses. The Gain control sets the initial gain from 0 to 1. The CV Mod control ajusts the depth of AM for the VCA (in normal operation, the Gain is set to '0' and the CV Mod is set to '10').

Although "micro" in size, the MOTM-190 is a low-noise, low distortion, high dynamic range (better than 100dB) dual VCA. The Ring Modulator Blend control is not currently found on any other modular.

Demos (courtesy of Paul Schreiber, using original MOTM format):
Aliens!
Ring mod effect with 2 sine waves, vary
All sorts of ring mod and percussive effects