The CGS mixer and ETI 4600 VCA module is the combination of two sub modules, a mixer and a voltage controlled amplifier.
For the construction details of the mixer, see the CGS DC mixer (previous version). In this case, only two inputs are used, and there is no overall gain control. The output is fed both to the output socket and the switched input of the VCA signal input (normalised connection).
The VCA itself is the VCA/Ring Modulator from the International 4600 (Maplin 4600).
Two have been constructed, and there is a third waiting for a panel. Two of these VCA boards were hand etched, and the third was one of the boards from the 3800.
Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.
VCA for music synthesizers. (archived) by Ken Stone, 1999, with permission of the author