Both of the mixers in the CGS dual ETI 414 master mixer started out life as the output stages of an ETI 414 master mixer, a project of the same vintage as the ETI International 4600 synthesizer. In fact there was very little difference between the 4600 equalizer and those used in the mixer.
The mixer equalizers were designed to work on a single +30 volt supply, as distinct from the +/- 14 of the International synthesizer. They also used 741's instead of 301's. The important part, the five pot-core based inductors used in each were identical.
It was a simple matter to move a few parts around on the PCB, cut a few tracks etc., to convert one circuit to the other.
Readers are permitted to construct these circuits for their own personal use only. Ken Stone retains all rights to his work.
Five band Equalizer for music synthesizers. by Ken Stone, 1999, with permission of the author - archived
- ETI Master Mixer, part 1-4, ETI, Apr.-Jul. 1973
- ETI Master Mixer Modification, ETI, Oct. 1973, p.52