Matrix-12 control repairs

Once again, a repair documentation just for the sake of having these bits of info written down somewhere. Notebook as good as any ;) .. Just to intro this monster of a synth, here’s what Peter Forrest writes about it in his book “A-Z of Analogue Synthesizers“:

The Matrix-12 is a 61-note synth with three big LCDs, six value knobs and about 60 switches on the front panel. Internally, it is 12-voice polyphonic and 12-part multitimbral, each part responding to its own MIDI channel. Each voice provides two big fat VCOs (offering triangle, saw, pulse, and noise waveforms), one 15-mode VCF (offering various low pass, high pass, band pass, notch and phaser types, all complete with resonant squelch), five LFOs, five envelope generators, 15(!) VCAs, and one FM modulation generator for oscillator sync and cross-mod madness.

There’s also a lag generator (a sort of portamento that can be applied to anything, not just pitch), three keyboard-tracking generators, four ramp generators (a very simple two-level envelope) and, finally, one noise generator. And that’s just one voice. There are 12 inside here! All this sound-creating muscle is useless without an equally powerful control system, and to this end Oberheim came up with the ‘Modulation Matrix’ from which the machine takes its name. This system enables 20 connections per voice between virtually any parameters. For example, to increase the speed of an LFO with time, select LFO speed as the destination and a slow attacking envelope as the modulator.

The Matrix-12 that landed on my desk was in need of lever potentiometer and rotary encoder replacements. As is, the lever potentiometers had problems tracking smoothly (eg. resulting in pitch “warble”) whereas the encoders did a lot of skipping back and forth.. Working but unusable, so to say.