The Moog Sonic Six is a 2-VCO duophonic synthesizer with a built-in speaker and a 4-octave, 49-note (C-C) keyboard. Each VCO can output sawtooth, triangle, and rectangle (pulse/square) waveforms as well as 2 "waveform generators." A "quality" knob adjusts the width of the rectangular waveform. White or pink noise is also available. The Sonic Six can be set for 3 keyboard modes; high note priority, low note priority, or duophonic. The Sonic Six can also be set to an alternate tuning across the keyboard (different interval between octaves of the keyboard). Portamento rate is controlled by a knob. The envelope section features a basic envelope, with variable control for attack and decay and a switchable release (follows decay) and sustain. It had a single VCF, low-pass voltage controlled filter. Two multimode LFOs are available. Their speed is independently variable and can be controlled by the envelope.
[from The A-Z of Analogue Synthesizers , by Peter Forrest, published by Susurreal Publishing, Devon, England, copyright 1994 Peter Forrest]
Michel Huygen of Neuronium,
Brian Kehew and Roger Manning of The Moog Cookbook,
Robert Moog - on his many lecture trips,
Mats Oberg playing with Frank Zappa,
Yes - 70's, the Relayer tour, Patrick Moraz had one
[Let us know if you have any further additions to this list.]