A monophonic analog synth produced by Steiner-Parker from 1975 to 1979; it was probably the company's most popular product. It featured an architecture basically similar to the Minimoog, but with some additional features and many more signal routing options. It was designed using circuits from the company's Synthasystem modular synthesizer line. Notable features include the rows of small toggle switches that select routing options, and the unusual right-to-left presentation of the signal flow on the panel.
The synth contained three voltage controlled oscillators, like the Minimoog. There were many modulation options available; the VCOs could frequency modulate each other in various combinations, and all three could be modulated by one of the envelope generators or the sample and hold circuit. The voltage controlled amplifier could be modulated by VCO 3 for amplitude modulation effects. One envelope generator was dedicated to the VCA; the second one could be switched in parallel, allowing more complex amplitude envelopes. The envelope generators were ADSR in design, but one knob set both the decay and release time. A switch setting could override the release time and cause a fast release.
The synth contained the now-well-known Steiner filter VCF design. Designer Nyle Steiner wanted something different from the transistor ladder designs most synth manufacturers were using at the time. (Plus, he didn't want to pay royalties on Moog's transistor ladder patent, which was still in effect at the time.) The filter had a unique character and made the Synthacon notable, although it didn't exploit the filter's capability for multiple simultaneous inputs.
The synth had a 49-note, C-to-C keyboard, a longer span than many competing synths. The pitch wheel was a non-sprung knob on the panel, in the keyboard input section. Later production models had a duophonic keyboard; the second control voltage could be routed to one of the oscillators or to the filter. Apparently a few were also built with the "Multiphonic Keyboard", which contained an arpeggiator.
Steiner says "a few hundred" Synthacons were built. Derivatives include the Mincon, a cut-down single-VCO design, and the hand-held Microcon, which was originally designed to be used as part of a guitar synthesizer. Production continued until Steiner-Parker went out of business in 1979.