At the start of 1975, Oberheim did not consider itself a synthesizer manufacturer. At the time, the company's business was comprised of contract manufacturing Maestro-branded effects units, as well its own products, the DS-2 digital music sequencer and Synthesizer Expansion Module, which were intended as add-ons for Minimoog and ARP 2600 owners. When Norlin canceled several large Maestro orders, the company was forced to develop new products to replace those lost sales. By combining multiple SEM synthesizer modules with a digitally-scanned keyboard developed by Dave Rossum and a two-channel sequencer, Oberheim created the Two Voice and Four Voice, the first two Oberheim Polyphonic Synthesizer models, and some of the first commercially-available polyphonic synthesizers.[2]
^Moog, Bob (1993). Vail, Mark (ed.). Vintage Synthesizers: Oberheim SEM Module. San Francisco, California, USA: Miller Freeman Books. pp. 151–156. ISBN0-87930-275-5.
^Forrest, Peter (1996). The A-Z of Analogue Synthesizers Part Two: N-Z. Devon, England: Susurreal. p. 22. ISBN0952437716.
