Oberheim Two Voice

If any synthesizer can be considered to be greater than the sum of its parts, it’s Tom Oberheim’s enduring classic, the Two Voice.

The Oberheim Two Voice (or TVS‑1) is one of Tom Oberheim’s favourite creations from his impressive back catalogue. Born out of a humble satellite unit designed by an all‑star cast of engineers, the Two Voice was the beginning of a line of synthesizers that have made an indelible mark in contemporary music.

An Engineer Finds Music

A Kansas native with an interest in electronics, Oberheim moved to LA with friends in the 1950s. As well as experiencing printed circuit boards for the first time whilst working for a camera shop, he also took a role as a draftsman for the electronics division of National Cash Register, who were one of the earliest companies to build computers.

Realising he needed to study further to get where he wanted to be in an ever-changing technological world, Oberheim returned to education, studying Physics at UCLA in his 20s. This, fatefully, included a side course in art and music. Developing an appreciation for music through his studies, Oberheim started singing in choirs, including the UCLA choir. This moved him into circles of musicians and one day, one such musician asked Oberheim if he could use his skills to build him a ring modulator. Not really knowing what a ring modulator even was, Oberheim found an article written by Harald Bode, famously a collaborator of Robert Moog, and successfully managed to build a working device in his apartment in Santa Monica.

Word of this must have spread as Oberheim then received a phone call from composer Leonard Rosenman, asking if he could bring a ring modulator down for use on a film he was scoring, which turned out to be Beneath The Planet Of The Apes. Whilst the ring modulator was only used on some piano parts, musicians in the orchestra were intrigued by the device and asked if he could sell them one so, still based in his apartment, he went into business.

Oberheim then got a call from Chicago Music Instruments (CMI), who’d also heard of his ring modulator and wanted to add it to their Maestro line of effects. And so it became the Maestro RM‑1, which is why both Oberheim and Maestro badged versions of the same effect can be found.

Spurred on, Oberheim then decided to try to build a pedal that emulated tape flange, but came across an example circuit for phase‑shifting using op‑amps and so built that instead. Again, Maestro added it to their line and it became the Maestro PS‑1A, which sold a staggering 70,000 units in the 1970s, putting Oberheim well and truly on the map.

Pulling on his earlier experience working with computers, Oberheim then designed one of the earliest digital synthesizer sequencers on the market in 1973. The DS‑2 stored control voltages in logic gates and could then play them back to reproduce the programmed sequence of notes. Unlike the first microprocessor‑controlled sequencers, such as the Roland MC‑8, there was no ability to copy and paste or sequence multiple tracks, but the possibility of storing 144 notes in a world of 16‑step sequencers was a big deal for the time.

For all its exciting potential, however, the DS‑2 created a problem: if a synthesist hooked up their synthesizer to it to play back a sequence, then what would the synthesist play? This realisation lead Oberheim to begin work on a satellite synthesizer unit that could be used with the DS‑2 whilst the synthesist played along on the keyboard of their main synth. For this idea to sell, the satellite unit needed to be as affordable as possible, but also have the minimum required to make it usable.

The resulting design was dubbed the Synthesizer Expander Module, or SEM for short. It contained two oscillators, a state‑variable filter, an amplifier, two envelopes and an LFO. Deliberately designed without a keyboard, the rear of the unit housed the jack points to connect it up to the DS‑2....