image courtesy of Kevin Lightner

The Xpander was Oberheim's first synth product that was designed from the ground up with MIDI in mind. It was a 6-voice, multitimbral analog synthesizer with an extremely flexible design. Each voice or group of voices could either be assigned to respond to a specific MIDI channel (1-16), to a specific keyboard range on a specific MIDI channel, or to any of 6 CV/Gate (1volt/octave) inputs. The output of each voice could be panned separately (7-positions) in the stereo output, or accessed individually through their own separate direct output. The Xpander also had a mono (summed stereo) output.

Each voice consisted of 2 VCOs (triangle, saw, pulse, or noise, VCO2 could be synced to VCO1), a multimode VCF (low-pass, band-pass, notch-pass, high-pass and four "combination" filter modes), and 4 VCA's (in line one after each oscillator and two after the VCF). FM of VCO1 and the VCF was possible via VCO1. The filters could also be set as 1-pole (6dB/octave), 2-pole (12dB/octave), 3-pole (18dB/octave), or 4-pole (24dB/octave). All oscillators and filters could be tuned by a handy auto-tuned routine. In addition to this basic synth engine, the Xpander had a number of separate modules that could be inserted in any modulation path. These include (5) LFO's with basic waves plus sample-and-hold and random functions, 3 tracking generators, 3 ramp generators, a lag processor (does not necessarily have to be used for portamento), and 1 additional global LFO to be used with the Mod Wheel.

You could store 100 program patches and then set up an additional 100 multi-timbre setups storing any of those patches on each of the 6 voices, panning them and assigning how each voice is controlled. Patches could be dumped to cassette or via MIDI sys-exe.