A monophonic analog semi-modular synthesizer with a 36-note keyboard. Essentially a scaled down version of the PS series' huge patchable synths. Approximately 10 000 units were manufactured between 1978 and the early 80s.

The MS-20 features 2 VCOs with a noise generator per voice. Available waveforms for the VCO1 are triangle, sawtooth, variable pulse and white noise. VCO2 (which is scaled an octave higher than VCO1) offers sawtooth, square, narrow pulse and a ring modulator. Independent level controls for both oscillators are available, and their pitch can be modulated by either the LFO or the envelope generators.

For filters, the MS-20 has two 12dB/octave multi-mode VCFs capable of high-pass, notch and band-reject modes with independent resonance controls. The VCFs can be modulated by the LFO and shaped with the EGs. External sounds can also be routed through the unique filter section.

The LFO features multiple waveforms and full control over modulation speed. There are 2 envelope generators: EG1 is internally routed to the VCOs and features delay, attack and release. EG2 is generally used for shaping the VCF/VCA, and offers an ADSR envelope with hold.

Both hard wired and patchable connections are included, much like in ARP 2600. The main panel consists of several clearly marked knobs and a small patch bay. An assignable mod wheel is also available.
Interfacing with other synths is a problem, since the MS-20 uses Hz-to-voltage (for oscillator stability) instead of the volt-per-octave standard. Third party converters have been made to solve this issue.
Numerous accessories were made, including the MS-01 foot pedal and the SQ-10 sequencer which could also store MS-20 sounds. A cheaper little brother, MS-10 was also released.

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