The first synth by Korg to make a significant impact in the Western Hemisphere nations, the MS-20 was a semi-modular, monophonic analog synth produced from 1978 through 1983. It occupied niche in synths available from the major manufacturers at the time; the voice architecture was comparable to the Minimoog, but it had a jack panel providing the semi-modular capability. As such, it was a considerably lower cost system than the comparable semi-modulars of the time such as the ARP 2600 and the EML 101.
The MS-20 contains two VCOs, high pass and low pass VCFs, and Korg's notorious single-transistor VCA. A dedicated LFO and two envelope generators are also included. An unusual feature is the external interface capability, which contains a pitch-to-control-voltage converter and an envelope follower. Many users of the MS-20 have taken advantage of these to drive the synth with other instruments and make bizarre noises (the pitch converter does not track all that well, and can produce very random results). The MS-20, like most early Korg designs, uses volts/Hz scaling, which makes it difficult to interface to equipment that uses the more common volts/octave method. The synth was packaged with a three-octave keyboard and a mod wheel, but no pitch wheel.
Korg produced two variants of the MS-20. The MS-10 was a stripped-down, single-VCO design with a 32-note, F-to-C keyboard. The MS-50 was sold as an expander for the other two; it added a VCO, VCF, VCA, two envelope generators, an LFO, and some unusual features such as an integrator and a moving-needle analog voltmeter. The MS-50 had no keyboard or other performance controls, besides a patchable manual gate button. Korg also offered the SQ-10, a 12-step analog sequencer that interfaced with any of the MS synths.
Today the MS-20 is frequently sought out by performers who often uses its filters and modulation capabilities to modify the sounds of other instruments. The MS-20's filters are considered particularly desirable and the circuit has been cloned by several modular synthesizer manufacturers.