Korg MS-20

The MS-20 is a monophonic patchable analogue subtractive synthesizer, produced by Korg in 1978.

Technical

Schematics

Does anyone have better scans of the service manual than the ones on Ben Ward's site ?

Internal wiring

HeaderWire harness
H14 × brown
H27 × red
H38 × orange
H43 × yellow
H53 × green
H63 × blue
H7brown black orange

See also Kevin Lightner's photos.

The connectors were made by JST. Closest match in their current offer seems to be the NH series (pitch 2.50 mm). Digi-key reference a bunch of JST NH parts but only stock the female contacts (SHF-001T-0.8BS) and 3-position housings (H3P-SHF-AA). In a pinch, 0.1" AMP MTA and Molex Mini-KK connectors seem to mate with the JST connectors (but do not lock as the keying is different).

Power transformer

According to BDB2747E984D4833BCE2A9093526EC77@T41 (Ko/Modeless Factory 2012-09-18), the North American models had a single 120 V primary while the rest of the world had a three-tap primary : brown wire for 100 V, orange wire for 220 V and yellow wire for 240 V. Mine is a 220 V model and the transformer (stamped KA-221) matches that description : four wires on the primary, mains between black and orange.

Secondary is centre-tapped, most probably 18-0-18 V (see synth-diy thread). Rated power unknown.

Bad IC5 causes pitch instability

Over the years, my MS-20 developed a wavering. The cure was to replace IC5 (CA3140). See the thread on the synth-diy list (part 1, part 2, part 3, part 4 (two messages missing), part 5).

Other

Sounds

Unless otherwise noted, all recordings are of my MS-20, which has the earlier KORG35-based filters, not the later LM13600-based ones.


This is http://www.teaser.fr/~amajorel/ms20/, last modified 2014-03-30.