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Korg MS-10 Notes

Posted under Musical Technology at . Last updated 2022-06-02 06:39.
Tags:instrument, MS-10, Korg, synthesiser

MS-10s need no introduction, so — here’s one. Probably from about 1980 but I haven’t got it far enough apart to look for component dates.

front (on arrival)

This arrived in a purportedly Pro-Serviced state. In contrast to my many other gripes on the topic, I must note that it was well-packed, and arrived faster than the estimated earliest date. Also in near-perfect physical condition, which for me is a first, for a synth without a case. So would buy again? Maybe. It doesn’t even smell bad. No rotting food or wildlife, no decaying components, no decades of garage-storage and no undead tobacco. [1]

But I’d like to know what Pro-Serviced means. Perhaps that this time I’m paying someone to do the things I would normally do myself? This clearly doesn’t include cleaning, past a cursory wipe; there’s a lot of dust ingrained on the modwheel and at the back of the keys.

More troublingly, while I bought this as 220/230V, it has an original factory label saying 100V. I have asked the seller about it. In the interim, comparing this with the identical (KA-680) transformer in the 220V-rated SQ-10, they both appear to be putting out almost exactly ∿20V, which is basically what you get when you run 240V into a 220:18V transformer. (The seller later confirms that they did change the tap, but didn’t put a label on to say so . . . confusing. I will make a label.)

It also came with a nearly-new plug. Its two pins are 4mm diameter, 19mm apart (centres), 16·5mm long, and don’t converge. It’s too loose in a standard shaver adaptor, but it seems good in a generic European plug adaptor. Interesting plug; I like the sheath clamp. I assume this is a French type, as it’s NF-marked, and is available on French retail sites, but I don’t see any references to the exact specification. I don’t think I can use it for anything. The cable is 2-core, of the type you see on old Japanese-market Korgs, so I expect that’s what this is. (Where else uses 100V?) In the interim I’ll put a BS1363 plug on, but upgrading the cable to 3-core would be good — as would a C-14 socket, but I have a stack of these to do.

supplied power plug, open

Opening up, there’s the expected dust in the base. And surprisingly little circuitry . . . the power regulator is integrated on the main circuit board. Difficult to get at this, as the case is a single folded sheet, and for the components side you need to undo all the pots. Oh well. Nothing urgent. The keyboard and modwheel plug into the end of the PCB; these are quite difficult connectors to remove, but it can be done. I haven’t tried disconnecting the jack field, as I expect it would be at least as delicate.

interior from below

Having checked voltage, I can reassemble and switch on, properly. It seems in reasonable condition, though there’s a lot of scratchy noise from somewhere when using the VCO triangle wave. The sort of thing that might come from random charging of caps that aren’t really doing anything, but aren’t really isolated? At a cursory glance there’s nothing here to indicate that the Servicing included getting the board out. It might have included recalibration, not sure. There are no signs of anything other than the transformer being touched, but calibration is done from outside, thanks to removable panel plugs. The key contact seems good, but there are no traces of interventions in the dust there either. All being well, on the morrow I’ll give it a proper clean-out and change the plug. And, yeah, probably would buy again.

(Pause for sleep and so on.)


The key/keybed design is probably the best I’ve ever seen. (Apparently Moog used them too at this time?) The keys are all plastic, and hence simply washable, but these are stronger. The natural and sharp keys use the same return spring, but position them slightly differently to equalise tension. The contacts are copper strips which are pressed down by a padded projection on the key. No fiddling with springs or wires here. The keybed is galvanised steel, bolted onto the also-steel lower case. Robust, easily maintainable. Couldn’t ask for much better, in fact. I am seriously reminded here of how Western European consumer goods manufacturing was practically wiped out by Japanese imports in the 70s and 80s. There were other factors, but this type of radical improvement in design and build quality, with cheapness and innovation, was a large part of it.

The keybed has rubber bushes, primarily for the return motion, and a felt strip for down. The bushes seem fine; the felt is a bit indented with use, and so a little harder than new, but not to the point where it really needs replacing. The contact projections also have small rubber bushes. Oddly, there are two colours, slightly different thicknesses, for the naturals and sharps, sharps being lighter and slightly thicker. It seems likely that the difference is intentional, but I’m not clear why it would be needed . . . 

key bushings

In replacing these after washing, the F3 bush split. I’m not sure whether replacements are available [2], but to be going on with I replaced it with two layers of heatshrink sheath. (3 layers for a sharp key, maybe?) There’s no apparent difference in the outcome.

key removed, showing bushing

Contact cleaning is straightforward, though you have to be a little careful not to trap the edges of the strips. Quite a bit of dirt came out. Maybe that would have been part of the Pro Service if it had really been necessary . . . These contact strips aren’t greased like some. I guess they’ve lasted oh, 35 years or so, without it.

keyboard cleaned


Basic outline: OFA (Oscillator, Filter, Amplifier — one of each), plus one transient modulator (Envelope Generator), one periodic modulator (Modulation Generator), and a noise source. The Oscillator transposes over four octaves, and generates triangle, sawtooth or rectangle [3] (with varying pulse width) waveforms. An external signal input can be mixed in with the oscillator at the filter stage. The Filter is Low-Pass, with variable self-oscillating Q. The EG is ADSR with a Hold control to set minimum ADS period. The MG waveform can vary from rising through triangle to falling sawtooth, or, as a patchable output, from thin-positive through square to thin-negative pulse-width. White noise can be substituted for the oscillator, and both white and pink are patchable outputs.

The MS-10 has some features you don’t tend to read about on the net:

  • Key priority is high.
  • It seems to be single-trigger / slur-mode only. (i.e. if a second key is pressed before the previous one is released, no new trigger signal is sent/detected, even if it’s higher-priority. Hence, no new envelope is triggered.) The EG Hold function does not delay the actual trigger-off, so it is nevertheless possible to get something like the effect of multi-triggering, with Hold long and Decay short.
  • This may not be normal, and might be fixable if not, but here at least the modulation generator doesn’t have quite enough power to drive two outputs at once — patch it into some other feature while you’re modulating the filter or oscillator, and you can hear the MG frequency drop.

Overall, if we ignore the patchbay, it’s probably the simplest synth I’ve ever used. The patchbay is also very simple, with some odd constraints. For a start, the envelope generator provides a patchable output for negative envelope, but not for positive, which is hardwired to Filter Cutoff and VCA. Amongst other things, this means that Pulse Width can be modulated by a negative but not a positive envelope.

There’s also some ambiguity around modulating the peak (rather than initial) volume of the amp stage. Fair to say, it’s not the most useful of effects; also fair to say, you can modulate the initial level by patching a source into the INITIAL GAIN input, which allows for part of the effect. Looking at this more carefully, it is possible to patch a source into the EXT SIGNAL IN port. The patchbay diagram suggests this only affects the filter, but the amp diagram on the control side suggests it should also affect the amp, so . . . Using the EXTERNAL SIGNAL LEVEL control as a mod level control, it does sort of work. But the EXT SIGNAL IN port is marked 3VPP, and the MG outs are 5VPP (−2·5V to +2·5V triangle, 0V to 5V rectangle). As you’d expect then, amp modulation can be overdriven, resulting in a weirdly diminished effect; but even at a lower setting (mark 4 seems about the maximum), there’s something odd, especially from square wave. It doesn’t sound very square, as though the modulation signal (or its effect) is being smoothed out somehow. I might need to get this on a scope to see what’s going on. So: possible, but still not the most useful of effects. But it does produce a sort of cute sound with the triangle wave, kind of like a really old analogue echo effect.

Anyhow, basically this synth is in almost perfect condition. No real issues to note. Play it.

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  1. The last keyboard I bought came from a tobacco and pet-free home, and true, the keyboard itself was moderately sweet-smelling, but it came wrapped in the bit of secondhand bubblewrap from the garage a certain someone must previously have used to hide their 2-pack-a-day habit from their kids throughout their formative years.  
  2. Update: Some sites are selling these bushes secondhand. Not what I had in mind; think I’ll stick to heatshrink.  
  3. Update 2022-06-02: I noticed earlier that while the waveform switches on Korg synthesisers of this era are mostly labelled with symbols, the manuals refer to rectangle rather than square waves, which is more sensible anyway, so I’ve corrected that in this article.  

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