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Korg MS20M & SQ1

Analogue Synthesizer & Sequencer By Paul Nagle
Published May 2015

Korg MS20M & SQ1

The Korg MS20 rides again... again! The latest version takes the form of an expanded desktop module with accompanying sequencer.

Korg MS20s are like buses these days — you wait ages for one, then three arrive in short succession! The MS20M is another limited-edition DIY kit, its lack of keyboard and mod wheel offset against expanded synthesis power, an improved MIDI spec and a slim desktop design. It’s almost as if Korg are reimagining the MS20 in stages, each offering slightly more than the last. To further differentiate it from the reissues so far, this version is bundled with a little sequencer called the SQ1. Indeed, you can’t purchase an MS20M by itself, although the SQ1 is available separately.


My first sight of the MS20M was as a large box full of bubble-wrapped circuit boards, nuts, knobs and pieces of chassis. I must confess that unlike Gordon Reid, who carefully assembled the earlier MS20 kit with gloves on, I gave in to eagerness, spreading the parts and instructions across the floor and setting to without even putting the kettle on. Probably as a result of this impetuous approach, it took me almost two hours to put the MS20M together. Admittedly, part of that time was spent removing all the nuts I’d painstakingly secured on the patch panel in order to fit the bag of washers discovered under the dog. The instructions are very easy to follow, but I won’t deny that I’d have fared better had I put in some study, instead of scanning them complacently as I went along.

Having assembled a few offerings from Ikea over the years, I did at least count all the bits beforehand. The components seemed to be of high quality and I struggled only once, when fitting the triple junction box. In this, I had to resort to a pair of pliers because some of the nuts were too tight to fit by hand. A handy box-end wrench is included in the package, along with a mini-wrench that attaches the knurled nuts of the 3.5mm adaptor jacks. Otherwise, all you’ll need to find is a Phillips screwdriver and possibly a pair of pliers should you, too, be troubled by tight nuts.

A kit it may be, but other than a few sticky marks from excited fingers, there should be no giveaway signs once it’s complete. The two slimline but weighty steel sheets that form the body’s main structure are rigid enough and more carefully printed than the original MS20. Since this enclosure is less roomy than the rest, it was a relief that the boards fitted so snugly together and I found it infinitely satisfying to finally attach all the knobs and shiny wooden end cheeks, power on, and see those (brighter than vintage) red LEDs spring into life. I think I can state with some authority that if I can put the MS20M together, the instructions must be practically foolproof — as long as you follow them! Would I have preferred to simply open the box and start playing with a completed synth right away? Of course I would!

It’s possible that, in the excitement to get screwing and attaching, you might overlook the other item in the package. Fortunately, the small, Volca-like SQ1 ships fully assembled and ready for sequencing action. Lastly, you’ll find a bag containing 10 full-sized and three baby-sized patch cables, plus a copy of the original manual and patch book. Be aware that attempts to follow the supplied patching examples might tax you at first because they’re based on the former panel layout.

M Is For Module

In its desktop form, the MS20M is slender and chic compared to my old and gently rusting MS20. Placed side by side, the finished kit is a little over 2cm wider than the original and at just 587 x 211 x 104 mm, too long for a 19-inch rack, which would surely have been the ultimate ‘M’ format. Instead, yet another slice of ever-dwindling desk space must be reserved, possibly along with a shelf or support if you prefer the classic MS20 angle (or simply dislike the thought of objects dropping inadvertently into the patch sockets). The weight is a substantial 4kg and the power supply is an external line-lump type.

The MS20M is one of a growing army of recent devices that must be switched on individually, rather than by the single-switch approach used in many studios. If this trend continues, the wait before our hardware is operational will begin to rival the boot-up time of a Mac or PC! In use, the knobs and switches feel great and even the smaller knobs offer plenty of precision, trouncing the MS20 Mini in tasks such as accurately tuning VCO2, for example. Similarly, the many quarter-inch jack sockets feel like they’ll last for years.

The MS20M in its component parts.The MS20M in its component parts.Having already created a full-sized MS20 kit, it might seem a strange decision for Korg to repeat the exercise, hacking a performance synth into a module, so it’s a good thing they did more than that! As Gordon mentioned in his review of the previous kit, there were already modifications to the main board ready to provide oscillator sync, PWM and so on, but only now have these have made it onto the panel as fully fledged features. The MS20M is therefore not just a keyboardless MS20: it’s a souped-up, modified MS20, loaded with most of the wishes long-term users have yearned for but, until now, had to implement themselves. There’s also one baffling omission, but we’ll come to that.

In With The New

Rather than cover the same ground as existing reviews, I’ll assume some prior MS20 knowledge and concentrate instead on the enhancements that have blossomed in the MS20M. There are plenty of these, some of which are more obvious than others.

Three switches have sprouted on the panel, offering oscillator sync, FM and a choice of two filter revisions. Extra patch points have appeared, for example supplying an input for pulse-width modulation and the previously unavailable positive output of the second envelope. Finally, three junction connections (in the form of four-way multis) are located on the sloping area below the patchbay. In the MS range, these were previously seen only on the MS50; they’re ideal for, amongst other things, sending a single modulation source to multiple destinations. Each group of four joined sockets includes a mini-jack. Not only is this essential if you’re to use the included SQ1 sequencer, it’s also desirable for interaction with Eurorack gear or the MS20 Mini. A row of 14 unused quarter-inch sockets are blanked off but conveniently set aside for future modifications.

Even though there’s no keyboard, the panel still provides outputs for CV and gate (historically labelled ‘Trig’), but sadly there’s no mod-wheel output. Having encountered this useful feature recently on the Dreadbox Erebus (the mod wheel CV plucked from incoming MIDI), it’s a pity not to find it here too. As it is, it’s not quite so straightforward to translate favourite performance techniques from the classic MS20. Occupying the former position of the mod wheel’s output is the trigger switch, once the mod wheel’s trusty companion. It has been shunted to the panel in a move that could be simple expediency or a rare nod to left-handed players. With no jack plugged into its output, the switch triggers a note (C) so you can audition or perhaps tune the synth without making other connections.

The finished article’s front panel measures 587 x 211 mm — a  little too wide for a  19-inch rack.The finished article’s front panel measures 587 x 211 mm — a little too wide for a 19-inch rack.In a move I, for one, didn’t see coming, Korg have added an Octave/Volt CV input beneath the usual (for them) Hz/Volt in. Completing this cross-compatibility move, a second socket provides a V-Trig input, making the MS20M an ideal partner for a variety of analogue keyboards. I played it from both an MS20 and a Roland SH101, and I would have been perfectly satisfied with either. Unfortunately, however, adding the Oct/V input meant the old Trig input had to move aside, which in turn left no space for an important CV socket.

On every other MS20 model, you’ll find a separate CV input for VCO2, which means that on every MS20 except this, you can program sequences with two completely independent pitches. Or, if armed with a suitable CV keyboard, achieve duophony. I found it strange, bordering on bonkers, that the luxury of twin CV/Gate standards comes at this cost. It’s even harder to understand when you start to explore the oscillator sync function, which is exactly what I did next, flicking the first of the new switches.

Sync refers to the synchronisation of VCO2 to VCO1, and at a stroke it brings new expanses of biting raunchiness to this spiky filth-bucket of a synth. Once activated, a manual tweak of VCO2’s tuning control is all that’s required to unleash a bold, strident sync. Seeking a way of binding this effect to the movement of an envelope or LFO, I scanned the brief manual and noticed at least one of these was possible, but only as a by-product of another switch, FM.

When you activate FM, several things happen. Firstly, VCO1 becomes a frequency-modulation source for VCO2, the amount set by the ‘MG/T.Ext’ knob. Secondly, the VCO pitch component of the ‘Total’ input jack is disconnected, denying at a cruel stroke the opportunity for voltage-controlled FM intensity. Thirdly, and significantly for oscillator sync, the ‘EG1/Ext’ amount knob now points exclusively at VCO2. In other words, only with FM active can you enjoy envelope-swept sync.

A little later I discovered that it is possible to access VCO2’s frequency in (almost) isolation, despite the loss of the dedicated CV input. It’s not clear from the manual, but when FM is active, the ‘Freq’ input (which ordinarily affects both VCOs) only affects VCO2. Now you can pipe in an LFO or other modulation source without disturbing the pitch of VCO1, although CV received at the main input still drives both in parallel.

By combining sync and FM, your MS20M can spit and spark like no ordinary MS20 can dream of. Sourced from whatever waveform is selected for VCO1, the atonal and often metallic FM is going to attract lots of fans. An hour later and several dozen nasty metal percussion samples harvested, I realised I was one of them. The only trick missed here is filter FM, which could be an early candidate for user modification.

Continuing the theme of extending the MS20’s known audio palette, the third new switch could be the tipping point for the undecided. Unlike the MS20 kit, which used an internal jumper to provide access to both revisions of the filter, the MS20M’s switch seems far more musician-friendly. I’d never had the opportunity to A/B the two filters before, but within seconds I had a favourite. The Rev 1 is a killer — and at high volume almost literally. There were times when its resonance was so dominant that I was drawn back into electronic percussion, particularly towards dirty, unstable kick drums achieved with the cutoff frequency set low, resonance near maximum and a full-bodied zap from envelope 2. If you’ve ever doubted the MS20’s capacity for dangerous bottom end, the Rev 1 filter should settle the matter forever.

It’s been mentioned before that the earlier filter is a tad noisy — and so it is — but this barely detracts from its value. In contrast, the Rev 2 filter is more refined and controlled, its resonance exhibiting a shimmering, ringing quality that is a pleasant alternative to the bitter and often distorted harmonic mess of the older version. In the end, both are excellent, and there’s no doubt you’re spoilt by having the choice.

At the back we find the 12V DC external PSU input, a  MIDI In port and a  USB B socket. At the back we find the 12V DC external PSU input, a MIDI In port and a USB B socket. The last of the synthesis upgrades is PWM. It’s only available to VCO1 and even then, not until you connect a modulation source to the PWM input. The pulse-width control becomes PWM intensity and adds a degree of richness that previously gave a major ‘fleshing-out’ boost to the lowly MS10. Well, now an MS20 has it too, which can only be good.


Once upon a time Korg made an analogue step sequencer called the SQ10. With its three rows of 12 unquantised steps it wasn’t the finest example of the genre, but it scored by matching the MS10/20/50 in style — and by being more affordable than the ARP 1621.

Korg have chosen not to reinvent the SQ10, at least for the time being. Instead they took a different path, producing the tiny, battery-powered SQ1, a black metal box with squishy rubber buttons. At 193 x 84 x 63 mm, this brick-like sequencer has eight mini-jacks that dispense CV and gate, plus sync in and out signals suitable to match up with a Korg Volca or the new Electribe. The MIDI output is also a mini-jack and therefore requires the same adaptor seen on the Electribe. A further output is reserved for owners of the LittleBits range of modules, but those looking for the more generally useful MIDI input will be disappointed. This is a limiting omission and perhaps represents a cunning plan to sell more Volcas, which have both a MIDI input and a sync output.

With no power supply or adaptor, the only other connection is the rear-mounted USB port. This will power the SQ1 when connected to a computer or to a generic USB charger, if you have one. Two AA batteries are included, but I exhausted them in a couple of sessions. Either the quoted battery life of approximately five hours is highly optimistic or I genuinely lost track of time.

The SQ1 is a typical step sequencer of variable configuration, offering two rows (A&B) of up to eight steps. There are eight Sequencer Modes available, and if you switch to a different mode during playback, the sequencer is reset. The first of these modes, indicated by a saw-like icon, playback alternates between the rows, zig-zagging through the active steps. Next, offering more conventional motion, the ‘Zorro’ icon represents a single sequence up to 16 steps long. Continue around the dial and this is divided into two parallel eight-note sequences running forwards, or in pendulum mode (bouncing backwards and forwards). CV Duty mode is notable because row B’s knobs are used to set the gate length for individual steps. This is particularly nice for adding ‘feel’ and breaking a pattern’s rigid pulses, simultaneously giving some of us a pang of SQ10 nostalgia.

Another click selects ‘CV Slide’, in which the lower row determines the amount of slide between the voltages generated above. The result is 303-like, but offers more control. When combined with a howling MS20M bass line, it could become the SQ1’s most popular mode. Two random directions complete the switch’s rotation. The first of these involves Duty, with the lower row once again setting each step’s gate length. On the final position, two independent rows select their steps at random.

The SQ1 is certainly compact, but would make a  fearsome weapon if combined with a  sock. The SQ1 is certainly compact, but would make a fearsome weapon if combined with a sock. Korg invite us to assimilate yet more modes of operation, thanks to four choices of functionality for the step keys. Press the Mode button and an LED lights up to indicate whether the step keys control gate on/off status, determine whether steps are skipped, or are used to add slides. The last option, Step Jump, moves playback to any selected step and is handy either as a performance variation or for resynchronisation with other gear.

Even moments of fuzzy nostalgia never quite erase the memories of tuning each step of an SQ10 sequence. Happily, this needn’t be painful here, despite the Volca-style mini-knobs. By means of the Function button, you’re able to select the most suitable voltage range for each row and take advantage of a couple of built-in scales (major or minor). Unless you pick the ‘Linear’ option, the SQ1’s CV output will always be quantised and you can therefore expect accurate notes every time. Granted there isn’t the same visual feedback as the knobs of a larger step sequencer and the two scales are assumed to be ‘C’, but it’s not bad, all things considered.

Lifted directly from the SQ10, the Duty knob is used to specify the overall gate length. Its output ranges from very short percussive blips up to almost legato phrasing, but when either of the Duty modes is selected for sequence playback, the knob has no function.

MIDI-wise, the SQ1 is a close match for the MS20M because its spec is unspectacular. It can send notes on any consecutive pair of MIDI channels and responds to MIDI start and stop commands received over USB, but that’s about it. According to my Mac there are two USB MIDI ports: ‘SQ1 MIDI Out’ and ‘SQ1 CTRL’. The latter is intended to control the sequencer’s transport from your DAW, but there’s a bug in the current version in which the SQ1 stops sending notes as soon as it’s remotely started.


The MS20M is a thing of rare beauty and even to someone like myself, barely capable of assembling a sandwich, there’s no denying the DIY angle brings you closer to your new instrument. Whether this model represents the ultimate MS20 probably boils down to the importance you assign to having an attached keyboard, to the idea of playing a complete instrument. With both popular CV and gate standards provided, plus MIDI on any channel, at least it shouldn’t be difficult to find a suitable controller.

PWM, FM and sync are brilliant enhancements to a synth that was already as cutting as a dirty razor. Ditto the option to switch in the gnarly Rev 1 filter and unleash its unholy resonance. However, just when Korg had almost wrapped it up, having delivered the mods most popularly requested, they somehow managed to fumble it slightly. In the rush to add the goodies, they dropped the VCO2 pitch input. On the original, the moment you plugged a jack into this, VCO2 was neatly cut from the combined CV input and thus you had individual control over both oscillators. On the MS20M, this doesn’t happen and although there’s a partial solution, it isn’t as versatile.

Turning to the SQ1, it’s a powerful sequencer in a tiny package and could be attractive as a stand-alone device. However, taken together, the MS20M and SQ1 are an odd couple, mismatched in size, style and usability. This is not a cheap package and personally I’d have preferred to save a few quid and choose my own sequencer. Visually and performance-wise, the SQ1 is a better fit for the MS20 Mini. However, if you can get past a few incongruities, the addition of a ready source of extra voltages is welcome, even if the SQ1’s lack of MIDI sync is always going to be a let-down.

Summing up is easy. The MS20M is as wild, ripping and awesome as the original, but is capable of a range of tones no unmodified MS20 can equal. Further modifications are, of course, at the user’s discretion but there’s a sense of genuine encouragement inspired by those blanked-off sockets. Without a keyboard and mod wheel it’s hard to rate this as the ‘best’ MS20 ever, but it’s equally hard to think of any version I’d currently rate above it.


While not strictly filed under ‘new features’ there’s one last enhancement to consider, and it addresses an issue dear to my heart. The MS20M has been dragged screaming into the mid-1980s. Now, instead of being confined to MIDI channel 1, you can choose any of the 16. To perform this radical voodoo, you power on with a lead connected to the VCA output, then press the switch a number of times corresponding to the channel you want. Pulling out the lead stores the value, a process I doubt anyone will consider too arduous.

That’s practically all there is to say about a MIDI spec best described as ‘bare bones’. It seems an opportunity missed not to have added CV translation of velocity, pitch-bend, mod wheel and so on to those spare patch points, as is done on modern synths such as the Doepfer Dark Energy. As per MS20 Kit and Mini, MIDI is also available via USB and there’s no Thru.


  • It’s an MS20 with extras: PWM, sync, FM and a choice of filter revisions!
  • It is no longer stuck on MIDI channel 1.
  • The patch panel has been extended for wider connectivity.
  • Features three sets of multis.


  • Misses a few MS20 familiar options, such as a separate CV input for VCO2 and a mod-wheel output.
  • No option to purchase without the SQ1.
  • It’s a different instrument without a keyboard.


This is the most versatile and powerful MS20 yet, its reclining, slimline form unlike others in the MS range. It’s not cheap and you have to assemble it yourself but for many this will be the best incarnation to date.


MS20M + SQ1 £939, SQ1 £79.00. Prices include VAT.

Korg UK +44 (0)1908 304600

MS20M + SQ1 $1199, SQ1 $99.99.

Korg US +1 631 390 6800