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Dave Smith Instruments Mopho X4

Analogue Synthesizer By Paul Nagle
Published June 2013

Dave Smith Instruments Mopho X4 synthesizer.

Dave Smith's latest synth crams four Mophos into one keyboard-shaped box. The result promises to be more than the sum of its parts.

Dave Smith Instruments have flourished since the small but perfectly-formed Evolver hit the streets a decade ago. In that time, DSI have extracted more mileage from Curtis chips than Tesco have extracted former Grand National runners from freezers. So while the Mopho X4 is brand new, it looks and sounds familiar. Less familiar is the act of blending multiple analogue voices, knobs and an aftertouch-enabled keyboard. Visiting uncharted regions, there's a dizzying expansion plan, plus a large patch library and equally large user pool. The Mopho X4 may not be physically huge, but it's a polyphonic synthesizer worthy of attention.


I won't shed any tears that the Mopho X4 isn't bathed in the daffodil yellow of previous Mophos. Neither will I particularly miss the printed overlays of the Evolver and Prophet 08 panels, replaced here by a traditional and undeniably more satisfying paint job. The Mopho X4 borrows its shadowy good looks from DSI's own subdued but chic Tetra synth module, and pairing them up is more than simply a cosmetic exercise. Placing a Tetra on the convenient space on the Mopho X4 panel and chaining the two together creates a cute yet powerful eight-voice synthesizer. Voice expansion can stretch as far as 16 voices, providing you keep buying hardware!

The Mopho X4 is exactly what its name suggests. It has the same analogue signal path as the Mopho Keyboard, but instead of one, it has four voices. Unlike the Tetra, those voices always play the same patch, because the Mopho-by-four is direct, performance-oriented and resolutely monotimbral. This didn't compromise Roland's Jupiter 4, and I doubt anyone will give it a second thought after playing the first few notes.

Aided by its rigid steel construction and end-cheeks of solid wood, this is a keyboard that should not fear life on the road. However, at first glance — and even after several subsequent glances — the controls seem to be laid out in a counter-intuitive fashion. The filter is placed at the panel's bottom right, while the envelopes are to be found in the top left-hand corner. Similarly, the LFOs are at top right, leaving the bottom left-hand corner for the two oscillators. I don't want to make too much of this design choice — it's a personal thing, after all — but it felt like an unnecessary shuffle-round, to me.

At the back, there's a socket for the external power supply, an on/off switch, a USB port for connection to your computer, MIDI In, Out/Thru and Poly Chain ports, quarter-inch sustain and pedal/CV sockets, and, also on quarter-inch jack sockets, stereo and headphone outputs.At least the pitch and modulation wheels are where you'd expect them to be, raised onto the control panel and shunted over a bit. This keeps the width to the absolute minimum that three and half octaves of full-sized keys can occupy. I'm sure there are some who'd have loved yet another five-octave keyboard and others who'd sigh because even that wasn't enough. For me, the Mopho X4's is the perfect length. Its velocity and channel aftertouch are welcome and the keyboard action is light and fast. With transposition, the range exceeds seven octaves, from F0 up to C8. As a further boost to its controller credentials, the knobs are configurable to transmit either MIDI CCs (Continuous Controllers) or NRPNs (Non Registered Parameter Numbers). The Mopho X4 could, therefore, serve as a hardware front-end for your virtual instruments.

The knobs and encoders are logically mixed, and I think the pairing of selection buttons with encoders is very effective. Cramming four LFOs into such a small space really shouldn't work this well. However, I feel the single set of envelope knobs, with a button to select which of the three should be live for tweaking, is a compromise too far. I was forever prodding the damn button! Otherwise, the Mopho X4 offers instant access to the parameters you'll need most; there are no lengthy menu excursions. The knobs turn without undue wobbling, which is a far cry from those early Prophet 08 encoders.

Continuing across the panel, the LEDs are a refreshing yellow and the synth's less-used 'miscellaneous' parameters are all clearly printed. The black and white display has the regular DSI touch, showing original parameters next to edited values.

Flipping to the rear, we see that the audio outputs are stereo; tasteful panning of the voices can inject a real sense of space. There's a headphone socket, too, and three MIDI ports, although the MIDI Out/Thru requires a software decision — you don't get both. That's because the third five-pin connection is reserved for DSI's Poly Chain mode (which I'll mention again elsewhere). As well as the sustain pedal, there's a second input suitable for a volume or CV pedal. Power comes from a small, light adaptor, leaving the USB port to spurt MIDI at your PC or Mac.

Voice Squad

Rather than recap previous reviews, let's agree that if you've encountered any of Dave Smith's recent analogues, from the Prophet 08 to the Mopho and Tetra, you'll know what to expect from the Mopho X4. At the heart of each voice is a modern variation on the Curtis CEM3396 'synth on a chip', with extras such as sub-oscillators and digital noise slipped in. If you think you've already heard every sound this chip can make, the four factory banks may come as a pleasant surprise. The standard of the patches is high throughout and there's no evidence of padding, except where you'd want it (pads, for example).

Probably the biggest question concerns whether four voices are enough, or, perhaps, whether polyphony matters that much anyway? Certainly, when all voices are stacked together in unison mode, this is a beast to be reckoned with, and there are varying degrees of unison detune available, from the subtle to the downright jarring. In the end, the answer, as always, depends on your personal preference. I'd say four voices can work out just fine unless you're prone to bouts of Rachmaninov. I recently had the chance to play an eight-voice poly-chained setup, when visiting composer Paul Lawler at his studio, and I won't deny that a combined Mopho X4 and Tetra can deliver pads, strings and other long-release patches that are beautifully, doubly lush. Even by itself, splash on a bit of reverb and delay and the Mopho X4 dispels any fears that DCO-based synths must be stale and lifeless. Incidentally, patches can be saved in formats suitable for loading into other DSI synths, which is a further incentive to mix and match.

In Use

The Mopho X4's front panel is deceptively simple and also leaves space for you to park a Tetra on top.

In addition to the four factory sound banks, an equal number of user banks are provided, pre-filled with copies of the presets. This should nudge even the most cautious synthesist to start overwriting and personalising. With eight banks in total, you've got over 1000 patches (!) at your disposal, and I found plenty I'd reach for with no qualms. From such a varied resource it's almost impossible to pick favourites, but I'll venture one anyway: 'Lullaby Repeater', a sublime, hypnotic, decaying electro-harpsichord patch, aided in my case by hanging notes contributed by Logic. Add a liberal dose of effects and you've a recipe for a whole afternoon in the studio.

From kick-ass synth brass to the unsettled burblings of alien digestive tracts, the Mopho X4 has a crack at the lot. There are countless (at least I didn't count them) solo patches of the in-your-face and searing type, and rather fewer of the flowery, new age sort. Pads and strings are lush and tasty, and as for bass, those sub-oscillators could add rumbling nuances to any track. Scrolling through the many hundreds of patches, a few signature timbres recur, one of which is the highly resonant squeal of the 24dB filter. In 12dB mode, the filter becomes more reserved, its resonance toned down. Perhaps I'm showing my age, but I found it the nicer of the two.

Auto-performance fans will relish the arpeggiator and gated sequencer, the former bristling with all the usual up, down, random, and 'as played' modes. Even before grappling with the sequencer you can indulge in pulsing Donna Summer bass lines like it was 1977. Holding the arpeggiator button for a moment latches its operation, and there are two different latch types to choose from. In the first, played notes are latched, but when you release the keys, then add more, the new notes are merged with the originals. In the second mode, 'Relatch', newly-played notes replace all those previously held. This is less easy to explain than it is to use and, fortunately, it occurs without missing a beat.

There's no equivalent way of latching the gated sequencer, though. This requires a sustain pedal or the fixed note trigger of the Push It! button. A button triggering a single note makes sense in the context of a module but feels redundant on a keyboard. It could be better employed by sequencer and arpeggiator alike if it were more configurable. Latching issues aside, the sequencer is fabulous; four rows of parameter shifts, each row with a variable length of up to 16 steps. The sequencer is stepped either at the internal tempo, via MIDI clock, or by playing notes on the keyboard.

When concentrating on the sequencer, I felt the interface was at its least friendly. If you expect to do lots of sequencing, or intend to fully explore the labyrinthine modulation paths, there's no substitute for rodent grappling.

An X4 patch in all its glory in the free LE patch editor software.

Mopho By Mouse

When you're in a programming mood, why labour over multi-functional hardware when there's a free editor available for download? This is the Mopho X4 LE, eager to expose every acre of a synth that, when laid out on-screen, suddenly looks quite imposing. There's a Pro version of the software too, and a VST/AU plug-in version, with RTAS planned soon, but if all you require is visibility of your patches and full access to everything, the LE version is ideal. It communicates as easily as connecting a USB cable, and throughout the review period it performed admirably. I noticed that some of the factory patch names didn't correspond to those in the synth, though, so some kind of bank refresh process would be very welcome.

The Pro and plug-in versions contain further patch name inconsistencies, something the editor's developers, Soundtower, are now aware of, but I had a more significant problem when I turned to the plug-in. After a short period of testing the Audio Unit version in 64-bit Logic, I realised that it doesn't send the correct patch information to the Mopho X4 when a song loads. Once you realise this and transmit the patch manually, there's still another fence left to jump, but this one's even higher! The plug-in adds considerable latency to the track, making it somewhere between hard and impossible to play the Mopho X4 alongside other plug-ins. Soundtower are aware of this and working on it.

I have fond memories of early Soundtower editors for Waldorf synths, in particular the function that generated patches from existing banks using genetics and mutation. This laboratory-style spawning of new sounds is beautifully realised and could be worth the price of the Pro version of the software alone. Demo versions are offered, so you can check the functionality out for yourself with your DAW of choice. Frankly, you'd be a crazy mofo not to.


With the passage of time, I came to appreciate the Mopho X4 more and more, as much for its form factor as for its collection of giggable, tweakable sounds. Full marks to Dave Smith for prioritising portability — we may just have hit the optimum size-to-fun ratio!

Four voices played from a keyboard this length feels right to me, but there's also that other whispering voice: the one in my head saying that the count can be doubled by buying a Tetra. Maybe this vision of expansion eventually becomes irresistible, but at around a thousand pounds$1300 to get started, the Mopho X4 isn't cheap. For that much, I'd have hoped for two sets of envelope controls, at least! That aside, this is a solid, punchy and fine-sounding synth that can handle a wide variety of analogue roles.

The Mopho X4 doesn't surprise, startle or subvert. It's a repackaging job certainly, but that's a simple statement of fact, not a put-down. Who could have predicted, 10 or 15 years ago, that we'd be seeing a succession of four-voice analogues when virtual analogues of the day promised five times the voice count, effects, half a dozen filters and a free foot-rub? Dave Smith has made a large contribution to analogue's new wave, which shows no signs of abating, and even if the Mopho X4 represents the last drop squeezed from one ultra-versatile chip, it's still a winner. Which is what counts.  


If you're in the market for a self-contained analogue polysynth, the only serious competition right now comes from further up Dave Smith's range, in the form of the Prophet 08. There are also various Mopho/Tetra combinations that let you grow in affordable stages. If you don't mind an external keyboard and are willing to trade programmability for accessibility, Vermona's Perfourmer Mk2 is a classy-sounding four-channel instrument.


  • It's a modern, portable, knobby, polyphonic analogue synth with keys!
  • Sounds great.
  • Extensive library of factory sounds plus over 500 user memories.
  • Free editing software.


  • The controls are oddly laid-out and not all the multifunctionality is painless.
  • No latch for the sequencer.


Once again, Dave Smith puts four Mophos in a box, but this time he doesn't Tetrafy them. Reduced to the minimum dimensions a polysynth could be, the Mopho X4 is a bigger analogue synthesizer than it seems.



Dave Smith Instruments +1 707 963 7006.


Dave Smith Instruments +1 707 963 7006.