The Mopho x4 is a four-voice analog polysynth keyboard introduced by Dave Smith Instruments in August 2012. Built on the same core voice architecture as the earlier Mopho and Mopho Keyboard, it translated that engine from a compact monophonic instrument into a portable 44-key chord-capable synth with aftertouch, a deeper performance interface, and the same emphasis on punch, sequencing, and modulation. Its significance lies less in luxury than in access: it brought a distinctly DSI-style analog sound into a smaller, more affordable, self-contained polyphonic format.
Sound and character
In practice, the Mopho x4 sounds assertive, bright, and muscular rather than silky or overtly nostalgic. Contemporary reviews repeatedly described it as “powerful and punchy,” and that assessment makes sense when you look at the design: two oscillators per voice, two sub-octave generators per voice, a Curtis low-pass filter, and a programmable feedback loop make it especially strong at basses, aggressive leads, sync sounds, metallic edges, and animated sequences.
What makes the instrument memorable is that it does not really try to flatter everything equally. The Mopho x4 can do pads, but reviewers noted that lush, soft, rounded pad work is not where it sounds most naturally at home; its DCO/filter combination and overall voicing tend to project a forward, cutting, slightly hard-edged identity. That is not a flaw so much as a personality. It behaves like a small poly that still thinks like a performance-minded Mopho: energetic, direct, and more interested in tension than pastel smoothness.
Features and architecture
- Manufacturer: Dave Smith Instruments; the product is now archived and supported on Sequential’s legacy site.
- Year: 2012, with launch coverage and shipping beginning in August 2012.
- Production years: Introduced in 2012 and now discontinued / out of production.
- Synthesis type: Analog subtractive synthesis with a 100% analog signal path.
- Category: Compact polyphonic analog keyboard synthesizer.
- Polyphony: 4 voices.
- Original price and current market price: It shipped at US$1,299. As of March 2026, Reverb shows an estimated value range of about C$745–C$1,065 for Good-to-Mint examples, with active used listings around US$849–US$1,170 and occasional higher mint / new-old-stock asks.
- Oscillators: 2 oscillators per voice, plus 2 sub-octave generators per voice, with hard sync.
- Filter: 1 Curtis low-pass filter per voice, switchable between 2-pole and 4-pole operation; self-oscillates in 4-pole mode.
- LFOs: 4 LFOs per voice.
- Envelopes: 3 envelope generators per voice, ADSR plus delay.
- Modulation system: 20 modulation sources and almost 50 destinations, plus audio-rate filter modulation and a programmable feedback loop.
- Sequencer / arpeggiator: Gated 16 x 4 step sequencer per voice, one sequence per program, plus arpeggiator.
- Effects: No dedicated onboard effects section in the modern delay/reverb sense; instead, it uses a feedback loop to add thickness, saturation, and more abrasive harmonic content.
- Memory: 1,024 programs total: 4 banks of 128 factory presets and 4 banks of 128 user programs.
- Keyboard: 44-note, full-size, semi-weighted keyboard with velocity and aftertouch.
- Inputs / outputs: Stereo 1/4-inch unbalanced outputs, headphone out, sustain pedal input, and expression pedal / control-voltage input.
- MIDI / USB: MIDI In, Out/Thru, Poly Chain, and USB type-B.
- Display: Small two-line LCD display.
- Dimensions / weight: Approximately 25.2” x 11.1” x 3.6”; 13.5 lbs.
- Power: External 15V supply, with included PSU for 100V–240V AC operation.
Strengths
- A genuinely distinctive small-poly voice. The sub oscillators, Curtis filter, and feedback path give the Mopho x4 more low-end push and edge than a generic “entry analog poly” label suggests. It does not disappear in a mix.
- Deep modulation for its class and price. Four LFOs per voice, three envelopes, a flexible modulation matrix, and the step sequencer make it far more than a basic preset machine; it rewards programming.
- Compact but still performance-capable. The 44-note semi-weighted keybed, velocity, and aftertouch gave players a more serious live instrument than many compact analog competitors of the period.
- Front-panel editability without full menu exile. DSI explicitly positioned it as fully programmable from the front panel, and reviewers generally agreed it was practical to navigate even if not truly knob-per-function.
- A lower-cost route into the Prophet/Mopho family sound. Reviewers repeatedly framed it as a more affordable way into the same broader DSI tonal universe occupied by instruments like the Prophet ’08.
Limitations
- Only four voices. For many parts that is enough, but dense chords, sustained pads, and split-handed playing can expose the limit quickly.
- Monotimbral architecture. It cannot layer, split, or function as multiple separate mono parts the way a Tetra-based workflow could, and that significantly shapes how “big” the instrument feels in use.
- No audio input on the x4. The earlier Mopho Keyboard had external audio input; reviewers specifically noted that the x4 lost it, which removes one of the more experimental aspects of the Mopho concept.
- Pads are possible, but not its most naturally flattering territory. The x4 can sound broad and impressive, yet warm, smooth pad work generally takes more effort than on softer-voiced polysynths.
- Partially shared controls. The envelope section still relies on selecting which envelope you are editing, which is workable but less immediate than a fuller knob-per-function panel.
Historical context
The Mopho x4 arrived in August 2012, at a moment when interest in analog hardware was rising fast but the field of affordable, programmable analog polysynths with keys was still relatively narrow. Dave Smith Instruments had already established the Mopho as a strong, characterful mono line and the Prophet ’08 as a more expansive modern poly; the x4 sat between those poles. It effectively asked a focused question: what happens if the Mopho becomes chordal without becoming a flagship?
That timing mattered. Reviewers immediately understood the instrument not as a luxury statement, but as a strategic middle option: cheaper than the Prophet ’08, more self-contained than a desktop-plus-controller setup, and more playable than the original Mopho formats. MusicRadar went so far as to call it the only analogue four-voice keyboard-equipped poly with aftertouch under the sub-£1,000 mark at the time, which helps explain why the x4 felt important even without headline-grabbing spec excess.
Legacy and significance
The Mopho x4 matters because it broadened what the Mopho identity could mean. Before it, “Mopho” largely implied a compact, edgy mono instrument with a lot of attitude. The x4 preserved that edge but made harmony central, turning a voice architecture associated with basses, sequences, and wiry leads into something capable of full chordal playing and live performance without abandoning its bite.
Its deeper significance is that it helped normalize the idea of the compact analog performance poly as a serious instrument rather than a compromise. In retrospect, that feels historically meaningful: not because the x4 dominated the market, but because it showed that a smaller, tougher, more affordable analog poly could have a clear artistic identity of its own instead of being merely a cut-down flagship. It was one of the instruments that made the 2010s analog resurgence feel practical, not just aspirational.
Artists, users, and curiosities
The most directly documented user association comes from Jason Lindner, who told Sequential that the Mopho x4 became his road synth and later his local gig synth, and that he programmed sounds on it before moving them back into his Prophet ’08 workflow. That detail is revealing: it suggests the x4 was not only a cheaper DSI keyboard, but a legitimate creative workstation inside a professional rig. Lindner also said he used the Mopho x4 among the DSI instruments he programmed during the sessions connected to David Bowie’s Blackstar era, which gives the instrument a real, if understated, cultural footprint beyond gear-demo circles.
There is also a clear electronic-pop connection. In a 2016 MusicRadar interview, Jon George of RÜFÜS identified “the x4” as part of the group’s hardware synth setup during the period around Bloom. That matters because it places the Mopho x4 not only in jazz-adjacent experimental contexts, but also in contemporary touring and production environments where immediacy, recall, and mix-cutting tone matter.
A useful curiosity is that, from the start, the Mopho x4 was often mentally compared to a “Tetra with keys,” but DSI-era coverage and reviews insisted that this was the wrong way to understand it. The x4 was monotimbral, lacked split/stack/multi modes, and even dropped the audio input found on the Mopho Keyboard. In other words, its identity was narrower than a Tetra-based fantasy version would have been, but also sharper: it was a polyphonic Mopho, not a mini workstation. That distinction is one reason it still feels so specific.
Market value
- Current market position: The Mopho x4 sits as a respected discontinued DSI-era compact poly rather than as a top-tier collectible. It is valued for sound and character more than for rarity theater.
- New price signal: Truly new or effectively new old stock examples do appear, but sporadically, and asking prices can climb well above typical used-market levels.
- Used market signal: The used market is active enough to establish a real floor and range; recent examples and guides cluster roughly from the mid-hundreds into the low-thousands, depending on condition and seller ambition.
- Availability: It is discontinued, but still not especially hard to locate through major used platforms. Finding one is much easier than finding a rare vintage poly, though condition and region can swing pricing noticeably.
- Buyer notes: The main value question is not whether the instrument is famous, but whether you specifically want this sharper DSI/Mopho voice in a compact keyboard. Buyers should pay attention to condition, included PSU, and general legacy-synth upkeep rather than assume every listing is equivalent.
- Support ecosystem: Support is stronger than many discontinued synths: Sequential still hosts the product page, manual, factory sounds, and OS download, and it links to editor resources and replacement accessories.
- Long-term position: The Mopho x4 looks less like a speculative collectible and more like an underrated specialist: a compact, aggressive, modulation-rich analog poly whose long-term appeal depends on whether players want its bite rather than generic “warmth.”
Conclusion
The Mopho x4 represents a very specific and still compelling idea: a compact analog polysynth that favors punch, immediacy, modulation depth, and stage practicality over prestige and excess. It was never the smoothest or most luxurious keyboard in Dave Smith Instruments’ lineup, but that is exactly why it remains interesting. The Mopho x4 matters because it did not dilute the Mopho concept when it became polyphonic; it made that concept playable in chords and proved that a smaller modern analog poly could still have a fierce, unmistakable identity.