DSI Mopho X4

Dave Smith’s synths are so consistently great, we here at ProAudioStar have taken to calling him Uncle Dave. Well, fellow synth-heads, this time Uncle Dave did more than buy us a ginger ale and drive us to Tee-ball. The X4 captures a coveted corner of the synth market – the affordable polyphonic analog corner. After playing with this puppy, we were wowed by it’s warmth and style.

This completely analog four-voice synth basically takes four Mophos (DSI’s acclaimed monophonic synth) and stacks them together with even more features to help you customize patches.


In our tests the X4 often sounded akin to the Prophet ’08. It has that fat analog bass sound, but it’s filters allow for plenty of high-frequency response too. . The X4 also features the famous Curtis four pole low pass filter. Overall the X4’s is more tonally capable of noticeable textures that sometimes lean gritty or sharp, than more nuanced supportive-type pads. So if you’re looking for smoother patches, you’ll usually have to do some patch editing.

Thankfully, editing patches is a breeze due to the X4’s sensible layout and the downloadable patch editor, which can load custom patches to the unit via USB.

The X4 has two digitally controlled oscillators and four low frequency oscillators per voice, plus a feedback circuit for extra oomph, as well as three envelope generators. This signal path is 100% analog, but is controlled digitally, giving you the best of both worlds (a feature we think will become more and more common in the realm of analog synths). The addition of two sub-oscillators provided superbly exciting depth to many of the lead and bass patches we tested.

I had a blast messing with the sequencer for sequenced chords, and the arpeggiator, both sync-able via the tap tempo “Push It!” button or MIDI clock in. The Push It! Button can be programmed to trigger custom functions, leading to some very cool possibilities.

While the X4 is not multitimbral, it is designed to work with a DSI Tetra synth-module, which expands the total number of voices to eight in total. There’s a satisfyingly perfect spot on the right-hand side of the X4’s surface for the Tetra to sit, should you use them together. Coincidentally, most of the Eventide pedals also fit perfectly there. We got some amazing sounds running the X4 through the Eventide Space pedal – a highly recommended combo that helped us to expand and further texturize some of the X4’s tones.


The X4’s build is great. It has a velocity-sensitive keybed with responsive aftertouch that allow for nuanced playing. It features hard-platsic knobs and wheels, a matte black aluminum body and wood side-panels. The 44-key keyboard is an ideal size- big enough for a wide tonal range but still small enough to take to gigs.

The X4 features stereo and headphones out, CV and sustain in, MIDI In and Out/Thru plus MIDI poly chain for DSI synths, as well as USB.

The Nicest Mopho Around

Overall, the X4 offers the classic DSI sound, made famous by the Prophet series, at a more affordable price and portable size. At 44 keys, banks on banks on banks of strong analog sounds, and the ability to easily customize patches, it’s no wonder that at $1,299 the Mopho X4 has been a very popular synth at ProAudioStar. We dig it, and we think you will too.

The DSI Mopho X4 is available now for only $1,299.00 from your favorite synth dealers, ProAudioStar.

– Clay