When it comes to modern analog synths with a pedigree, the
trinity of Dave Smith, Moog, and Tom Oberheim have led the way for the
better part of a decade now. Each has their sound and strengths, so
saying that one is “better” than the others is like saying that
chocolate is better than bacon—I can’t survive without either. In
addition to my collection of vintage gear, I’ve had a Prophet ’08 since
its introduction, and the Mopho-based products have made appearances in
my studio as well, so I’m intimate with the sound. Naturally, when the
Mopho x4 was announced, I was all over it, so here are my thoughts.
Unboxing the Mopho x4, I was struck by how compact it is.
Part of this comes from the fact that the pitch and mod wheels are on
the front panel as opposed to the end of the keyboard, but that
presented me with no problems soloing. Despite its size, the
construction of the x4 inspires confidence. Its charcoal metal casing
feels like a tank, and the retro wood end panels seem quite hardy. The
velocity- and aftertouch-sensitive keyboard feels identical to the
The front panel layout is the same as the original Mopho,
which means many of the knobs have multiple functions. For example, the
two oscillators share identical functions, so there’s one set of knobs
for both and users toggle between oscillators via a dedicated button.
There’s a similar approach with three of the four envelopes. While I
prefer a one-function-per-knob approach, the overall design of the x4
panel is sensible and quick to master.
Flipping the x4 around, the back panel is surprisingly
uncluttered. In addition to both USB and five-pin MIDI, there are stereo
outs, sustain and expression pedal inputs, a headphone out (with lots
of headroom, I might add) and Dave Smith’s Poly Chain MIDI connector,
which lets you add other Dave Smith synths, including the Tetra,
original Mopho, Mopho Keyboard, and even the Prophet ’08, for up to 16
voices of polyphony. (With identical sound programs loaded into each
one, the master keyboard sees the whole kit and caboodle as one giant
synth. Note that the Prophet lacks the Mopho line’s sub-oscillators and
feedback, so you’ll want to avoid patches that require those if
poly-chaining.) I’d like to see an input for processing external audio
like on the Mopho desktop module, but implementing that on a polyphonic
synth can be a little tricky compared to a monosynth.
Since they’re based on the Mopho, the x4’s oscillators are actually more
flexible than those found on the Prophet ’08. In addition to sawtooth,
triangle, saw/triangle hybrid, and fully adjustable pulse waves, the
x4’s oscillators also include sub-oscillators for each. These generate
additional square waves—either one or two octaves below oscillators 1
and 2. As a result, the x4 can deliver massive textures, especially when
the main oscillators are set to octaves or fifths at higher registers.
The oscillators can also be hard synced, which is great
for those vintage squawky leads made popular by the Cars, and that my
colleague Jerry Kovarsky has been studying in the past three issues’
“Art of Synth Soloing” columns. Hard sync is also super-useful for
morphing and evolving riffs, especially when paired with the X4’s
A noise generator, located in the mixer section, works
wonders for pumping up techno and electro leads. Also in the mixer
section is a feedback knob, which does that nifty old-school trick of
routing the synth output back into the filter. At low settings, it’s a
great way to add grunge and dirt to your sounds. At high settings, with a
touch of detuning in the oscillators? Full-on audio mayhem.
The filters on the x4 are based on the legendary Curtis
chip and are identical to those on the Prophet and Mopho, so they sound
freakin’ awesome. The roll-off slope can be switched between a bright
and lively two-pole (12dB-per-octave) and a subjectively warmer
four-pole (24dB-per-octave) mode, the later of which can self-oscillate.
If you’re going for that classic Oberheim brass sound, two-pole is the
way to go. For darker ambient pads and screaming resonance, four-pole is
What’s more, there’s an audio mod option that lets you use
oscillator 1 as an FM modulator for the cutoff frequency. Boost the
resonance into self-oscillation and this knob expands the x4’s palette
into metallic and bell-like sounds as well as sideband-heavy insanity.
The rest of the filter implementation is straightforward
stuff: cutoff, resonance, keyboard tracking, and bipolar envelope
amount. Can’t argue with classic, right?
Four LFOs, four step sequencers, and slew of matrix
modulation options deliver an embarrassment of riches in this
department. The x4’s two-line LCD keeps you informed of what goes where
if you start getting lost in the knobs and switches.
The four LFOs are identical to those on the Prophet ’08:
five waveforms (including random), tempo sync via MIDI, key sync (for
restarting the LFO every time you hit a key), and the ability to route
the LFO to virtually any parameter in the x4, which is saying a lot when
you start doing magic tricks with hard sync, resonance, and feedback
One of the hallmarks of Dave Smith’s modern designs is the
inclusion of four step sequencers in almost every product. These aren’t
simple note-only affairs. Like the LFOs, you can assign them to an
astonishing range of synth parameters. Quite a few factory presets make
great use of these tools, notably “MetalNoizLoop” and “SteppingStone.”
Sequences can be up to 16 steps and support odd lengths, so you’re not
trapped in an eight- or 16-step world.
As if that weren’t enough, the x4’s can route the LFOs and
sequencers to additional destinations, as well as serving as the nerve
center for MIDI controllers like the mod wheel, velocity, and
With so many modulation possibilities, it’s easy to get lost in the details as you tweak your sounds. Fortunately, Soundtower.com
has an x4 software editor that delivers a lot of visual clarity, like
their other editors for the Prophet, Mopho module, and Tetra. If you’re
not going too deep with your own sound design, and instead tweaking with
an eye to live performance, you can easily handle it all from the front
To put the Mopho x4 through its paces, I made it sit in
for my Prophet ’08 for two weeks. During that time, I discovered that
the Mopho sounded considerably more aggressive than the Prophet, thanks
to the dual sub-oscillators and feedback knob.
On the other hand, I never really felt the same intuitive
connection that I have with the Prophet ’08, thanks to its plethora of
single-function knobs and switches. On a Prophet, I can whip up an
entirely new sound with sequences and complex LFO routings within a
matter of minutes. With the x4, things go a tad slower because of all
the toggling, which for most players won’t be a deal-breaker, because
essentials like cutoff, resonance, and envelopes are right there.
In a track, the x4 slides right into place and does a
fantastic job at everything from silky pads to nasty, in-your-face
leads. One of my Facebook fans commented that it’s more of a “band”
keyboard than a dance music tool, and while I’d gladly use it as my main
lead synth in a band context, I also had zero trouble coming up with
EDM sounds of all kinds and strongly recommend the x4 to any electronic
producer looking for a true polyphonic analog synth.
That said, I was disappointed that Dave Smith didn’t
include the Tetra’s multitimbral mode as a performance option, as it
would have been a great way to add even more value to a feature-packed
synth. Maybe in a software update?
You could say that the Mopho x4 is like half a Prophet ’08
for half the price, but that would miss the point. The Mopho
architecture has a different sound. It’s way more aggressive in some
ways and maybe a little leaner in others, but still light years better
than any software emulation you’ll find in today’s market—and unlike
much of the competition in the hardware realm, it’s polyphonic. The
simple fact is this is the most cost-effective and sonically flexible
analog polysynth on the market today. Here’s to another slam-dunk from a
Fully analog signal path. Curtis-based lowpass filters.
Dual-sub oscillators, filter FM, feedback and hard sync deliver
aggressive sonics and a boatload of flexibility. Keyboard senses
Programming the step sequencers is a tad fiddly from the front panel alone. Not multitimbral like Dave’s four-voice Tetra.
Want real analog? Need polyphony? The Mopho x4 is the biggest bang for buck of anything out there.
$1,429 list | $1,299 street