Premier Guitar features affiliate links to help support our content. We may earn a commission on any affiliated purchases.

MXR Custom Shop Sub Machine Octave Fuzz Review

Hip and nasty fuzz flavors and octave tones from both sides of the EQ spectrum.

Octave fuzz often walks a fine line between ecstatically unbridled and a bit trashy. For every Jimi Hendrix or Pete Townshend solo driven to screaming high-octave heights or tasty “Fool in the Rain” Blue Box flurry, there’s some jerk playing a boneheaded riff for a beer commercial that makes you feel like you need a shower and a week at a silent Zen retreat.

What’s fun about MXR’s Sub Machine octave fuzz is that it offers a path to both extremes. And thanks to a well-executed, sensitive control set and independent octave-up and sub-octave voices, you can navigate the sometimes nebulous no-man’s land between sublime and stupidly scuzzy—and even uncover some pretty classy tones along the way.

The basic fuzz voice is killer—particularly if you dig buzzing mid-’60s to early-’70s fuzz with a silicon edge.

Built Like a Brute
The mechanical heart of the Sub Machine is MXR’s La Machine fuzz—the company’s homage to the unsung but awesome Foxx Tone Machine. All the functionality of the La Machine is here in the form of volume, tone, and fuzz knobs. And the octave switch is vastly improved from the original La Machine simply by making it a footswitch rather than a minuscule button.

The fourth knob in the set is for the sub-octave volume, which can be dialed back to zero octave content or up to Jabba the Hutt levels of corpulence. (It can even be used alone when the fuzz volume is off, so you can double as a bass player in a pinch.) The fifth control is a very cool series/parallel switch that runs the sub-octave and fuzz/high-octave signals independently until they are summed at the output. In series mode, the sub-octave signal is fed into the fuzz circuit, which can lend both delicious chaos and control to the proceedings.

Powerfully Purple Acid Rain
Any fears that the Sub Machine dwells too permanently in the aforementioned “trashy” side of the octave fuzz spectrum are easily quelled by exploring its simplest and most subdued voices. For starters the basic fuzz voice is killer—particularly if you dig buzzing mid-’60s to early-’70s fuzz with a silicon edge. One of my favorite things about the Sub Machine’s fuzz circuit is how buzzing, full, and sustaining it can sound at low pedal, amp, and guitar volume levels when you crank the fuzz.


Surprisingly versatile and full of tone-shaping possibilities. Good value. Killer basic fuzz voice.

Sub-octave voice can sound woofy and artificial at high levels.


Ease of Use:




MXR Custom Shop Sub Machine

That said, it’s happiest and most at home when it’s wide open and roaring. While it’s not the most dynamic fuzz and won’t be everyone’s cup of tea, I love its raunchy, acerbic personality and mod-meets-airbrushed-custom-van mixture of Big Muff brawn and lacerating Fuzzrite and Tone Bender buzz. The octave-up voice is the icing on the cake: It adds hints of hair-singeing Octavia and Superfuzz octave tones, but with what often sounds like a touch more sustain and breadth.

As with most octave-down guitar devices, the Sub Machine’s sub-octave effect is one you’ll either love or hate. To some, the rotund, synthy, and harmonically compact tone signature is funky beyond measure. Those who savor the most colorful and overtone rich bass content possible will hear it as artificial and skanky. (If you’ve been following, this is where the trashy part of the equation factors in.) The artificiality of the sub-octave is most prominent when you run it in parallel. In fact, it can get queasily gut rumbling if you’re running the pedal through a powerful amp with high-wattage speakers. But there are enough soft contours in the sub-octave tone and range in the sub volume control that you can make it a very seamless part of the fuzz voice at lower sub volumes.

You can more musically enmesh the fuzz and sub by running the two in series. At low sub levels, the sub-octave can become a cool baritone undertow. At higher ones, it adds a nasty glitchiness that Jack White fans will relish. Yet the real takeaway is that there are surprisingly numerous ways to make these two effects work together, and many of the least obvious and most subdued amalgams of the two often produce the coolest results.

The Verdict
Obscene as the Sub Machine can be, it is ultimately a very clever and imaginative bit of fuzz design that’s musical in applications way beyond filthy caveman riffage. While MXR has built similar pedals—most notably in the form of the Slash Octave Fuzz—the Sub Machine brings a sassier, classier, and more ’60s-tinted fuzz voice to the mix. For anyone willing to dig deep into the tone shaping potential of this potent purple machine, a world of sonic surprises awaits.

Watch the Review Demo: