MXR Slash Octave Fuzz

The MXR Slash Octave Fuzz SF01 is a signature fuzz pedal from MXR, developed with Slash and first shown in May 2012¹²³. It packs three voices into one analog box: a main '70s-style fuzz, a sub octave an octave below what you play, and an octave-up fuzz, which MXR describes as a way of "thickening up your tone with a sinister growl"³⁴. Vintage Guitar called it three fuzz "flavors", Sub-Octave, Fuzz, and Octave Up, offering "a palette of distinctive, utilizable sounds"¹.

The pedal came out of a direct collaboration. Slash explained the process at launch:

Vintage Guitar reported that Slash provided input to the Dunlop design team while they tweaked prototypes, and that the pedal can be heard on his album Apocalyptic Love¹.

Three voices: sub octave, fuzz and octave up

The SF01 is really three effects in one enclosure, and its strength is that you can use them individually or stacked. The Sub Octave voice can be run dry or switched into the '70s-style "shag" fuzz circuit⁴³. The main fuzz is what MXR calls "thick '70s shag"³, and the Octave Up Fuzz adds what the manual calls "Psychedelic Octave Up fuzz"³ with a chainsaw grind on top³.

MusicRadar's reviewer, Simon Bradley, found the main fuzz "sounds more Fuzz Face than Big Muff Pi"², and that with the sub and high octaves balanced against the fuzz "you'll have a colossal sonic bombardment of three-octave artillery at your disposal"². Guitar World's reviewer found the pedal "shines when used to thicken the signal and create a wider soundstage of pitch and depth variations"⁸.

Vintage Guitar's verdict on the architecture:

Controls and footswitches

There are two footswitches. The left one (On) engages the pedal, while the right one (Up) engages the octave-up fuzz in addition to whatever mode you have configured⁹. A mini top-panel button, Sub Into Fuzz, activates the main fuzz²⁸.

The Volume knob's dual behavior is worth understanding: with Sub Into Fuzz disengaged it controls your dry level, and with it engaged it controls the amount of main fuzz⁹⁷. If Sub Into Fuzz is not on, you get no fuzz on the main note at all².

The pedal can also be run as a standalone fuzz: activate the left switch with the mini top-panel button engaged and turn down the suboctave knob⁸. Vintage Guitar highlighted the flip side, the ability to bypass the fuzz entirely and "deliver a different sort of overdrive or distortion along with a sub-octave effect"¹.

Internal trim pots and sample settings

Inside the pedal are two trim pots for the octave-up circuit: a GAIN trim pot that controls the intensity of the Octave Up fuzz, and a TONE trim pot that shapes the overall EQ⁷². These are internal controls, so shaping the octave-up voice means opening the box¹⁰.

The manual also includes three sample settings, named SLASH 1, SLASH 2 and SLASH 3, covering both octaves, octave up alone, and sub octave alone⁷. They give a starting point for each of the pedal's main configurations.

Power and connections

Setup is conventional: run a cable from your guitar to the INPUT jack and another from the OUTPUT jack to your amplifier⁷. Power comes from a 9-volt battery, a Dunlop ECB003 9-volt adapter, or the DC Brick, Iso-Brick and Mini Iso-Brick power supplies, none of which are included³. Current draw is 17 mA⁷, light enough that battery power is practical.

Other manual specifications: fuzz gain range of 40 dB, octave up gain range of 20 dB, sub octave corner frequency of 149 Hz, dry max gain of +1.6 dB, and signal to noise greater than 85 dB with all controls at mid position, A-weighted⁷.

Designed with Slash, from the Blue Box and Octavia

The SF01 has a clear circuit lineage. Vintage Guitar reported that one of Dunlop's goals was "to develop a more-predictable version of the '70s MXR Blue Box fuzz pedal, and the Slash achieves that"¹⁹. The original Blue Box was an octave/fuzz pedal used by Jimmy Page on Led Zeppelin's "Fool In The Rain"¹². Premier Guitar placed the Slash Octave Fuzz "closest in spirit to, say, a Fuzz Face and Octavia in tandem", noting it pays homage to the Tycobrahe Octavia and Boss OC-3 Super Octave, and that the silicon-based circuit is voiced with plenty of brash midrange boost, which is how Slash tends to set his own EQs¹³.

Vintage Guitar noted that few listeners associate Slash with octave fuzz, but that he uses it on occasion to color his sound rather than overpower it¹. The enclosure carries his identity plainly: a heavy-duty housing with custom artwork featuring Slash's tophatted-skull-and-crossbones motif¹, in a distressed finish matching the Dunlop SC95 Slash Cry Baby Classic wah released alongside it²⁸.

What reviewers said

Published reviews were broadly positive about the concept and the build, with one consistent caveat about tracking.

• Premier Guitar: "Sub octave and octave up circuits offer many tone options. Built for the road. Voiced for searing, shaggy fuzz."¹³
• MusicRadar (Simon Bradley): "The SF01 is best suited to single notes; chords tend to present a few grim glitches, though lo-fi junkies will probably love that!"²
• MusicRadar also found "Hendrix-style tones are faithfully recreated, but it's when the sub and high octaves are used with the fuzz that the walls begin to crumble."²
• Guitar World: the pedal "shines when used to thicken the signal and create a wider soundstage of pitch and depth variations"⁸.

The chord-tracking point matters if you are comparing this against a modern polyphonic octave and pitch pedal: the SF01 is an analog, monophonic-minded design, and its glitches are part of that character. Players wanting the Blue Box idea with polyphonic tracking and more control can also look at the later MXR M306 Poly Blue, which expanded the concept with four octaves, modulation and a switchable fuzz circuit.

For fuzz alone, MXR's range includes the Classic 108 Fuzz and the Hybrid Fuzz, but the SF01 remains the one that stacks sub octave, fuzz and octave up in a single analog signal path, tuned to Slash's taste.

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