ZVEX Mastotron: The Fuzz Pedal That Put a Volume Knob on Your Pickups

Most fuzz pedals ask you one question: how much? The ZVEX Mastotron asks you five, and one of them is a question almost no other stompbox in the world has ever bothered to ask out loud. It wants to know what your guitar’s output impedance is doing to its input stage — and then it hands you a knob to change the answer.

That knob is called Relax/Push, and it is the reason this pedal has spent seventeen years quietly turning up on pedalboards belonging to people who could afford absolutely anything. Annie Clark. Chris Wolstenholme. Mike Kerr. Matt McJunkins. Cage The Elephant. It is a $179 fuzz box built in Minneapolis by a man best known for hand-painting circuit boards and naming things after mastodons, and it has outlived three generations of boutique fuzz hype by being genuinely, structurally different from everything around it.

This is the story of what the Mastotron actually does, who actually uses it — verified, not laundered from a brand roster — and how to set the thing up so it sounds like a stampede rather than a paper bag full of wasps.

A Housekeeping Note Before We Start

Our source list files the Mastotron as a fuzz pedal. So does ZVEX, whose own site sorts it under Fuzz. So does Premier Guitar, which reviewed it in the fuzz category in 2009. For once, everybody agrees, which after several months of writing these guides feels like an unexpected gift.

The complication is subtler and more interesting: the Mastotron is a guitar fuzz that a very large fraction of its actual owners bought for bass. Premier Guitar’s verdict explicitly recommended it to bassists. ZVEX’s own copy leads with the phrase “sub-heavy.” Three of the five artists ZVEX itself names as Mastotron users are bass players. If you have arrived here expecting a straightforward six-string fuzz article, understand that half the pedal’s design intelligence is pointed at frequencies below where most guitar fuzzes bother to look.

Where the Mastotron Came From: The Vextron Compromise

Zachary Vex started ZVEX Effects in 1995 with a business model that was, by any conventional measure, insane: hand-painted enclosures, hand-built circuits, prices to match, and a product line that included a pedal you controlled by waving your foot near a copper plate. It worked. By the mid-2000s the Fuzz Factory had achieved the rare status of a boutique pedal that non-boutique players knew by name.

Premier Guitar’s Jordan Wagner summarised the company’s early trajectory neatly in his June 2009 review: one of the first three Fuzz Factories went to David Sylvian, two of them can be heard on Semisonic’s “Closing Time,” and Billy Gibbons and Steve Albini picked the pedals up shortly after. The brand spread from there into records by Dinosaur Jr., Nine Inch Nails, Portishead and the Smashing Pumpkins.

The problem with that model is arithmetic. Hand-painting a pedal costs money, and that cost lands on the customer. ZVEX’s answer arrived in two stages. First the Vexter series — same circuits, screen-printed graphics, roughly two-thirds the price. Then, in early 2009, the Vextron series: pedals designed from the ground up at a lower price point, aimed squarely at players who wanted the ZVEX sensibility without the ZVEX invoice.

The Vextron line launched with two pedals. One was the Distortron, a stripped-down Marshall-in-a-box that shared DNA with the ZVEX Box of Rock. The other was the Mastotron. The manual’s own version stamp reads MASTOTRON V1.0, February 2009; Premier Guitar’s joint review of the pair ran on 22 June that year and scored the Mastotron 4.5 out of 5 against the Distortron’s 4.0.

What is worth noticing is which of the two pedals got the better score. The Distortron was the safe one — a proven voice, a proven market. The Mastotron was the weird one. The magazine preferred the weird one, and so, over seventeen years, has the market: the Distortron has long since disappeared from ZVEX’s catalogue, and the Mastotron is still in production at $179, listed in stock on the company’s own store as of this writing.

Specifications

Attribute	Detail
Model	ZVEX Mastotron, Vextron Series
Circuit type	Silicon fuzz
Version / date	V1.0, February 2009 (manual last updated June 2011)
Origin	ZVEX Effects, Minneapolis / St. Louis Park, Minnesota, USA
Knobs	Relax/Push (source impedance), Fuzz, PW (pulse width), Tone, Vol
Switch	Three-position Subs selector, marked 2–1–3
Subs positions	3 = huge; 2 = medium; 1 = “absolutely none left”
PW range	Square wave (counter-clockwise) to narrow pulse (clockwise)
Instruments	Guitar and bass; also rated for keyboards and line-level re-amping
Dimensions (L×W×H)	4.70″ × 2.38″ × 1.82″
Current draw	Approximately 1 mA
Battery	One 9V, mounted on edge in the centre of the enclosure; ships carbon-zinc, alkaline recommended
DC power	9V jack, standard Boss configuration, centre negative, on the side of the pedal
Bypass	Mechanical footswitch with LED indicator
Enclosure access	Four base screws
Warranty	1 year from purchase, or as provided by law (EU/UK)
Current price	$179 direct from ZVEX (in stock)
2009 launch MSRP	$149.99 (per Premier Guitar review)
Typical street / used	Around $159 new, roughly $120 used at the time of writing

The One Millamp Question, and the Price Question

Regular readers of this series will know that we run into a power-spec contradiction on roughly every third pedal we cover. The Mastotron mostly spares us. ZVEX’s manual is unambiguous: current draw is approximately 1 mA, described as “low current operation” that “will give you extraordinarily long battery life.” That is one of the lowest figures we have documented on any dirt pedal in this entire guide — a third of what the Box of Rock draws, and something like a hundredth of what a modern digital reverb wants.

The practical upshot: a Mastotron will run on a battery essentially forever, and it will not stress even the most crowded, most under-specified power supply on your board. If you are the kind of player whose pedalboard brick is permanently one outlet short, this is a pedal you can add without doing any maths.

Two housekeeping details from the manual that people get wrong. The DC jack is standard Boss configuration, centre negative — the ordinary thing, not one of the centre-positive oddities you find on older or European boxes. And ZVEX adds a specific instruction: “Use a high-quality 9V adaptor for all high-gain effects.” Fuzz circuits are ruthless amplifiers of power-supply noise, and this one has enormous gain available. A cheap unregulated wall wart will make a Mastotron hum in a way that a Tube Screamer never would.

Where there is a discrepancy, it is on price rather than power, and it is entirely explicable by seventeen years of inflation. Premier Guitar’s 2009 review listed an MSRP of $149.99. ZVEX’s current store price is $179. Third-party listings at the time of writing cluster around $159 new and $120 used. We mention this only because you will find old forum threads quoting the 2009 number as though it were current; it is not, and a $149 “new” listing today is worth a second look.

The Controls, One at a Time

Six controls is a lot for a fuzz. It is also, on this pedal, not remotely too many — each one does something structurally distinct, and three of them are things most fuzz pedals simply do not offer.

Relax/Push — The One That Matters

ZVEX’s own description: “This knob introduces source impedance to the signal going into the Mastotron. When fully up, the signal goes in raw… when turned down, source impedance is added as needed to ‘soften’ the input for active pickups.”

Here is what that means in plain language. Every classic fuzz circuit — Fuzz Face, Tone Bender, and their thousand descendants — presents a very low input impedance to your guitar. That low impedance is not a design flaw; it is the entire reason those pedals respond the way they do. It is why a Fuzz Face cleans up when you roll back your guitar volume, and it is why putting a buffered pedal in front of one ruins the effect. The fuzz is not just processing your pickups; it is loading them, and that loading is part of the sound.

The trouble is that this interaction is a fixed accident of whatever your guitar happens to be. A Strat with 6k single-coils loads differently from a Les Paul with hot humbuckers, which loads differently again from an EMG-equipped metal guitar, which loads not at all like a synthesiser or a DAW output. Traditionally your only options were to accept whatever you got, or to insert a buffer and lose the interaction entirely.

Relax/Push makes that interaction a knob. Turned fully clockwise (“Push”), the signal hits the circuit raw — which is what ZVEX recommends for passive pickups. Turned counter-clockwise (“Relax”), the pedal adds source impedance in front of itself, softening a signal that would otherwise be too hot and too flat. Premier Guitar’s explanation of why this matters is the clearest we have found: players with active pickups “often run into problems with over-compressed and unresponsive tones when using distortion and fuzz pedals,” because actives deliver a hotter, flatter signal that “can lead to dull, squashed sounds.”

So: actives, line level, keyboards, re-amped DAW tracks — turn Relax/Push down. Passive pickups — start with it up. But ZVEX’s own operating instructions add a wrinkle worth quoting, because it turns a fix into an instrument: “Using a guitar or bass, turn the Relax/Push knob down a bit if you need to until the fuzz sounds immediate and tight.” Even with a passive guitar, backing this off tightens the attack. It is a feel control as much as a compatibility control.

Fuzz

ZVEX calls it “this wide-range knob,” which is doing some quiet work. The range here is genuinely enormous — considerably wider than a Fuzz Face’s single gain control, and unusually usable at low settings, where most silicon fuzzes go thin and splatty. Zachary Vex’s own stated preference, in the manual: “Turn the fuzz control until you’re happy (I like it all the way up).”

PW — Pulse Width

The second genuinely unusual control. ZVEX: “Pulse Width control. You can swing this from square wave on the left to narrow pulses on the right.”

Most fuzz circuits clip your waveform symmetrically or near-symmetrically, producing something approximating a square wave. That is the classic fuzz sound: full, buzzy, harmonically dense. As you narrow a square wave into a pulse, the harmonic content shifts dramatically — fundamental drops out, upper harmonics dominate, and the sound becomes reedier, more nasal, more synthetic. Push it far enough and you land in the territory Premier Guitar described as “the soundtrack of a favorite 8-bit video game of yesteryear.”

PW is, functionally, a texture morph from Big Muff territory to chiptune territory in one sweep. If you have read our piece on the Electro-Harmonix Big Muff Pi, think of PW as the control the Muff never had.

Tone

ZVEX: “This shapes the treble without sacrificing the heavy subs.” That second clause is the important one. Most fuzz tone controls are simple post-clipping low-pass filters — turn down the treble and you lose the top, but the whole signal gets duller and the mids collapse with it. The Mastotron’s tone circuit is arranged so the low end stays put while the treble moves. Combined with the separate Subs switch, you effectively have a two-band voicing system on a pedal that only claims to have a tone knob.

Subs — The 2–1–3 Switch

A three-position toggle, and the labelling is deliberately, mischievously out of order: the positions read 2, 1, 3 rather than 1, 2, 3. ZVEX’s own explanation of what they do: “3 is huge, 2 is medium, and 1 is absolutely none left. Totally twinky.”

Premier Guitar confirmed the range is not subtle, describing it as running “the gamut from huge, window-rattling low-end to a thin, reedy chirp” and calling the difference “very dramatic.” The same switch appears on the sibling Distortron, where the reviewer noted position 3 corresponds to the Box of Rock’s maximum sub content — a useful reference point if you already own one.

Practical guidance from the manual: “use the sub switch on 3 for full heavy subs for bass or 2 if the subs are overloading your amp.” That caveat is real. Subs 3 into a small combo, or into a PA via a DI, will produce low-frequency content that some rigs simply cannot reproduce and some will actively distort trying.

Vol

Output volume, and there is more of it than you need. Note the manual’s warning attached to the strangest setting on the pedal: “For a strange effect, set the subs switch to 1 and then turn down the tone control all the way. You’ll have to turn up the volume control with this setting.” Stripping both the subs and the treble leaves very little signal, so the Volume knob exists partly to make that extreme usable.

Famous Players — Sorted by Evidence, Not by Marketing

A word about method. Brand artist pages are, as a class, the least reliable gear sources on the internet: they are marketing documents, they go stale, and they routinely list a player under a product the player has never touched. This series has caught that failure repeatedly, and we default to distrusting them.

The Mastotron is the rare case where the brand page and the independent evidence converge. ZVEX’s own artists page names precisely five acts as Mastotron users. Equipboard, working entirely from photographs, interviews and video, independently documents four of those same five plus a further list. When a manufacturer’s claim and a photograph of a working pedalboard agree, that is about as good as gear attribution gets. Here is the field, sorted by how strong the evidence actually is.

Class 1: The artist describes the pedal in their own words

St. Vincent (Annie Clark) is the strongest attribution on this pedal and one of the strongest in this entire guide, because it is confirmed from both directions. ZVEX’s artists page states plainly: “St. Vincent: Annie Clark uses a Mastotron.” And Clark herself, in an interview with The Lab magazine, gave the single best one-line description of the pedal anyone has managed: “I use – actually I think it’s a pretty cheap pedal – a Z.Vex Mastotron, and it’s like if the Fuzz Factory had girth.”

That sentence deserves unpacking, because it is a working guitarist’s summary of the design goal. The ZVEX Fuzz Factory is a legendary but famously spiky, gated, unstable device — brilliant at chaos, less good at weight. The Mastotron takes the same house sensibility and gives it a low end. “Girth” is exactly the word. If you have ever wanted the Fuzz Factory’s attitude on a part that also has to hold down a chorus, this is the pedal that solves it.

Mike Kerr (Royal Blood) is confirmed on ZVEX’s page (“Royal Blood use a Mastotron”) and, more entertainingly, semi-confirmed by Kerr himself. In a 2020 Guitar World feature, the interviewer put it to him: “Well, I know you use an Electro-Harmonix POG2 and a Z.Vex Mastotron Fuzz.” Kerr’s reply was, in full: “There you go then. So you know all you need to know.” He then refused to identify his so-called “mystery pedal,” which he has sworn never to disclose.

Royal Blood matter here more than most, because Kerr’s entire sound is one bass guitar being split and processed into what listeners hear as a full band. The Mastotron sitting alongside an Electro-Harmonix POG2 is not decoration — it is load-bearing architecture. Equipboard’s user community independently reached the same conclusion, noting that the Mastotron “excels in creating Royal Blood-like tones when paired with a Whammy or POG in -1 octave harmony mode.”

Class 2: Named by the manufacturer and corroborated by a third party

Chris Wolstenholme (Muse) appears on ZVEX’s page — “Chris Wolstenholme uses a Mastotron” — and the corroboration is unusually good: mix engineer Tommaso Colliva, discussing the recording of Drones with Sound on Sound, said “We use quite a few ZVex pedals, like the Mastotron and the Woolly Mammoth, because they have really crazy sounds, and while some of them are not controllable enough for a live scenario, they are really useful in the studio if you want very extreme sounds.”

A necessary correction while we are here. Muse’s guitar sound is Matt Bellamy‘s, and Bellamy’s ZVEX connection is the Fuzz Factory — famously built into his guitars rather than sat on the floor. The Mastotron is Wolstenholme’s, on bass. ZVEX’s own page separates the two claims in a single sentence and we should too. If you have seen the Mastotron attributed to Bellamy somewhere, that is a conflation of two different band members and two different pedals.

Matt McJunkins — bassist for Eagles of Death Metal, A Perfect Circle and Puscifer — is named on ZVEX’s artists page as a Mastotron user, complete with a supplied photograph. Third bassist on the list, which is not a coincidence.

Cage The Elephant are listed by ZVEX with the single word “Mastotron,” and Equipboard independently credits the pedal on the band’s 2013 album Melophobia. Album credits are a soft class of evidence on their own, but paired with the manufacturer listing they hold up.

Class 3: Photographic and video evidence of working boards

None of the following appear on ZVEX’s artist page, which means the evidence stands or falls on its own. It is generally good.

• Brad Paisley — the pedal is visible 4:35 into a video, catalogued by Equipboard. Of every name on this list, this is the one that will surprise people most: a country virtuoso best known for Teles and clean chicken-pickin’ running a sub-heavy silicon fuzz. It is a useful reminder that pedals do not read genre labels.
• Yvette Young (Covet) — pedalboard shown in an Instagram post. Worth noting that ZVEX later gave Young her own signature category on their site, so the relationship with the brand is documented independently even if this specific pedal is photo-sourced.
• Mark Speer (Khruangbin) — visible in a Premier Guitar Rig Rundown. We flag this one with our standard caveat: Rig Rundown pages from several eras are a headline and an embedded video, so the gear detail lives in footage we cannot transcribe. The citation is real; the confirmation is visual.
• Jimmy Smith (Foals) — Instagram photograph from the artist’s own account.
• Adam Neely (Sungazer) — walks through his pedalboard on camera between 5:00 and 5:20 of a gig vlog. Bassist. Fourth one.
• Anton Newcombe (The Brian Jonestown Massacre) — photographed in a PMT Online interview, noted for live use.

Class 4: Named in print interviews and studio gear lists

• Brad Delson (Linkin Park) — the Mastotron appears in Premier Guitar’s “In the Studio with Linkin Park” gear list. Studio lists are softer than photographs but harder than forum rumour.
• Dave Farrell (Linkin Park) — mentioned in a Bass Player interview. Bassist. Fifth.
• Brittany Howard (Alabama Shakes) — the pedal appears in her gear list from a Premier Guitar interview.

Album credits

Equipboard additionally credits Mastotron appearances on Nothing by Darkside (2025), Play by Marmozets (2017), Drones by Muse (2015) and Melophobia by Cage The Elephant (2013). Album credits are the softest class of evidence in this guide and we present them as colour, not proof — but the Drones entry is separately corroborated by the mix engineer quoted above, which is more than most album credits can say.

The pattern nobody advertises

Count the bass players. Mike Kerr, Chris Wolstenholme, Matt McJunkins, Adam Neely, Dave Farrell — five, out of a documented field of about a dozen and a half. On a pedal ZVEX sells from its guitar pedals page, with a guitar-shaped manual and a guitar-oriented product description. The most useful single fact about the Mastotron’s reputation is that its heaviest advocates are people playing four strings.

Names we did not link, and why

Tone Recipes: Nine Places to Start

All settings use clock positions. Where a setting comes from a documented source rather than from us, we say so — those are worth more than our opinions.

Where It Sits: Comparisons

Mastotron vs. ZVEX Fuzz Factory

The family argument, and Annie Clark already settled it: the Mastotron is the Fuzz Factory with girth. The Fuzz Factory is a five-knob germanium chaos engine with a Stab control that will make it oscillate, gate and self-destruct on command. It is unbeatable for sputter and squeal and genuinely difficult to keep under control. The Mastotron is silicon rather than germanium, more stable, dramatically bigger in the bottom end, and it will hold down a rhythm part. Equipboard’s user reviews put it bluntly: the Mastotron is “favored for its massive sound with octave down effects, unlike the Fuzz Factory which struggles with similar setups.” Different jobs. Many people own both.

Mastotron vs. ZVEX Box of Rock

Barely a comparison, but people ask. The Box of Rock is a JTM45-in-a-box built around clean-up from the guitar volume; it is a drive. The Mastotron is a fuzz that does not clean up much and is not trying to. Same brand, same enclosure dimensions, opposite design philosophies. If you want a Marshall, buy the Box of Rock. If you want a mastodon, you know where to look.

Mastotron vs. Big Muff Pi

The EHX Big Muff Pi is the default answer for big, sustaining, full-bodied fuzz, and it is a fine one. What it does not have is the Mastotron’s flexibility: no impedance control, no pulse width, no sub selector, and a mid-scooped tone stack that fights bass players and small amps. The Mastotron will get closer to a Muff than a Muff will ever get to a Mastotron. The Muff, on the other hand, costs a third as much and has fifty years of records behind it. See also the Green Russian for the fattest Muff variant, and the Op-Amp Big Muff for the most aggressive.

Mastotron vs. Fuzz Face-style pedals

A Dunlop JH-F1 Fuzz Face or an Analog Man Sun Face is a two-transistor circuit with two knobs, and its whole personality is the interaction between your pickups and its input. The Mastotron takes that interaction and makes it adjustable — which is either heresy or the obvious improvement, depending on your temperament. What the Mastotron will not do is the specific woody, vocal, germanium midrange of a good Fuzz Face. It is a silicon pedal and it sounds like one: harder, colder, louder, bigger.

Mastotron vs. gated and velcro fuzzes

Equipboard’s user notes credit the Mastotron with reaching “gated velcro and silicon fuzz face sounds” via the PW and Subs controls. It does get into that territory. It does not get all the way to the extremes — an EarthQuaker Devices Hoof or a Death By Audio Fuzz War will out-ugly it, and a Hizumitas does the specific Boris-adjacent doom thing better. But the Mastotron covers more ground than any of them from a single box.

Mastotron vs. modern multi-mode fuzzes

The JHS 3 Series Fuzz and Keeley Fuzz Bender both offer flexibility through switching between voiced modes — pick a flavour, then adjust. The Mastotron offers flexibility through continuous parameters that were never exposed on a pedal before. That is more powerful and considerably less friendly. If you want a fuzz you can dial in during a soundcheck, buy the JHS. If you want a fuzz you can spend a weekend learning, buy this.

Mastotron vs. the Woolly Mammoth

The comparison every bassist makes. ZVEX’s Woolly Mammoth is the company’s dedicated bass fuzz, hand-painted, considerably more expensive, and the pedal Premier Guitar explicitly invoked when recommending the Mastotron: “For players who’ve been craving Z.Vex’s Woolly Mammoth bass fuzz, the Mastotron should provide more than enough punch, power and versatility.” The Mammoth has a Pinch control where the Mastotron has PW, and the two circuits are related enough that at least one DIY kit maker builds a board that combines elements of both. Colliva’s Drones comment confirms Muse’s studio kept both on hand. The short version: the Mammoth is more specialised and more expensive; the Mastotron is more flexible and works on guitar too.

The wider ZVEX context

None of the following players are documented Mastotron users, and we are naming them purely as brand context: ZVEX’s own artist page credits Billy Gibbons with a Nano Amp and SHO, John Frusciante and Tame Impala’s Kevin Parker with Fuzz Factories, Jonny Greenwood with a Fuzz Probe, and lists Billy Corgan and Kevin Shields as owning “various ZVEX pedals.” J Mascis‘s Dinosaur Jr. are credited with a Double Rock and a Lo-Fi Loop Junky. Not one of these is a Mastotron citation. We include them because the brand’s credibility is part of why this pedal gets bought, but a Fuzz Factory endorsement is not a Mastotron endorsement and we will not pretend otherwise.

Buying Guide

Who should buy one

• Bass players who want a fuzz that does not eat the fundamental. This is the pedal’s strongest single case, and the artist list proves it. Subs 3 plus a tone control that leaves the bottom alone is a genuinely unusual combination.
• Anyone with active pickups. Relax/Push exists for you. If fuzz has always disappointed you and you play EMGs, this is the first thing to try.
• Producers and engineers who re-amp. ZVEX built the impedance control partly for exactly this. A fuzz that accepts line level without a reamp box is a studio convenience worth real money.
• Players who want one fuzz to cover a lot of ground. Square to pulse, huge to twinky, tight to woolly — the range is real.
• Anyone chasing the St. Vincent guitar sound. It is on the record from both directions. This is the pedal.

Who should skip it

• Players who want a classic, vintage-voiced fuzz. Premier Guitar’s own “skip if” was precise: skip it “if you need a more subtle, classic fuzz tone.” It is a silicon pedal with a modern personality.
• Players who hate menus. Six interacting controls with no presets is a real cognitive load on a dark stage.
• Anyone on a tight budget. $179 is not expensive by boutique standards, but a Big Muff clone at $70 will get most players 80% of the way.

What to check when buying used

Around $120 is the going used rate. Check that the LED lights and is bright — the manual uses LED dimness as its battery-change indicator, so a dim LED on a mains-powered demo is worth asking about. Confirm all six controls sweep without crackle. Note that unlike the Box of Rock, whose Drive and Boost pots crackle by design because of DC across them, the Mastotron has no documented crackle behaviour: noise on these pots is dirt, not a feature. Check the four base screws are present and the battery clip is intact. And confirm the DC jack is solid, because it is side-mounted and takes a lot of abuse.

Living With It

Power and board layout

At roughly 1 mA, the Mastotron is effectively free on any power supply. The side-mounted jacks are the real board-planning constraint: this is a 4.70″ × 2.38″ enclosure with connections coming out of the sides rather than the top, so it wants a little more horizontal room than its footprint suggests.

Battery life and the unplugging rule

The manual ends with an instruction in bold that people ignore: “Remember to unplug your Mastotron’s input jack when not in use to save battery life!” Like most battery-capable pedals, the input jack is the switch — leaving a cable in the input drains the battery even when the pedal is bypassed. At 1 mA the battery will still last an unusually long time, but the rule still applies.

Placement in the chain

ZVEX is unusually direct about this: “I recommend that you try the Mastotron first in your pedal chain, just after the guitar.” That is standard fuzz advice and there is a technical reason for it here — the whole point of Relax/Push is to interact with your instrument’s source impedance, and a buffer in front of the pedal removes the variable it was built to control. Put it first.

The manual then immediately contradicts its own advice in the most ZVEX way possible: “Try putting weird effects into the Mastotron and adjust the Relax/Push knob for best interfacing.” Which is to say — the impedance control is precisely what lets you break the rule, because you can re-tune the input for whatever is now feeding it. Both statements are true.

The amp setting matters

“Set the amp for a warm clean tone on bypass,” says the manual, and Premier Guitar’s testing bore this out — the pedal was run into channel 2 of an Egnater Tourmaster with a 4×12. A Mastotron into an already-distorting amp is a legitimate texture, but it is not the reference sound. Get it working over clean first.

Subs and your rig’s limits

Worth repeating because it causes more complaints than anything else: Subs position 3 produces low-frequency content that many amps physically cannot reproduce. If the pedal sounds flabby, farty or oddly quiet, the amp is likely being asked to do something it cannot. Drop to position 2 before concluding the pedal is broken.

Frequently Asked Questions

The Verdict from the Archives

Premier Guitar gave the Mastotron 4.5 out of 5 in June 2009 and summarised it this way: buy if “an inexpensive, tight fuzz with signature tone and lots of control is the name of the game,” and skip if “you need a more subtle, classic fuzz tone.” Seventeen years and one continuous production run later, that verdict has held up better than most.

What the review could not have known in 2009 is which players would eventually pick it up, or that the pedal’s strangest feature would turn out to be its most durable one. Every fuzz on the market gives you a gain knob. The Mastotron is one of the very few that gives you a knob for the thing happening before the gain knob — the invisible handshake between your pickups and the first transistor, which every other fuzz on your board leaves entirely to chance.

Annie Clark called it a cheap pedal with girth. She was being modest about the pedal and generous about her own gear budget, and she was also, as usual, exactly right.