REVIEW: ZVEX Effects Mastotron Pedal

The fuzz coming out of this pedal is itchy, like wearing a heavy wool sweater directly against your skin. Aside from scratching myself, playing through a torn speaker was the first thing I thought about when engaging the Mastotron. As a frame of reference, all dials were set halfway with the subs toggle on 1. The first part of this example is clean for reference followed by the fuzz.


One thing that impressed me that you don’t get playing through a torn speaker is surprisingly long sustain. Cranking the volume to max boosted the level as one would imagine, but not as much as I expected. Rather it was like opening the throttle, in that the tone became more aggressive.

Dialing tone down reduced upper frequencies resulting in a muffled sound that still maintained clarity despite its limited range. Cranking the tone gave energy to the upper frequencies but kept them in check so as not to break into harsh and piercing highs which lesser pedals can have problems handling well.


The pulse width dial offers wide square waves at one end of the spectrum to narrow waves at the other. Audibly this can be compared to degrees of speaker deterioration which affects the clean/dirty ratio and sustain. At its widest setting the signal was relatively clean and chimey and Johnny was able to get more nuanced playing to come through. An initial degree of fuzz was present which can be controlled through dynamics. Playing softer keeps the fuzz in check while pounding the strings brings out more grit. At the narrow wave setting it’s pure fuzz. Great sustain was held to a point at which a gate-type effect cut off the sound completely. Light nuances possible in the wide setting barely came through as drops of static and muting notes and chords put an immediate end to all sound – no ringing out whatsoever.


The fuzz dial affects the sonic quality of the dirt. At its lowest setting the sound was somewhat muffled as if the amp was turned away from us. At the highest setting it was full on in-your-face dirt: brighter and richer, but trashier as well.


The Relax/Push control affects source impedance or how the signal is allowed to flow into the fuzz monster’s den of sin. In full “Relax” mode, impedance was introduced to the signal resulting in what sounded like a 50/50 balance between guitar and fuzz. “Push”ed to max, the signal was mostly raw and sounded more like a 10/90 split.


Finally, the subs toggle affects the amount of bass oomph! Setting 1 was neutral. 2 gave a big boost to the bottom end and 3 promoted a massive boom down low. Listening to the audio sample on computer speakers does not do the audio justice – this control makes significant differences to the tone.



Pulling apart velcro… running hemp twine between your fingers…tuning the radio between stations… These scenarios illustrate the audible character of the Mastotron. The fuzz is unique making it more of a specialty pedal, but numerous controls that work interactively help you dial in your trash to taste, from harmonically rich grunge to off-the-wall nearly synth-sounding static. Visually, I can imagine some really trippy fuzz art and would expect as much from ZVEX, a leader in hand painting pedals, but sadly the rather straightforward print job does little to support this reputation. The wide format is great for placement of the controls and totally fine for using on the floor but is less than ideal for pedalboards which favor a vertical design. Ultimately it’s about the quality of tone and construction and ZVEX scores for what counts.

PROS: Solid build. Wide range of tonal possibilities. Maintains harmonic integrity despite heavy fuzz.

CONS: Disappointing graphics (considering ZVEX’s history for some of the coolest looking pedals around). Wide form factor less attractive for pedalboard use. Requires a screwdriver to get at the battery. Small SUBS switch buried between dials is hard to access.

MSRP – $149

Dan Coplan is senior staff writer at SMG. Dan is a Los Angeles based cinematographer and self-admitting guitar junkie. Email:

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