ZVEX Distortron

The ZVEX Distortron is a compact distortion pedal from ZVEX, built as a modified version of the distortion engine in the ZVEX Box of Rock. It arrived in 2009 as part of ZVEX's lower-cost Vextron series¹, and it keeps the Box of Rock's core dirt circuit while adding two switches: a gain boost and a three-level Subs control for the low end².

ZVEX founder Zachary Vex describes the pedal as "highly specialized to simulate the everything-on-ten sound of a classic Marshall JTM45 amplifier"³. The maker also suggests where to put it on a board: "Try it last in your chain, and beat it up with your other effects... it stacks like a dream."²

The controls: gain, gain boost and Subs switches

The pedal keeps the control set simple: three knobs, Volume, Tone and Drive³. The two switches are where it differs from the Box of Rock.

ZVEX describes the improvements over the Box of Rock engine as "a gain boost switch for added sizzle and a sub control switch with 3 levels," with the Subs switch there to reduce the "flubbiness" that occurs when using amps with heavy low-end response².

For players comparing it directly with the Box of Rock, DIY builders who traced the circuit found that with the gain switch off and the Subs switch at 3, the pedal is exactly the dirt side of the Box of Rock⁴. The Subs positions below 3 simply thin the low end, which is useful with amps that already push a lot of bass.

What the circuit is

The Distortron is built from cascaded Super Hard-On boost stages, the same topology as the Box of Rock¹. DIY tracing of the vero layout found that Q1 is "basically a slightly modified Super Hard On," and that a 470k resistor and 470pF capacitor in the middle of the board couple the first and second gain stages⁴.

There is no official schematic. The DIY community's position on it is blunt⁴:

Guitar FX Layouts, on the vero layout published in October 2013⁴

That layout was published with corrected capacitor values after earlier published values were questioned, and it describes the circuit as "1:1 with added switches for more gain and thinner low frequencies" against the Box of Rock dirt side⁴.

What reviewers said

Premier Guitar reviewed the Distortron alongside the ZVEX Mastotron silicon fuzz in September 2026, and the review's overall picture was of a classic rock pedal in a small box: "the Distortron is a classic rock powerhouse in a compact pedal form"³.

The reviewer's findings on how it responds:

• It "clearly shines with lower output pickups," with pick attack much more evident, sustain and decay considerably more natural and smooth, and great punch in the mids³.
• It "sounds fantastic in low- to mid-gain applications," and "really, really good" in high-gain situations³.
• Even at higher drive settings with hot pickups, "the tone never muddied up and lost its articulate nature"³.

The review's verdict came down to what kind of distortion a player wants: buy it if "you want classic rock tones in a touch-sensitive, articulate drive," and skip it if you need a more modern distortion sound³.

DIY builders who built the circuit from the vero layout reported similar things, in their own words. One described it as "a 'cleaner' distortion compared to something like a Rat. Very crisp and bright," with "tonnes of low end, even on the lowest sub switch setting"⁴. Another found "a huge range of sounds from it, from subtle warming/thickening, through to overdrive, bluesy crunch, modern rock and dirty grungy sounds"⁴. A later builder reported that "this thing sounds amazing... and it's LOUD. I need to keep the level at about 9:00. It's got a really satisfying feel" and that it cleans up great⁴.

Building and modding one

The Distortron has a following in the DIY community. PedalPCB sells a PCB for a distortion pedal it lists as a comparison to the ZVEX Distortron, with a Gain toggle that switches between high and low gain⁵. The Guitar FX Layouts vero layout is the other common starting point⁴.

Builders have also documented mods and quirks:

• The gain pot is a C5K anti-log taper, which some builders have struggled to source; one substituted a 10K reverse-log pot and reported "nice crunch" at the bottom and "super thick fuzz-like" response at the top⁴.
• The gain switch is wired SPDT on-on, with Hi/Lo2 to the center lug⁴.
• The 470k tone stack resistor is a popular mod point. Builders report 200k "sounds like a Marshall with its output stage distorting," 750k sounds tight and starts sounding pretty modern with the 470pF cap changed to 1n, and 1M gives less "meaty/oomph" at low gain but stays clear even with the hi-gain switch engaged⁴. At 0k the circuit "comes closer to a fuzz" and one builder said it sounds a lot like Queens of the Stone Age⁴.
• Not every build goes smoothly: some builders report high squealing, and one reported a build producing only a low noise signal⁴.

Related ZVEX pedals

The Distortron sits inside a small family of ZVEX circuits. The ZVEX Box of Rock is the parent pedal, a distortion plus boost whose dirt engine the Distortron borrows². The ZVEX Double Rock Vexter is a two-in-one pedal with configurable Distortron and Super Hard-On channel options, originally made for J Mascis⁶. The ZVEX Vextron Distortron page covers the Vextron series version of this circuit.

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