KMA Machines Wurm

The KMA Machines Wurm is a high-gain distortion pedal built as a modern take on the Boss HM-2 Heavy Metal, the pedal behind the Swedish death metal "buzzsaw" guitar sound. KMA, a Berlin-based company, released the Wurm in 2018 and kept the HM-2's active dual-band EQ section while adding two more bands, giving four EQ controls where the Boss original had two¹². The original Wurm is now discontinued, but its circuit lived on through the WURHM limited edition, the Guardian of the Wurm and the Wurm 2³⁴.

KMA described the pedal in its own words when the Wurhm launched:

A Boss HM-2 with a four-band active EQ

The Boss HM-2, released in 1988, is the cornerstone of the Swedish death metal buzzsaw sound, with tons of gain and the ability to boost or cut mids using its H (high) Color Mix control¹⁰¹¹. Its chainsaw sound comes from the resonant peaks of its active EQ stage, and treble must be maxed to achieve the signature sound¹². The HM-2's EQ is a two-band affair, and that limitation is what the Wurm set out to fix: KMA integrated the original's active EQ with two more bands for a total of four EQ controls, Lows, High Mids, Low Mids and Highs².

Each band covers a set frequency range, which is what makes the Wurm more flexible than the pedal it honors¹³¹⁵:

Pedal of the Day's reviewer called the EQ section "the real beauty here," noting the four fully customizable sliders and the internal dip switches that let you activate or deactivate the classic HM-2 EQ⁴². Beyond the chainsaw setting, the Wurm's thick walls of gain and sustain suit styles well outside death metal, from shoegaze to prog rock¹⁴.

The controls and dip switches

The front panel keeps the HM-2 spirit but renames the gain control: TERROR dials in the malice and the evil distortion sound⁸¹. Cranking it up produces extreme gain⁸. The LOWS and HIGH MIDS controls are the ones that matter most for the classic character; KMA's own guidance is to crank the LOWS and the HIGH MIDS for the chainsaw sound³.

The internal DIP switches are the Wurm's main configurability feature, and they decide how the High Mids band behaves³⁵:

• Switch 1 on, Switch 2 off: selects the WURHM high-mids mode, KMA's own designed mid-band¹
• Switch 1 off, Switch 2 on: gives the classic HM-2 chainsaw high-mids character¹
• Both switches on: gives three bands controllable via the HIGH MIDS control³

MusicRadar noted at the Wurhm launch that the WURM was already known for its configurability, and the dip switches are where that lives: they switch between the original HM-2 high control and the WURM mid-band¹⁵³.

Versions: Wurm, Wurm 2 and Guardian of the Wurm

The Wurm line went through several stages after the original 2018 pedal:

The WURHM, launched in November 2020, took the HM-2's hallmarks into what MusicRadar called "new realms of versatility and sonic brutality," with two more EQ bands than the Boss original and internal DIP switches for more tone control¹⁶. It marked the milestone of 1000 Wurm units made⁵.

The Guardian of the Wurm is a souped-up version of the KMA Machines Wurhm²⁰. It carries over the Wurm's four-band active EQ and adds a 3-way clipping toggle offering Silicon, Asymmetric and OFF modes²¹¹⁷⁹. An EQ Style control selects between HMII, Both and KMA voicings¹³, and its two onboard effects can be run independently or in "Synched Mode", where both turn on whenever the pedal is engaged¹⁷. Like the Wurm, it is built around the Boss HM-2 "chainsaw" circuit¹⁶⁵.

The Wurm 2, released in March 2022, moved the voice switching from the inside to the outside: an external three-way switch flicks between chewier (HM-II) and slightly more balanced (KMA) distortions, with a Both setting that fattens the distortion with both voices¹⁹. MusicRadar described it as "the Wurm returns in a smaller enclosure with a heap of features for high-gain, extreme metal misadventures"¹⁸. It also carries an internal dip switch that activates an input filter to tame high frequencies at extreme settings².

What reviewers said

Published reviewers were consistently positive across the line:

• Pedal of the Day on the original Wurm (February 2020): "Hats off once more to the fine folks at KMA Machines, this thing really rips"⁴
• Pedal of the Day on the Guardian of the Wurm (September 2021): "the Guardian of the Wurm takes high gain into the stratosphere and beyond," and called it "a spectacular piece of gear"¹³
• Guitar Pedal X on the Wurm MK2 (2024 and 2025 roundups): "really expansive" and "Just hugely potent!" with "resulting tones really top-tier overall"²²²³

RockBoard's PedalPedia entry for the Wurm 2 says that when it comes to the Boss HM-2 MIJ sound it is "absolutely on the money," and lists a demo by Rabea Massaad alongside a German-language review by bonedo¹⁴.

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