Boss HM-2 Heavy Metal

The Boss HM-2 Heavy Metal is a distortion pedal introduced by Boss in 1983, delivering what the maker describes as raw, aggressive distortion with a uniquely voiced midrange and a powerful low end¹. Its reputation rests on one sound above all: with all knobs maxed, Boss says it pummels an amplifier's input to produce the signature "chainsaw" tone that defines the Swedish death metal guitar sound¹. Guitar.com notes the original is endearingly referred to as the "Swedish Chainsaw" and is most associated with Swedish death metal².

The pedal's standing in metal history is not just fan lore. MusicRadar calls it one of the most important pedals in the history of metal guitar, foundational to death metal, and famously used on Entombed's 1990 debut album Left Hand Path³. MusicRadar also reports that the HM-2's tone spawned the Swedish death metal sound's chainsaw wall of distortion, pioneered by bands like Dismember and Entombed⁴. Premier Guitar's reviewer adds that the original was among the first pedals to wear the amp-in-a-box mantle⁵.

The chainsaw distortion behind Swedish death metal

The HM-2's place in metal was earned in Sweden in the late '80s and early '90s. Mattias Johansson, speaking to Boss's own articles site about growing up in Sweden, said the pedal was monumental to him and his friends, and recalled the recipe plainly⁴²¹²:

Mattias Johansson, in a Boss interview¹²

He described running the pedal with the controls set to maximum, or "dimed," into a Peavey Bandit to sound like Entombed¹². RockBoard's PedalPedia makes the same connection from the other side, noting that from its brutal, grinding distortion tones, bands like Dismember and Entombed birthed Swedish chainsaw metal¹³.

The pedal's reach went well beyond death metal. Producer Tom Dalgety told Boss he used the HM-2 on bass for the Pixies' album Head Carrier, easily heard on the track "Baal's Back"¹⁴. He also liked using it as a Rangemaster-style treble booster by turning the high frequencies up with the H Color Mix knob and the distortion down to about ten o'clock¹⁴. MusicRadar reports the same pedal that produced such brutal tones was also in David Gilmour's touring rig at one point¹⁵, and Guitar World notes he used it on the '80s albums About Face and A Momentary Lapse of Reason¹⁶.

On the used market, MusicRadar listed original HM-2s at £150 to £250 (used) in a 2018 history article¹⁷.

The controls: two Color Mix EQ knobs

The original pedal has four knobs: Level, Lows, Highs and Distortion¹⁸. What sets it apart from most distortion pedals is the pair of EQ controls Boss called "Color Mix." Catalinbread, whose Carbide pedal is built around the HM-2 circuit, explains the layout:

The Color Mix controls are unusually powerful. Guitar World reports they offer plus or minus 20dB of boost or cut to the distortion circuit¹⁶, and Gearnews describes the same dual control with the same range on the original version¹⁹. The H knob is also doing more than its label suggests: Catalinbread notes it actually controls two different bands simultaneously, at 958Hz and 1279Hz²⁰. TONEHOME highlights the ability to boost or cut mids using the H (high) Color Mix knob⁷.

Under the hood, Guitar Pedal X describes the Low and High EQ knobs as studio console style gyrator controls²¹. That gyrator tone stack is a distinctive part of the circuit: a DIY analysis on the Tagboard Effects blog, building a simplified "HM-2 Lite," noted how much smaller the circuit would be without the gyrator tone stack the original uses²².

How the circuit clips

The HM-2 is a development of the core idea behind the Boss DS-1, but MusicRadar's history of the circuit says it goes overboard, with soft clipping diodes, hard clipping and crossover distortion combining to make the chainsaw sound¹⁷. Guitar Pedal X likewise calls it quite a hard-clipping device, producing what it describes as a distinctive Twin-Peaks Frequency Output Shape²³.

That combination of clipping types into a hard-edided, mid-heavy output is what players hear as the chainsaw character. The DIY community has kept the circuit alive in other forms: the Tagboard Effects HM-2 Lite was judged by mirosol to have output level and gain sufficiently close to the original, though the original's Color Mix L/H controls boost the Qs of their frequencies a lot more²². Several makers have built expanded HM-2 circuits, including Catalinbread's Carbide, offered as chainsaw distortion tones²⁴, and KMA Audio Machines' Wurhm, an HM-2 tribute whose original circuit KMA describes as a key element of the Swedish chainsaw metal sound²⁴.

The HM-2W reissue and what replaced the original

Boss discontinued the original HM-2 after a production run dated differently by different accounts: Boss itself says 1983 to 1991⁸²⁵⁷, Wren and Cuff says the last units rolled off the line in 1991⁸²⁵⁷, while TONEHOME lists production ending in 1993, with Taiwan-made units built from 1988 to 1993 and Japan-made units from 1981 to 1987⁷. TONEHOME also reports the Boss MT-2 Metal Zone replaced it, offering a similar midrange control⁷.

The story did not end there. In November 2020, Guitar World reported that Boss president Yoshi Ikegami had confirmed a Waza Craft version of the HM-2 was in the works, to be launched the following year, and that for the first time the company would seek input from fans of the pedal¹⁶. The resulting HM-2W reissue carries the same chainsaw lineage: Gearnews describes its aggressive, so-called chainsaw sound as characteristic of Swedish death metal²⁶. Guitar World's review lists the HM-2W at $179, with input, output and power sockets¹⁰. Boss has also brought the HM-2 into its PX-1 Plugout FX system as a Model Pass effect²⁷.

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