Thorpy FX Heavy Water Dual High Headroom Boost

The Thorpy FX Heavy Water Dual High Headroom Boost is a boost pedal that packs two separate boost circuits into one compact enclosure: a clean, high-headroom boost and a dirtier boost that uses germanium diodes for a grittier character¹. Each side has its own footswitch, so you can use them one at a time or stack both for a large amount of gain into the front end of your amp¹².

UK pedal maker Adrian Thorpe, known as Thorpy FX, created the Heavy Water¹. It is a small-format pedal that packs two boosts into one enclosure: a clean boost and a dirty boost, with the dirtier, germanium diode-enhanced boost on the left side of the enclosure³¹.

Two boosts in one enclosure: one clean, one dirty

The Heavy Water combines two boosts in one compact enclosure: a clean boost, and a second boost with some extra grit for situations where you need added grit along with the level push¹³. The left side of the pedal is the dirtier germanium diode-enhanced boost, giving it a grittier, dirtier character, while the right side is the clean boost¹³. Guitar World describes the pairing as a clean boost with a second boost that features germanium diodes in its circuitry for a different character².

Each side carries its own controls:

The two circuits are independently footswitchable, so the pedal works as three boosts in one: Smooth Boost, Harmonic Boost, or both together⁵⁶. Gearnews notes one use is simply giving your amp a much needed kick, with the choice of two voices¹. With both boosts engaged, Guitar World's reviewer found it "capable of delivering a ridiculous amount of gain that will truly pummel your amp"².

In a Guitar World interview, Daniel Steinhardt of That Pedal Show described how the pedal responds to playing dynamics: "the richness of the boost just has a clarity to it that is completely dynamic off the volume control"⁷. Guitar Pedal X has also written of the Heavy Water working as an always-on tone enhancer delivering added harmonics and texture⁸.

Power: external 9V, no battery

The Heavy Water requires an external 9V DC power supply, and the adaptor is not supplied with the pedal¹². There is no battery option, so plan for a free 9V output on your pedalboard supply¹.

Where the circuit comes from, and the MKII

The Heavy Water's family tree runs through several earlier ThorpyFX pedals. Guitar Pedal X's origin story traces it back to the Chain Home Tremolo, whose volume drop prompted a High Headroom Dane Smooth Boost used to compensate; requests for a standalone Dane boost then became the Heavy Water, with its Smooth Boost, Harmonic Boost and both-together modes⁵. The Dane circuit itself drew on the Peacekeeper and Gunshot circuits as early source inspirations⁵. Guitar.com's reviewer likewise notes the pedal was built after players asked for the Dane's high-headroom boost circuit in its own box, with germanium diodes added for a grittier boost⁶.

In May 2025 ThorpyFX released the Heavy Water MKII Dual High Headroom Boost as part of its MKII Artwork Edition series⁴. The MKII is a cosmetic refresh, not a circuit change:

• New main artwork featuring water droplets, plus decorated side panels⁴
• The exact same circuits as the original, with only the outward appearance changed⁴
• Sound, feel and function identical to the predecessor⁴
• Priced at £219.99 at launch⁴

Guitar Pedal X's Stefan Karlsson called it his favorite Heavy Water Dual Boost, "further beautified" by the MKII artwork⁴. ThorpyFX's own product page describes the current Heavy Water Dual Boost as "two boosts in one, the perfect solo pedal for your gig board"⁹. The original launch price was listed at an RRP of 189.99, with the currency not stated¹.

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