The ThorpyFX Heavy Water is a dual boost pedal from UK maker ThorpyFX, designed by Adrian Thorpe and first announced in August 2019123. It puts two boosts in one compact enclosure: a dirtier germanium-diode boost on the left side and the high-headroom clean boost from ThorpyFX's The Dane overdrive and boost pedal on the right4. Each side can be used independently or combined, so a player gets a clean boost, a gritty boost, or both stacked, all from one box on the pedalboard5.
ThorpyFX describes the current MKII as "two boosts in one, the perfect solo pedal for your gig board"6. In a technical piece for Guitar.com, Thorpe himself explained the concept: the full-range booster "makes your guitar signal louder overall, but gives you scope to control the low frequencies"7.
Two boosts in one enclosure
The left side of the Heavy Water provides more volume but uses germanium clipping diodes for a grittier, dirtier character, what Guitar Pedal X later described as a boost that "has a little more bite"43. The right side carries the high-headroom clean boost taken from the Dane, a circuit that leaves the core tone largely intact4.
Guitar World's review found that, set at minimum, the clean boost "brings in a small but definite boost that enhances the sound, immediately making our amp" work harder without undue alteration of tonal character1. Guitar Pedal X's Stefan Karlsson reported using the left, germanium side as almost always on, with the right-side Smooth Dane boost brought in only about 5 percent of the time, with both sets of Boost and Lows controls set between 8 and 9 o'clock8.
Because the two channels can be stacked, the pedal offers what Guitar Pedal X calls "3-way action": germanium alone, Dane alone, or both together, with a second footswitch for mixing things up on the fly73.
The controls: Boost and Lows on each side
The pedal carries four knobs in all: two boost-level knobs and two Lows knobs, one pair per side9. Each side also has its own engage footswitch7.
| Control | Side | What it does |
|---|---|---|
| Boost | Harmonic Germanium (left) | Sets the amount of the grittier germanium boost17 |
| Lows | Harmonic Germanium (left) | Thickens the boost effect97 |
| Boost | Smooth Dane (right) | Sets the amount of the clean Dane boost5 |
| Lows | Smooth Dane (right) | Thickens the boost effect9 |
| Engage footswitch | Each side | Switches that side on and off independently5 |
The Lows controls are the tone-shaping half of the pedal: as Guitar.com's news piece put it, they "can be used to thicken the boost effect," letting a player add low-end weight to whichever boost is engaged rather than simply making everything louder9.
Power, bypass and connections
The Heavy Water runs on an external 9V DC power supply, which is not supplied, and there is no battery compartment13. Adrian Thorpe explained the company's reasoning in a Stompbox Book interview: "We used to. We don't any more. It's a waste."10 The pedal uses buffered bypass rather than true bypass1, and the MKII draws 24mA6. Connections are a standard input and standard output on the reviewed version1, and ThorpyFX pedals use top-mounted jacks to save pedalboard space10.
No battery option means the Heavy Water needs a spot on a power supply from day one. At 24mA it is light on current, so it fits easily on most isolated supplies6.
History and versions: from The Dane to the MKII Artwork Edition
The Heavy Water's circuit has a documented lineage. Guitar Pedal X's origin story traces it to ThorpyFX's Chain Home Tremolo, whose volume drop prompted a High Headroom Dane Smooth Boost used to compensate, a circuit that then grew into its own pedal11. Daniel Steinhardt of That Pedal Show, naming the Heavy Water among his top five stompboxes, put it more simply: "I think this started life as the boost side of the ThorpyFX Dane [overdrive and boost] and then they added another boost"12. ThorpyFX itself says the pedal was "designed to meet the requests we were receiving to release the Boost side of the DANE as a standalone pedal"6.
The timeline of the pedal's versions:
- 2019: Heavy Water Dual High Headroom debuts, combining the Dane's clean boost with a germanium-diode boost in a smaller enclosure than the wider Dane49.
- 2022: ThorpyFX adds a Custom Shop version with TRS inputs and outputs for players using loopers6.
- 2025: MKII Artwork Edition arrives with new main artwork, water droplets on the top, and decorated side panels; the circuits are unchanged137.
Guitar Pedal X was explicit that the MKII refresh is cosmetic only: "these are the exact same circuits - where simply their outward appearance has been changed"13.
The TRS Custom Shop version
For players with switching systems, the 2022 Custom Shop version offers TRS inputs and outputs that let a looper activate the two sides independently6. ThorpyFX's guidance is straightforward: "For those that use the pedal normally on a traditional pedalboard, choose NORMAL IO. In this case choose TRS In/OUTS" for looper users6.
What reviewers said
Guitar World's review called it "one of the most versatile boost pedals we've seen, capable of everything from always-on tone enhancement to kicking in a full-on screamfest"1. Premier Guitar's reviewer praised the build, citing "the clever and seemingly bulletproof custom enclosure to the top-quality materials and pristine circuit execution," and noting that "what sets Heavy Water apart is designer/builder Adrian Thorpe's uncompromising approach"2. Guitar Pedal X found it "serves beautifully as a superb always-on tone enhancer" delivering added harmonics and texture8.
For more on the category, see boost pedals; the Dane circuit the right side comes from is covered on the ThorpyFX The Dane page.
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Questions
Does the ThorpyFX Heavy Water take a battery?
No. The Heavy Water requires an external 9V DC power supply and has no battery compartment. Adrian Thorpe has said the company dropped battery compartments because they are a waste, so all current ThorpyFX pedals run on external power only.
Is the Heavy Water true bypass or buffered?
The Heavy Water uses buffered bypass rather than true bypass. A buffer keeps the signal strong through long cable runs and pedal chains, though players who prefer a fully passive signal path when the pedal is off may prefer true bypass designs.
How much current does the Heavy Water draw?
The current Heavy Water MKII draws 24mA, according to ThorpyFX's product page. That is modest by modern pedal standards, so it places little demand on a typical isolated power supply feeding a pedalboard.
What is the difference between the Heavy Water and The Dane?
The Dane is an overdrive and boost pedal; the Heavy Water takes the Dane's high-headroom clean boost circuit and puts it in a standalone pedal, then adds a second, grittier germanium-diode boost on the other side. The Heavy Water is also smaller than the wider Dane enclosure.
Can both sides of the Heavy Water be stacked?
Yes. Each side can be used independently or combined, giving three usable states: germanium boost alone, clean Dane boost alone, or both stacked together. Each side has its own engage footswitch, so you can mix things up on the fly.
What does the TRS version of the Heavy Water do?
For 2022 ThorpyFX added a Custom Shop version with TRS inputs and outputs, aimed at players using loopers. The TRS connections let a switching or looping system activate the two boost sides independently by remote control rather than only via the footswitches.
Sources (13)
- ThorpyFx Heavy Water review, Guitar World, 2020-05-07
- One Boost Pedal to Rule Them All?, Premier Guitar, 2020-04-01
- Guitar Pedal X, Guitar Pedal X, 2026-09-23
- Thorpy FX launches the Heavy Water Dual High Headroom Boost pedal, gearnews.com, 2019-08-05
- ThorpyFX Introduces the Heavy Water Dual High Headroom Boost, Guitar World, 2019-08-06
- HEAVY WATER, ThorpyFX, 2022
- What does a guitar boost pedal actually do?, Guitar.com, 2024-04-03
- Guitar Pedal X, Guitar Pedal X, 2024-04-22
- ThorpyFX takes the plunge with Heavy Water Dual High Headroom booster, Guitar.com, 2019-08-06
- Thorpy FX, Stompbox Book (stompboxbook.com), 2020-04-12
- Guitar Pedal X, Guitar Pedal X, 2024-04-08
- Daniel Steinhardt reveals his top 5 pedals (from the past 5 years), Guitar World, 2025-05-29
- Guitar Pedal X, Guitar Pedal X, 2025-05-08
