The MXR Brown Acid Fuzz is a limited-edition fuzz pedal from MXR, released through the company's Custom Shop line in October 2019. It is a silicon fuzz circuit built to recall the fully saturated fuzz tones favored by 1970s UK rock bands, in the vein of Black Sabbath, and it shipped in a brown regular-sized MXR metal enclosure with psychedelic artwork by Bay Area artist Alan Forbes12.
Only 500 units were made, and it was sold for a limited time only through select dealers23. It is a discontinued, collectible pedal rather than a current catalog item, so it now turns up on the secondhand market.
A 70s-style silicon fuzz
The circuit is silicon-based, built on what Guitar World reported as "a classic 1970s UK fuzz circuit"3. gearnews described it as "a silicon fuzz circuit in the vein of UK rock bands from the 1970s," designed to recall the fully saturated fuzz tones of that decade, à la Black Sabbath1.
MusicRadar traced the lineage further: the pedal riffs on old-school British fuzz tones in the fashion of the Colorsound Supa Tonebender Fuzz, which itself riffed on early '70s EHX "Ram's Head" Big Muff tones2. Guitar World's writer made a similar guess, betting the circuit is based on Colorsound's mid-'70s Supa Tonebender, which delivered Muff-like fuzz with additional low end, and calling it a good choice for doom, stoner and classic metal players on both guitar and bass3.
Jim Dunlop's own marketing copy leaned into the theme:
"Whether you want to ride droning power chord currents across the universe or summon burly grooves at an ancient altar, this pedal has all you need for your musical invocations."3
The controls: Output, Fuzz and Tone
The Brown Acid Fuzz keeps things simple with a three-control layout: knobs for Output, Fuzz and Tone143. Guitar World called it "a no-nonsense control array of output, tone and fuzz," and guitar.com summed up that the three knobs let you shape the sound to your liking34.
| Control | What it does |
|---|---|
| Output | Sets the overall level51 |
| Fuzz | Sets the amount of fuzz51 |
| Tone | Shapes the frequency balance1 |
That three-knob arrangement is a common one in MXR's fuzz range. The Custom Shop Sub Machine, for example, carries Volume, Tone and Fuzz controls, with its Tone control carried over from the La Machine Fuzz Tone6. The later Custom Shop Hybrid Fuzz goes even simpler, with just Output and Fuzz controls5.
A limited run with Alan Forbes artwork
The pedal's look is as much a part of its identity as its circuit. It arrives in a brown regular-sized MXR metal enclosure adorned with a trippy design from San Francisco artist Alan Forbes, known for his psychedelic poster art24. gearnews called the graphics "retro," crediting Forbes as a legendary Bay Area artist1.
The run itself was tightly limited:
- Only 500 units made2
- Available for a limited time only3
- Sold only through select dealers2
- Priced at $149 street in the US, £149 street in the UK, at launch (October 2019); guitar.com gave the list price as $149.9914
How it compares in the MXR fuzz range
The Brown Acid Fuzz sits in a crowded MXR fuzz lineup. Where it is a silicon circuit aimed at 1970s UK saturation, the MXR Custom Shop Hybrid Fuzz that followed in 2023 combines one germanium transistor and one silicon transistor in a Fuzz Face based circuit, with only Output and Fuzz controls51. Other Custom Shop entries like the Sub Machine and La Machine are octave fuzzes, adding an octave-up mode on top of the fuzz voice67.
What reviewers said
Published coverage of the Brown Acid Fuzz was largely news reporting rather than full reviews, and the writers were candid about that. gearnews' writer liked the look but said he would have to play through one to judge how it feels and reacts to his guitar1. Guitar World's speculation about the Supa Tonebender lineage was likewise flagged by the writer as an educated guess rather than a confirmed finding3.
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Questions
How many MXR Brown Acid Fuzz pedals were made?
It was a limited edition of 500 units. MXR announced it through the Custom Shop line in October 2019, and once those 500 pedals sold through, the run was finished. It was also sold only through select dealers rather than every MXR retailer.
Is the MXR Brown Acid Fuzz silicon or germanium?
It is a silicon-based fuzz. Guitar World described it as a silicon fuzz pedal based on a classic 1970s UK fuzz circuit, and gearnews called it a silicon fuzz circuit in the vein of UK rock bands from the 1970s. MXR's later Custom Shop Hybrid Fuzz is the one that mixes germanium and silicon transistors.
Does the MXR Brown Acid Fuzz work with bass?
Yes. MusicRadar reported that the pedal is voiced for bass and guitar, and gearnews noted you should be able to use it on both instruments. Guitar World's writer guessed the circuit's Supa Tonebender lineage would suit doom, stoner and classic metal players on guitar and bass alike.
What power does the MXR Brown Acid Fuzz use?
It takes nine-volt power, as reported by guitar.com when the pedal went on sale. No current draw, polarity or battery details were published alongside it, so the nine-volt requirement is the only confirmed power fact.
Who did the artwork on the MXR Brown Acid Fuzz?
Alan Forbes, a Bay Area artist known for his psychedelic poster art. The pedal comes in a brown regular-sized MXR metal enclosure adorned with his trippy design, which is part of what made the limited run distinctive alongside its 1970s fuzz circuit.
What is the MXR Custom Shop Brown Acid Fuzz?
It is the same pedal. The Brown Acid Fuzz was released through MXR's Custom Shop line, so press coverage names it both as the MXR Brown Acid Fuzz and the MXR Custom Shop Brown Acid Fuzz. It is a silicon fuzz with Output, Fuzz and Tone controls, limited to 500 units.
Sources (7)
- MXR limited edition Brown Acid Fuzz: Seventies Sabbath tones!, gearnews.com, 2019-10-02
- Bust down the doors of perception with MXR's Brown Acid Fuzz pedal, MusicRadar, 2019-10-02
- MXR drops psychedelic Brown Acid Fuzz, Guitar World, 2019-10-02
- MXR’s Brown Acid Fuzz is now available, guitar.com, 2019-10-01
- MXR’s new Hybrid Fuzz pedal comes with just one fuzz control, Guitar.com, 2023-06-06
- Dunlop Releases the Sub Machine Fuzz, Premier Guitar, 2015-02-13
- MXR Custom Shop La Machine Review, Premier Guitar, 2014-09-15
