Joyo JF-21 Splinter

The Joyo JF-21 Splinter is a distortion pedal from Chinese maker Joyo, released in early December 2021¹. It is built as a clone of the ProCo Fat Rat, carrying over the classic RAT control set and the Fat Rat's two toggle switches, at what Delicious Audio called "an extremely affordable" price². Joyo describes the pedal's voice as "an interesting combination of fuzz and distortion," with tones that shift between the two as you turn the knobs³.

For a player, that means one box covers ground from a thick, saturated distortion to edgier, fuzz-flavored grind. The RAT family it descends from has been a staple of distortion boards since the original design, and the Fat Rat variant that the Splinter copies added switchable modes to that circuit⁴.

A RAT-style distortion with fuzz-like tones

Joyo's own description of the Splinter leans on the fuzz-distortion hybrid character. The product page says you "get the unique tones that resemble both fuzz and distortion by adjusting the DISTORTION, FILTER & VOLUME knobs"³. Delicious Audio repeats that framing, calling it a stompbox that "recreates the sound of the FAT RAT, with all the same exact options as the original"².

The three knobs are the classic RAT set:

Because the Filter knob is reversed compared with most tone controls, turning it clockwise darkens the sound and counter-clockwise brightens it. That is inherited straight from the RAT layout the pedal copies².

A Fat Rat clone with four modes

The Splinter's circuit follows the ProCo Fat Rat, a variant ProCo introduced at NAMM 2014 as one of its tweaks on the classic RAT design, alongside the Turbo RAT and You Dirty RAT⁴. Gearnews reported the Splinter's release in December 2021 as a budget Fat Rat clone¹, and its writer's assessment of the circuit was direct:

Joyo also carried over the Fat Rat's two toggle switches⁵, which give the pedal its four operating modes⁵:

• Stock: the standard RAT-style voicing
• Fat: a thicker, bassier take on the circuit
• Mosfet: a clipping variation using mosfet transistors
• Fat + Mosfet: both modifications engaged together

Gearnews lists the four modes as "stock and fat, as well as stock and mosfet," matching the two-toggle layout of the original⁵. For context on what the fat modification adds, Jack Orman's technical analysis of the Fat Rat mod on the AMZ Guitar Effects Blog found the modified RAT "can now do clean boost, blues drive and full tilt boogie," meaning the switch widens the pedal's usable range rather than just adding low end⁶.

The name is part of the same RAT lineage. Gearnews notes "the name points to the rat connotation, and is taken from the character in the Teenage Mutant Ninja Turtle comics" of the 1980s: Splinter, the rat mentor of the Turtles⁵.

Power and connections

The Splinter runs on a single 9V DC supply with a center negative plug, drawing 20mA³. That is a light draw, so it will sit happily on most multi-output pedalboard supplies.

Connections are simple: a 1/4" mono input jack with 1M Ohms input impedance and a 1/4" mono output jack with 100 Ohms output impedance³. The high input impedance means the pedal presents a friendly load for guitar pickups, and the low output impedance lets it drive long cable runs or the next pedal in the chain without tone loss. The box measures 120mm deep by 97mm wide by 55mm high and weighs 390g, a standard compact-pedal footprint³. An owner's manual is included as the listed accessory³.

Where it sits among Joyo's distortions

Joyo's distortion lineup spans several circuits, from the high-gain R-17 Dark Flame to the multi-mode R-11 Baatsin. The Splinter sits in the range as the company's take on the Fat Rat, a circuit it recreates with the same exact options as the original². Where other Joyo distortions chase amp tones or multi-mode clipping, the Splinter is built around that single classic circuit, with its DISTORTION, FILTER and VOLUME knobs shaping tones that resemble both fuzz and distortion²³.

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