ProCo Rat 2

The Pro Co RAT 2 is an analog distortion pedal and the current standard model of a circuit that dates back to 1978¹. It is best known for its widespread use in grunge, rock and punk in the 1990s², and Guitar.com's reviewer describes it as a pedal where "the consensus is that it is a distortion, but it can do overdrive and fuzz"³. At low gain settings, the same reviewer found it "evokes a cooking tube amp that's just starting to overdrive. It's a surprisingly dynamic and expressive sound"³.

The circuit is essentially the same as the first big-box RAT³, housed in a sturdy metal enclosure with a sloped front⁴. It runs on a 9V battery or a standard 9V pedal power supply, with an all-analog signal path and true bypass⁴¹.

Op-amp and diode clipping

The RAT is an op-amp hard-clipper. As Guitar.com explains it: "an op-amp is doing the 'making louder' bit" and the signal then hits the clipping stage, "a pair of 1N4148 silicon diodes" connected to ground³. The Distortion control sets how much the op-amp amplifies the signal; at higher settings, distortion occurs before the diodes³.

The op-amp itself is a big part of the RAT's story. Vintage units used the LM308 chip, which Guitar World credits with the pedal's unique sound, "internally clipping the signal into a triangular shape"⁹. The modern RAT 2 uses an OP07DP op-amp instead, a change made in the early 2000s¹⁰, and Guitar World calls the loss of the original chip "the only real drawback of the modern ProCo RAT"¹. On the DIY side, the Guitar FX Layouts blog puts it bluntly: "the Rat won't sound like a Rat without LM308"¹¹.

The Filter control is the RAT's tone knob, and it works in reverse of what many players expect: it cuts high frequencies as it is turned clockwise⁵. Among DIY builders it divides opinion. Mirosol, author of the Guitar FX Layouts RAT 2 layout, wrote: "The Filter control is something that i've hated on every Rat i've ever build," noting that swapping the pot for 50K or smaller makes it more usable¹¹.

The circuit also invites modification. Documented RAT mods include the Ruetz mod, which changes the 47R resistor to a pot for smoother overdrive, and diode swaps: red LEDs for a Turbo Rat style conversion, or 1N34A germanium diodes to make a You Dirty Rat¹¹. Builders in the layout's comments reported good results with LED clipping, one saying he replaced the diodes with blue LEDs and "it roars"¹¹.

History and versions

The RAT was developed in 1978 and mass produced from 1979 onwards, and Guitar World says it "has a decent claim to being the first proper mass-" produced distortion pedal¹. The second version of the big-box RAT, built from 1981 to 1983, switched the Tone control to the Filter control and changed the logo to a more stylized treatment with lower-case "a" and "t"⁵.

The RAT 2 itself was released in 1988⁶⁴. Its circuit is essentially the same as that first big-box RAT³¹¹. Pro Co has since introduced several varieties over the decades, such as the Turbo Rat and You Dirty Rat¹³. That Pedal Show identifies the RAT 2 as the "current standard model"¹⁴.

Kurt Cobain used a blend of his Pro Co RAT going straight into the Neve desk and his mic'd amp for "Territorial Pissings" on Nevermind⁶, and Gearnews writer Jef called it "my go-to pedal for about 30 odd years. I currently own 5 of them!"¹⁵.

What reviewers said

Published reviewers have been consistent about the RAT 2's build and versatility:

• MusicRadar: "Plenty of gain"⁶
• Delicious Audio: "The RAT2's construction is very sound"⁸
• Guitar.com: "It's very versatile, with everything from bright crunch to grungy pseudo-fuzz just a couple of knob-turns away"¹⁶
• Premier Guitar: "a bitchin' low-to-medium-high-gain distortion and overdrive, more likely to be seen at the feet of indie-rock guitar" players than metal players¹²
• GuitarPlayer's writers went as far as to say "every guitarist should own a ProCo Rat 2"¹⁷

Guitar World also notes Pro Co's five-year warranty, "even if you happen to abuse the poor thing so much it falls apart"¹⁸.

In Sweetwater's demo video, Mitch Gallagher and Shawn Wells walk through the pedal's range, opening with the observation that "Everybody knows the RAT pedal is an iconic pedal"¹⁹.

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Price and buying

Guitar World's 2026 buying guide puts the RAT 2 "around the $80 mark"¹. Premier Guitar noted in 2024 that the contemporary China-built version "sells for a whopping $70" and still gets you most of the way to the sound of a vintage unit⁷. Delicious Audio reviewed it at $79.95 in 2022⁸, while a retailer listed it at $119.99 in October 2026²⁰, so prices vary by seller. MusicRadar also references a £89 non-LM308 loaded RAT 2 in the UK market²¹.

Videos

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Questions