Pro Co RAT Distortion

The Pro Co RAT Distortion is a distortion pedal made by Pro Co, built around a single op-amp gain stage followed by diode clipping. Aion FX describes it as "a distortion pedal with a very distinctive and tight mid-to-high-gain character that made it a staple in the rigs of 1980s hard rock bands"¹. Guitar.com's reviewer notes that while the consensus is that it is a distortion, it can also do overdrive and fuzz².

The signal path is simple: your guitar signal hits an op-amp and is amplified to a degree decided by the Distortion control, and the clipping diodes then shape that amplified signal into distortion². GuitarPlayer's Dave Hunter calls the RAT, released in 1979, "usually considered the seminal heavy distortion pedal"³.

A tight, mid-to-high-gain distortion

The RAT's character comes from its hard-clipping design. Guitar World's review of the Lil' Rat, which uses the same circuit, classifies it as a "hard clipping distortion"¹⁰, and Guitar World's history of the pedal describes Pro Co's design as "their own distinctive take of an op-amp-based distortion circuit combined with diode clipping"¹¹.

What that means in practice is a wide gain range. Guitar.com's Cillian Breathnach found that "at low gain, high volume and filter to taste there's not an insignificant amount of tight, bright articulate distortion"², while MusicRadar's review of the Lil' Rat describes how the Distortion control "dials in the gain, with that fur coat coming on at extreme settings"⁸. At high Distortion settings the RAT moves into fuzz territory².

The pedal also works as a boost. In Sweetwater's demo video, Don Carr showed it driving an already distorted amp: "now i'm going to use it as a boost for an already distorted amp so i'll turn the distortion down on a little rat"¹².

Guitar World's beginner pedal guide sums up the RAT 2's strengths and its one dividing point: "Powerful, punchy distortion", good at low-gain or high-gain settings and very affordable, though the guide notes some players might not like the timbre of the distortion⁴.

The controls

The standard RAT has three knobs: Distortion, Filter and Volume⁸⁹. Later versions add more.

The Filter knob is the control that catches most players out, because it works backwards from a normal tone control. Guitar World's history explains: "This control works 'backwards', with the 'zero' setting providing full treble that becomes darker and warmer as you turn" the knob up¹¹. TONEHOME's page for the RAT version 2 says the same: "The Filter cuts high frequencies as it is turned clockwise"¹³.

EarthQuaker Devices' beginner guide to pedalboards, covering the RAT, praises this control: "The Filter knob (sometimes referred to as the Tone knob) has a great sweep, allowing you to precisely dial in your distortion to cut through or sit back in any mix"¹⁵.

The circuit and where it came from

The RAT's design is based on the LM308 single op-amp⁶, with the same basic topology as an earlier pedal: Aion FX considers the RAT "an evolution of the MXR Distortion+", with "the same basic op-amp gain stage followed by diode-to-ground clipping"¹.

The RAT's own circuit has gone on to seed other designs. Aion FX's analysis of the Expandora found that "it's clear that the Expandora circuit originated from an experiment in putting two RAT Distortion pedals in series"¹⁶. EarthQuaker Devices' Sunn O))) Life Pedal, reviewed by Guitar World, also feeds its signal "into a vintage white-logo Rat distortion-style circuit"¹⁷. Third-party makers have built RAT-style pedals of their own, such as the Spürr Audio Wild Rat Distortion, which "takes the legendary Proco RAT basics and gives it a wild twist"¹⁸.

From the first RAT to RAT2, Turbo RAT and other versions

The release date depends on who you read. Aion FX and Delicious Audio give 1978 as the first release¹¹⁹; Guitar.com and GuitarPlayer give 1979 as the first production model, designed in the mid-1970s²³; Guitar World splits the difference, describing a pedal "developed in 1978, and mass produced from 1979 onwards" with "a decent claim to being the first proper mass-produced" distortion pedal¹¹⁹².

From there the RAT went through many iterations:

• RAT2: the updated version, with Distortion, Filter, Volume and Mode controls on the current model²⁰
• Turbo RAT: a famous variant using LED diode clipping²¹
• You Dirty RAT: another tweak on the classic design²²
• Lil' Rat: roughly half the size of the most recent RAT, with the same circuit and components as the RAT 2²³
• FAT RAT: a 2014 update with a FAT switch that "provides significant low end boost"²⁴²²²⁵
• RAT Distortion SOLO: four knobs plus a 3-way selector, with a Scoop knob as a mid-tone shaper and glow in the dark graphics¹⁴
• Vintage RAT (1991 to 2005) and Small Box RAT (1988): earlier enclosure changes tracked by TONEHOME²⁶²⁷

Pedal of the Day's review of the RAT2 notes that "Pro Co have introduced several varieties of the RAT over the decades, such as the Turbo Rat, and You Dirty Rat"²², and Performer Mag adds that the RAT "has been released in many versions over the years that each have their own characteristic distortion tones"²⁸.

The FAT RAT follows "previous tweaks on the classic design, including Turbo RAT and You Dirty RAT", according to MusicRadar's NAMM 2014 coverage²⁵. Pedal of the Day called the FATRAT "the 'RAT on steroids'" and found that "this thing wails, but isn't too harsh like many distortions"²⁴.

What reviewers said

Guitar.com's Josh Gardner, in the site's 60 Seconds video review, opens bluntly: "The ProCo RAT is an all-time classic distortion that needs no introduction"²⁹.

MusicRadar's best distortion pedals guide lists the RAT 2's "unique distortion character" among its plus points³⁰, and Guitar World's beginner guide highlights its "powerful, punchy distortion" and affordability⁴.

In Premier Guitar's demo of the Lil' Rat, the presenters walk through the controls, noting that "our filter knob works in reverse"³¹.

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In Sweetwater's video, Don Carr demonstrates the Lil' Rat's range, from low-gain settings into its use as a boost in front of an already distorted amp¹².

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Videos

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