Pro Co RAT

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Pro Co RAT2

The Pro Co "The RAT" is a guitar effects pedal produced by Pro Co Sound. The original RAT was developed in the basement of Pro Co's Kalamazoo, Michigan facility in 1978.[1] Numerous variations of the original RAT pedal are still being produced today.

The basic RAT has changed in appearance over the years, but its tone has remained largely the same. Pro Co has also introduced tonal variations of the RAT, including the Turbo RAT, and You Dirty RAT, among others.

The Pro Co RAT became very popular in the early 1980s, thanks in part to fame gained by its use by several artists.


The origins of the Pro Co "The RAT" can be traced back to the mid-1970s, when Pro Co engineers Scott Burnham and Steve Kiraly repaired and hot-rodded existing distortion pedals, such as the Dallas Arbiter Fuzz Face. Burnham decided he could build a superior product from the ground up, and designed "The RAT" pedal.

In 1978, "The RAT" was being built as a custom-order product. Only twelve of these pedals, commonly referred to as the “Bud Box" RAT, were produced. Each pedal was built in a standard project box, hand painted, and hand drilled. By 1979, as the pedal became more popular, Pro Co began mass-producing them. This iteration was built in a custom designed, rectangular sheet-metal enclosure, with an L shaped removable top/back section giving access to the internals. The top panel was labeled with Pro Co Sound "The RAT" and the three control knobs as Distortion, Tone and Volume.

In 1983, Pro Co switched to a smaller, U-shaped enclosure. Finally, in 1988, the RAT2 was introduced, which included an on/off LED. Various RAT2 circuit board layouts and wiring configurations have surfaced in the last few years, including the noted "RAT3 version A and B" all under the RAT2 moniker. The RAT2 model is still available today, but in 2008 production moved to China and is now manufactured by Neutrik for Pro Co Sound.

Other models of RAT products include:[2]

  • Juggernaut (1979)
  • R2DU (1984)
  • RAT2 (1988)
  • Turbo RAT (1989)
  • Vintage RAT (1991)
  • BRAT (1997)
  • Deucetone RAT (2002)
  • Juggernaut Bass RAT (2003)
  • You Dirty RAT (2004)
  • '85 Whiteface RAT Reissue (2010)


The Pro Co "The RAT" is a distortion pedal with a quite simple circuit, which can be broken down into four simpler blocks: distortion stage, tone control, output stage and power supply.[2]

The design is based around a single op-amp, originally the Motorola LM308 (switched to Texas Instruments OP07DP around 2002-2003). The distortion is produced using a variable gain circuit with diodes shorting the output to ground to produce hard clipping of the input waveform. Originally, 1N914 diodes were used, which were later replaced with 1N4148 since RAT2. Turbo RAT modification uses red LEDs for this purpose (red LEDs have about twice as big forward voltage, as original diodes), while the You Dirty RAT modification uses 1N34A germanium diodes.[2][3] The distortion stage is followed by a passive tone filter and volume control.

This scheme is similar to the Boss DS-1 distortion pedal, although there are major differences between the two circuits. A major difference is the opamp used, the LM308, known for its poor slew rate; it accounts for the sonic difference between the two pedals. The most popular RAT pedal, the RAT2, features true-bypass switching.

Versions of the RAT[edit]

Current product line[edit]

  • RAT 2 (Made in China)
  • Turbo RAT
  • Deucetone RAT
  • You Dirty RAT
  • Solo
  • Fat Rat

Discontinued products[edit]

  • '85 Whiteface RAT Reissue
  • "Bud Box" RAT
  • The RAT
  • Juggernaut
  • "Small Box" RAT
  • Vintage RAT
  • BRAT
  • Roadkill (same circuit as the BRAT with a different enclosure)
  • Juggernaut Bass RAT

Non-RAT pedals produced by Pro Co[edit]

  • Solo

Popular modifications to the RAT[edit]

The RAT is a popular pedal for modifying. Some of the possible modifications include:

  • Resistor Mods: The Ruetz RAT mod which involves simply cutting the 47 Ω resistor to disengage half of the drive circuit. Gain is reduced somewhat and the bass is no longer attenuated. Additionally, the 560 Ω resistor controlling the lower half of the distortion filter can receive similar treatment. Either can translate to thicker (fuzzier) bass response at the expense of less distortion.[4]
  • Toggle Switches: The Mightier Mouse mod involves a 3-way switch to select between RAT 2 (clipping via op-amp only), Turbo RAT (clipping via red LEDs), and MOSFET clipping modes. It also shows an alternative to the Ruetz RAT mod using a potentiometer or trimpot to replace the resistor instead of simply cutting it.[5]
  • Diode Removal: Removing one of the two silicon clipping diodes for a volume boost crunch tone.
  • Chip Substitutions: The original RAT pedals featured the LM308 op-amp which is now quite expensive. Recent RAT pedals now feature the Texas Instruments OP07DP. Other op-amps that people try include the CA3130EZ (MOSFET-based), NE5535A, NE5534AP, LM741 and TL071 (FET-based). Many install an IC socket to enable easy swapping of ICs, very much similar to what people do with the Ibanez Tube Screamer.
  • Capacitor Mods: "softening" ceramic caps replaced with silver mica or metal film caps for better tonal fidelity. These include the 30 pF cap riding the IC chip and the single 100 pF cap.
  • Power Adapter: 2.1 mm (Boss-style) 9 V DC adapter socket mod. Because the tip on the Boss-style adapter is negative, one needs to install a plastic 2.1 mm socket to avoid shorting out the barrel of the plug against the RAT's steel chassis. Note, the official website says it uses a positive tip adapter.
  • Robert Keeley does a popular mod involving replacement of the existing op-amp for an original LM308, a capacitor upgrade (using film and tantalum capacitors) to improve bass response and a 3 way mode switch. The first mode is the Classic RAT which is the original RAT circuit. The second mode is the Phat RAT which has an extra diode added to the original circuit in attempt to achieve a more tube-like sound. The final mode is the Mighty Mouse in which a diode is removed from the original circuit causing it to behave more like a boost pedal.[6]
  • Electronics modders Vodka Mods perform a popular RATsputin mod that includes dual toggle switches to the drive and clipping sections, a Texas Instruments NE5534AP op-amp upgrade and an extra case mounted potentiometer, which allows maximum control over tonal variables.[7]
  • Msm Workshop's ModeRAT mod includes a three-way clipping switch (RAT, Turbo RAT, booster mode), two-way gain switch, and a third switch to flip between a bright or normal setting. Offers original LM308 chip or metal can version.[8]

Notable users[edit]


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