Classic Gear: ProCo Rat

Since the late 1970s, distortion pedals have become a mainstay in most guitar players' gear arsenal. Many guitar pedals have come and gone since then, while some have remained as part of the fabric of guitar tone. One of those pedals is the ProCo Rat.

It's safe to say that the Rat has become one of the most recognisable guitar pedals of all time, used by countless big-name artists across a range of genres. Known for its aggressive tone which pairs perfectly with an overdriven amp, every guitar player should try a Rat at least once!

Image courtesy of Paul Reno

ProCo Rat history

The brand ProCo was born in 1974, when Charlie Wicks, a former employee of Kalamazoo business The Sound Factory, found himself without work when The Sound Factory closed its doors for the last time due to business hardship.

Charlie founded ProCo with the aim of making high quality speaker cabinets, cables and other pro audio gear, and the company quickly scaled and became known for the quality of products and second-to-none customer service.

Sometime around 1977/78, ProCo engineer and employee Scott Burnham designed the first Rat circuit, but it is theorised that early prototypes could have existed as early as the company's inception in 1974. 

The first official Rat pedal was build at some point in 1978. This was known as the Bud Box Rat, named after the manufacturer of the pedal's enclosure, Bud Industries. Despite 1978 being widely accepted as the first year of production, Scott has loaned a Bud Box Rat to the Kalamazoo museum which is dated to 1977.

There is a long-standing belief that, in the first year, Scott built 12 Bud Box Rat pedals, however Scott himself has refuted this claim. He confirms that he did make 12 circuits, but only 11 units were made – one pedal was fitted with two circuits as a "Double Rat" for guitarist Tom Taylor.

The Rat distortion style

The Rat pedal is known as a hard-clipping distortion. The overall tone of the pedal has a very distinct voice that is very aggressive, with lots of top end bite and a strong mid-range push. At more extreme settings, especially when stacked with other drives, it can take on a fuzz-like character.

The Rat's strong mid-range lends punch to the overall guitar sound and helps cut through the mix in a band situation. It's a great distortion to pair with an already overdriven amp, or to use as a lead boost to fatten up and help single note lines cut through.

Although ProCo has created a range of variations on the Rat pedal, the classic version is based around a single op-amp, where the distortion is created with a variable gain circuit that uses silicon diodes to short the pedal output to ground at specific voltage levels. This creates the hard clipping.

When run at lower levels, the pedal produces all its distortion from the diodes alone, but as you push the pedal, the op-amp also moves into distortion.

The Rat Filter control

One of the most useful features of the Rat is the Filter control, in lieu of a conventional tone control. On a typical guitar pedal, the tone control will add specific frequencies, but the Filter control on the Rat works in reverse, acting as a low-pass filter which cuts more high end as you turn the knob clockwise. 

This is useful to help tame excessively bright or harsh treble frequencies when pairing with different types of amps, guitars or pedals  – especially useful at stage volume.

Variations on the ProCo Rat

Since the pedal's inception, ProCo have created a several variations on the Rat. Some of the key versions are:

Rat2

The Rat2 is the modern equivalent of the classic Rat circuit and is the version that is most readily available today.

Lil' Rat

The Lil' Rat is essentially the same circuit design as the Rat2 but is half the size and doesn't include the battery box, so can only be run off a power supply. It also uses surface mount components instead of through-hole components.

Turbo Rat

The Turbo Rat is a modded Rat circuit that uses red LEDs for the clipping instead of silicon diodes, which gives the pedal a higher output and a little extra gain on tap.

You Dirty Rat

The You Dirty Rat is another modded variation of the classic Rat circuit that uses germanium diodes for the clipping instead of the silicon diodes of the original. The germanium diodes give the pedal a warmer sound with a heavily saturated, fuzz-like distortion character.

Popular Rat Mods

Alongside the multiple variants of the Rat available from ProCo, the circuit has become a popular design for modders who enjoy DIY projects. The Rat has a variety of different mods that can be performed, of ranging difficulties, to unlock different variations of the standard sound:

Resistor mods

A common modification is to add or remove different resistors to change the sound of the pedal. For instance, removing the 47Ω resistor will disengage half of the drive circuit and reduce the bass attenuation. You can also perform this mod by removing the 560Ω resistor for a similar result.

Another mod is to remove the 1Ω resistors in positions R1 and R2 and switch them for 2Ω resistors, giving the pedal a higher input impedance and higher fidelity sound.

Toggle switches

A more advanced modification is to add a toggle switch to change between different clipping diodes. This can give you the sound of the classic Rat (silicon) Turbo Rat (LED) and Fat Rat (MOSFET) in one pedal.

Diode lift

If you remove one, or both of the diodes you can get some different clipping options out of the Rat. Removing one diode will give you asymmetric clipping, while removing both will give you only op-amp clipping and will also provide a volume boost.

Chip swapping

As with many popular overdrive pedals, swapping the op-amp chips is a great, and relatively inexpensive way, to try different mods. Original Rat pedals came with a Motorola LM308 chip, which was changed to the Texas Instruments OP07DP in the Rat2. Other popular chips to try include CA3130EZ, NE5535A, NE5534AP, LM741, TL071 and TL081.

Shop Rat-type pedals at Boost Guitar Pedals

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As well as various Clipping and Op-Amp modes, the Drunk Beaver Heavy Bat features per-channel Volume controls, a Distortion control and a Blend control which is especially useful for retaining some of your clean signal when playing bass or down-tuned riffing. It's one of the most complete Rat-type pedals out there!
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The Drunk Beaver Bat Cold War V2 is a mutant Rat circuit, using NOS US-made LM308 and NOS Soviet UD1408B op-amps as well as 6 different clipping modes to give 36 different iterations, enabling you to dial in your perfect Rat sound!
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The mighty sounding Russian Plague stacks a modified Turbo Rat circuit Into a 1992 "Civil War" Muff – or vice-versa. It can conjure up some huge, crushing sounds when both channels are operated together.
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Influenced by the raucous Proco Rat, the Lichtlaerm Audio .Ritual. was born following a customer request for a pedal that captured the sound of Post-Metal band, Amenra, who gave their official seal of approval to the project once they saw and heard the results. This is the newest version, featuring a sweepable Era mini-pot which takes you from classic "White Face" Rat to a Turbo Rat. There's even a separate Boost, which offers a significant +35dB of output, adjusted via a 3-way toggle to act as a full-range boost, mid-boost, or treble-boost. Nice!
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ProCo Rat alternatives

While original Rats fetch big money on the resale market, the modern equivalent, the Rat2, is still a big seller in many guitar stores. Over the years, a variety of Rat-style pedals has emerged which capture that magic of the ProCo Rat.

JHS Pedals Pack Rat

The JHS Pack Rat is a one-stop shop for Rat fans, with a 9-way selector switch that allows you to select between 9 different classic circuits ranging from the original late-1970s sound to modern mods.

TC Electronics MAGUS

This is a great, affordable variation on the Rat circuit. TC Electronics chose to replicate the LM308 op-amp-era Rat but included a mode switch to allow you to switch between classic, Turbo and Fat modes.

Tate FX Sirens Scream

If you're looking for a more boutique take on the RAT, this pedal from Tate FX gives you 3 different takes on the Rat in one pedal. The 3-way toggle switch allows you to choose silicon, LED or no clipping diodes.

Notable Rat users

The Rat has become one of the most popular distortion pedals of all time and it's no surprise that in that time it has found its way into the rigs of many well known players. Here are a few notable users of the Rat:

• Jeff Beck
• Nuno Bettencourt
• Kurt Cobain
• Graham Coxon
• David Gilmour
• Dave Grohl
• James Hetfield
• Joe Perry
• Krist Novoselic
• Andy Summers
• Thom Yorke
• Rivers Cuomo
• Alex Turner