briefHistoryOfProCoRat banner

The RAT is born

Back in the olden days of late seventies, one Scott Burnham, bearing the title of Pro Co Sound Inc.’s “Hippie in Charge of Technology”, toiled away in a rat-infested basement of his employer’s facility in Kalamazoo, Michigan. And while the customers browsed the relatively unheard-of company’s various electric guitar accessories in the showroom above, Scott, like a true sonic alchemist, was on a sacred quest of distilling the pure essence of guitar distortion.

And although there were quite a few distortion pedals available at the time (bear in mind, this was happening when the members of Black Sabbath were already well-established as the kings of heavy music with countless other bands following suite), Scott wasn’t satisfied with what was already out there, and sought a pedal that would make a sound to fill up arenas with its hellish roar, a pedal with a sharp and nasty bite that would really make the hair on the back of your neck stand up.

During that time, countless attempts were made, but not one resulted in the effect that Scott desired, and Pro Co slowly began to feel disheartened with his project. However, as fate would have it, while working on yet another attempt to make One Pedal To Rule Them All, Scott accidentally attached a wrong resistor and attached it to the circuit board – and the effect it produced blew his mind.

Since its arrival on the electric guitar gear market, Pro Co’s RAT made an impact that shook the very foundations of rock. Countless musicians flocked to the pedal’s amazing distortion potential, and the RAT burrowed its way into the annals of rock and metal as bands such as Metallica, R.E.M., Aerosmith, Nirvana and many more began using it as a staple of their sound. But what does exactly Pro Co’s RAT pedal contain, and how did it change throughout the years? Let’s find out.

Reading the RAT’s entrails

The Rat soon became very sought after for its prodigious ability to provide both filthy distortion and very high sustain. Essentially, the RAT pedal uses two symmetrical diodes to ground after the gain stage, producing the final effect of a hard, square-wave clip. The first models used a LM308 op-amp with a slow response, which hard-clipped both the op-amp as well as high- frequency attenuation, resulting in the RAT’s signature aggressive distortion. The LM308 also has a strong impact on the EQ, by letting frequencies below 500Hz run wild, while clipping it off almost completely above 5kHz or so.

Traditionally, the RAT contains three knob controls for distortion, filter and volume. The pedal’s distortion is surprisingly versatile, since it shines on higher gain but remains reliable in low-gain settings as well.

The filter control represents your run-of-the-mill low-pass filter, which makes a square wave signal with decreased bass, while bringing the signal closer to a triangle shape with the bass flowing freely.

Finally, the volume control surprisingly doesn’t affect the tone due to a JFET buffer thrown in between the two circuit blocks, with the output block being a 100K pot that blends the signal. Now that we’re more familiar with the RAT’s guts, let’s go over a bit of history.

“Bud Box” RAT

Despite Scott Burnham’s amazement with this unique sound he accidentally came up with, during those early days in 1978 there were still serious doubts about if and how much the newly-born RAT would be commercially viable, and, as a result, it was never intended to be mass produced.

Going under the moniker “Bud Box”, only twelve of these original RATs were ever made. You could get one only on direct demand, and all were made by hand. The “Bud Box” came in a humble-looking black casing with the logos of Pro Co, the RAT pedal, and the name of its place of origin printed in bright florescent silk-screened font. The “Bud Box” contained all three iconic knobs, labeled “Distortion”, “Tone” (stand-in for EQ), and “Volume”.

The reason for apparently only twelve people wanting one could probably be found in the fact that this first incarnation of the RAT was kept firmly inside Pro Co Sound’s closet rather than in there being no interest for such a pedal – but rather the opposite; as we’ll see, everybody needed a RAT; they just didn’t know it yet.

The Rat

Apparently, Pro Co changed their opinion about this pedal’s commercial viability as early as 1979, and released “The Rat” into the vast wilderness of the wider guitar gear market. This iteration was mass produced from 1979 to 1981, and this was the time when “The Rat” became to take the world by storm.

Much better-looking than its predecessor, “The Rat” was cased in custom 20 gauge wrap-around enclosure that gave off an air of durability and extravagance. The three knobs retained their names, albeit in a much discrete print. The logos, now more elegantly designed but in the same silk-screened print, were enclosed in a neat little rectangle beneath the controls.

Although the RAT would more or less keep the same spirit throughout its various iteration, there’s one technical aspect of “The Rat” that stands out – namely, the “Tone” knob would increase high frequencies when turned clockwise, whereas the later models functioned the other way around.

The Rat (ver.2)

Pro Co Rat 2As the Rat fever was spreading through the music world, the pedal responsible for this mass infection went through yet another round of elegant streamlining of its design. The casing was now a gorgeous ink black, and the “Rat” logo switched its last two letters to lower case, fully embracing its name (if only for a little while).

The “Tone” knob was now titled “Filter”, and, as already mentioned, it would cut the high end the more it was turned clockwise. The Rat (ver.2) would have a relatively short run, from 1981 to 1983.

Small Box RAT

The iconic pedal’s fourth incarnation, the Small Box RAT (produced from 1984 to 1988) kept its predecessor’s circuitry fairly intact, and the changes introduced were mainly of cosmetic and practical nature.

The casing went to a more compact 12-gauge, U-shaped base, and the visuals got a clunky makeover that simply screamed ’80s. The pedal’s name got changed back to all capital letters, and it was now printed in black on a silk-screened rectangle alongside the Pro Co logo under the knobs.


If your first thought when reading the name was the endearing robot from the Star Wars franchise, you wouldn’t be far off the mark. Going beyond the similar name, R2DU resembled the beeping blue-white dome in being a clunky piece of electronics that provides practical solution nobody expects.

This iteration came in a time when rack effects were all the rage, and Pro Co of course followed suite. Simply put, R2DU was two RAT pedals jammed together in one rack space box. And while this may seem like a weird choice to someone who’s new to the world of distortion effects, such a pedal provides you with the options of either playing with a single RAT switched on, or engaging both to provide you with an even nastier distortion effect.

Pro Co made R2DU’s clunky nature even more practical by adding a RFS-2 dual footswitch which allowed the musician to control the pedal remotely.


The year 1988 was the next chapter of RAT pedals began. The RAT 2, which is commercially available even today, took design cues from the Small Box RAT and streamlined the clunkiness of the ’80s design. The RAT logo was the only one left on the pedal’s face, and it had a Lexan/Mylar overlay with glow-in-the-dark graphics, while Pro Co also introduced a red on/off LED so you know where you’re at while playing on a poorly-lit stage.

In 2003, another subtle cosmetic touch was added to the RAT 2 in the form of a sloped casing, which also graced the Turbo RAT from then on.

Turbo RAT

Turbo RatWhile 1988 was the year that heralded a new era of RAT pedals, 1989 was the year when big changes in practical effects were actually introduced – enter the Turbo RAT. As its name already suggests, the Turbo RAT was the first pedal to really spike up RAT’s biting force.

Although the circuitry remained largely the same, the important change came from the fact that Turbo RAT had different clipping diodes, resulting in a much nastier distortion. Turbo RAT has been available ever since its introduction, with the models from 2003 and onwards having a sloped face casing.

Vintage RAT

By 1991, the RAT pedal reach that point of fame where people began to feel nostalgic for its older models, which also coincided with beginnings of mass appreciation of all things vintage (and ’70s especially, when it comes to the world of rock music).

As a result, Pro Co decided it was prime time to re-issue the gorgeous “Rat” (with only “R” in capital), first introduced in 1979. The only two things that make the reissue different to the original are the lack of words “Sound Inc.” in the Pro Co logo and the easy access battery compartment on the pedal’s back.

The Vintage RAT was produced from 1991 to 2005.


Despite RAT’s ubiquitous fame, it was still an expensive piece of gear, and the Brat was there to bring the rat fever to the masses. Introduced in 1997 and produced until 2001, the Brat has a more fragile casing painted in pink, with the Brat logo scrawled aggressively on the pedal’s midsection. Also, the EQ knob’s name was changed back to “Tone”, like on those early models.

Deucetone RAT

Duecetone RatWhile the Brat served as the budget version, the Deucetone RAT, produced from 2002 onwards, served as the high-end, boutique version of the iconic pedal. Like the R2DU, the Deucetone RAT merged two RATs, but now in the form of a pedal. Furthermore, this version introduced “dirty” and “clean” settings, giving guitarists even more material to play with.

You Dirty RAT

You Dirty RatIt didn’t take long for Pro Co to realize they were onto something with the “dirty” and “clean” options introduced in the Deucetone RAT, and as the desire for ever harder distortion grew, You Dirty RAT was introduced in 2004 to meet that demand.

Despite not changing much in the ways of core circuitry and controls, You Dirty RAT had the “dirty” part integrated in the single-channel pedal. Another difference from the majority of the rat pack is the fact that You Dirty RAT has germanium clipping diodes, just like its cousin Turbo RAT.

Flight of the RAT

As we’ve seen, the RAT began its life as a humble labor of love and ended up being one of the most iconic and sought after pedals out there. Despite being based on a relatively simple premise, the rat’s distorting potential opened up a whole new vista for musicians looking to add a stronger bite to their sound, while also providing the gear industry a rock-solid foundation to build upon. And with so many iconic musicians owning their sound to the RAT and so many other pedals improving on its principle, it’s safe to say that the landscape of rock wouldn’t be the same without this filthy powerful rodent. Also, since the RAT has remained reliable through its numerous incarnation as it was in the beginning, it’s still a great pedal option for beginners and pros alike, and the RAT is sure to make your sound into a fever that will spread far and wide.