# Pro Co RAT

The Pro Co "The RAT" is a distortion pedal produced by Pro Co Sound. The original RAT was developed in the basement of Pro Co's Kalamazoo, Michigan facility in 1978. Numerous variations of the original RAT pedal are still being produced today; it has become one of best selling guitar effects boxes of all time, with some retailers placing it in their top-ten most-sold pedals.
The pedal has changed in appearance over the years, but its tone has remained largely the same. Pro Co has also introduced variations of the RAT, including the Turbo RAT and the You Dirty RAT, among others.

## History

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 what would become "The RAT" pedal. Burnham began work on his circuit as early as 1974, right around the same time hard clipping distortion circuits were starting to enter the market. While experimenting with his circuit however, he accidentally used the wrong value resistor to bias the operational amplifier, driving it into heavy distortion. "Opamp distortion" as it has come to be known was a completely novel idea at the time and, combined with the diode clipping section, allowed for much more aggressive distortion than was available at the time. Author Pagan Kennedy describes Burnham's invention as follows:
   "One day, as he was soldering parts, he picked up a resistor of the wrong size -this was his lucky mistake- and attached it to a circuit board. The machine began shrieking and moaning. And that's how he heard a new sound; it was beautiful, haunting, ugly, and full of soul. He immediately recognized this as a major discovery, and he built that sound into a distortion pedal he named the Rat. Attached to a guitar, the Rat turned every note into a blast of outrage".
In 1978, "The RAT", named because of the rat infested basement in which it was designed, was being built as a custom-order product. Only twelve of these pedals (including one prototype), commonly referred to as the "Bud Box" RAT, were produced. Each pedal was built in a standard project box, hand painted, and hand drilled. In 1979, 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. Between 1979 and 1980 there were several cosmetic changes to the pedal as Pro Co worked to source knobs and print the labels on the pedal, but the circuit remained largely unchanged. In 1981 the Rat saw its first circuit change. The tone control, which allowed the user to lower the volume of the treble frequencies as they turned it counterclockwise, was reversed to turn the treble down as the knob is turned clockwise. From an electrical standpoint, this change made no difference, but Joshua Scott of JHS Pedals suggests that user preference for turning effects knobs clockwise may have led users to judge the effect as too harsh.
In 1983, Pro Co switched to a smaller, U-shaped enclosure.Finally, in 1988, the RAT2 was introduced, which included an on/off LED that utilized a new "millenium bypass circuit", which has become the industry standard for pedal switching circuits. The screen printed labels were replaced with glow in the dark mylar. 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. In 2019 Pro Co switched to an industry standard PSA adapter from their 1/8" adapter. Despite the high number of Rats released throughout the years, the circuit has remained very similar to the original schematic.
Other models of RAT products include:
* R2DU (1984–1988)
* Juggernaut (original) (1979–1981)
* RAT2 (1988–present)
* Turbo RAT (1989–present)
* Vintage RAT Reissue (1991–2005)
* BRAT / Roadkill (1997–2001)
* Deucetone RAT (2002–present)
* Juggernaut (reissue) (2003–present)
* 25th Silver Anniversary RAT (2003)
* You Dirty RAT (2004–present)
* SOLO (2006–present)
* '85 Whiteface RAT Reissue (2010)
* FATRAT (2014–present)
* Lil' Rat (2021–present)

## Circuitry

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. All except the power supply directly interact with the guitar signal. The signal enters into the pedal, travels through a bandpass filter that filters out high and low frequency content from the signal.
It then moves on to the gain stage, which is based around a single opamp, 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 at a certain voltage level to produce hard clipping of the input waveform. At lower gain levels the distortion is produced entirely through the diodes, but at higher gain levels the opamp begins to distort as well. Originally, 1N914 diodes were used, which were later replaced with 1N4148 since RAT2. The 'Turbo RAT' pedal uses red LEDs for this purpose (red LEDs have about a twice as high forward voltage as the original silicon diodes), while the 'You Dirty RAT' pedal uses 1N34A germanium diodes (clipping at a much lower forward voltage).
The distortion stage is followed by a passive "reverse" tone filter and volume control.
This circuit has remained almost entirely untouched throughout the manufacture of the RAT and RAT2. Other versions of the RAT are near identical to the RAT2 except for changes to the clipping diodes, different enclosures, or the addition of new controls.

## Versions of the RAT
### Current product line

* RAT2 (Silicon clipping diodes)
* Lil' RAT (Identical to RAT2 except without battery box. Surface mount components instead of through-hole)
* Turbo RAT (Red LED clipping diodes)
* You Dirty RAT (Germanium clipping diodes)
* FAT RAT (Silicon / MOSFET / Germanium clipping diodes mode, 'Thick' switch (bass boost / treble cut), 9/18V and a swappable opamp)
* Deucetone RAT (Dual RAT (2-in-1) pedal (separate In / Out jacks per side), Side A Silicon / LED / Germanium clipping diodes mode, Side B Silicon / LED / Diode lift clipping diode mode)
* Juggernaut (Reissue version)

### Non-RAT moniker pedals currently produced by ProCo

* Solo (Three asymmetric clipping diode pairs modes (Hot / Melt / Burn), Scoop control (Midrange), Tone (instead of typical 'reverse' Filter tone control), Texas Instruments OP07DP opamp. The prototype was called "RATZO" and featured a center placed dual-gang pot for 'Tone' & 'Scoop' controls along with the 'Distortion' and 'Volume' controls in typical RAT fashion)

### Discontinued products

* "Bud Box" RAT (The original handbuilt RAT)
* "Big Box" RAT (Distinct big rectangular box pedal)
* Juggernaut (also called "Bass RAT") (Original version) (modified RAT circuit with 'Low Pass' filtering in place, Dual (2-in-1) RAT size enclosure, Right side: 'Mix' (between Drive / Clean ratio), Master Volume and on the Left side: Amount (Drive), Tone, Vol. The pedal also features an external effects loop)
* "Small Box" RAT (Bent steel U-shape enclosure)
* R2DU (19 inch rackmountable double RAT pedal, usable in cascade mode or dual channel)
* BRAT / Roadkill ('budget' USA-made RAT2 derivative circuit designed for Guitar Center including the Motorola LM308 opamp with LEDs in the negative-feedback loop. The front faceplate is two-sided with one 'BRAT' print side and on the other side a 'Roadkill' print. Note, this pedal is 9 V battery fed only)
* Vintage RAT Reissue (rectangular shaped "Big Box" reissue model)
* '85 Whiteface RAT Reissue (Limited run '10)

### Special Runs

* IKEBE 40th Anniversary RAT: Limited run of all-white, all-red, and all-yellow RAT made exclusively for the Japanese market.
* 25th year Silver Anniversary RAT: "Big Box" pedal in a distinct silver coloured stainless steel enclosure with the tagline "25 years of Grunge" (Limited anniversary model, handed out to select artists and technicians by Pro Co sound).

## Popular modifications to the RAT

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 mod will translate to a thicker (fuzz like) bass response at the expense of losing distortion. Another popular resistor swap is to swap the 1M Ω R1 and R2 resistors for 2MΩ, which allows for a higher input impedance to maintain the fidelity of the input signal.
* Toggle Switches: The Mightier Mouse mod involves a 3-way switch to select between RAT / RAT2 (clipping via silicon diodes), Turbo RAT (clipping via red LEDs), and FAT RAT (MOSFET clipping) modes. It also shows an alternative to the Ruetz RAT mod by using a potentiometer or trimpot to replace the resistor instead of cutting it out of the circuit.
* Diode Lift: Removing one of the two (asymmetric clipping) or both (pure opamp clipping) clipping diodes results in a volume boost with a crunchier tone.
* Chip Substitutions: The original RAT pedals featured the rare Motorola LM308 opamp, which is now quite expensive to acquire. Recent RAT2 pedals nowawadays feature the widely available Texas Instruments OP07DP. Other opamps that people try, include: the CA3130EZ (MOSFET-based), the NE5535A / NE5534AP (high slew rate, low noise), the LM741 (low drive) and finally the TL071 / TL081 (both BI-FET based). Many RAT modders install an opamp socket to enable easy swapping of opamps, which is similar to what people do with the Ibanez Tube Screamer circuit.
* 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 opamp chip and the single 100 pF cap.
* Power Jack: 2.1 mm (Roland / 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). This modification is not necessary on pedals made after 2019 as they already use a Boss-style adapter.

## Clones

Because of the RAT's popularity, numerous large and small pedal designers and manufacturers have attempted to replicate its sound as 'clones' or in new designs. Often the goal of these 'clones' is to capture the sound of vintage RATS at a more affordable price point. Many RAT clones allow users to switch between the different RAT circuits (Turbo, standard, etc.) or between eras (Whiteface, LM308 Chip, Big box...). The simplicity of the circuit has also made it popular among pedal-kit manufacturers for first-time builders. Some examples of RAT 'clones' are:
* JHS Pedals Pack Rat
* TC Electronic MAGUS
* Mooer Audio Black Secret
* Walrus Audio Iron Horse
* Electro-Harmonix Flatiron Fuzz
* [Sondery] Metal Distortion

## Notable users

* Ichirou Agata of Melt-Banana
* Jeff Beck
* Nuno Bettencourt
* Frank Black
* Nels Cline of Wilco
* Lawrence Chandler
* Kurt Cobain
* Graham Coxon
* Kevin Eubanks
* Bill Frisell
* David Gilmour
* Dave Grohl
* James Hetfield
* Krist Novoselic
* Joe Perry
* Ben Monder
* Kurt Rosenwinkel
* John Scofield
* Sonny Sharrock
* Andy Summers
* Alex Turner
* Thom Yorke
* Xan McCurdy of Cake
* Boris
* Rivers Cuomo
* Neil Halstead
* Mark Gardener
* Matt Hardy of Skinshed.