Pro Co RAT Distortion — Complete Guide
The Pro Co RAT is one of the most distinctive distortion pedals ever made. Available since 1978, it has been used by Jeff Beck, Dave Grohl, Kurt Cobain, Thom Yorke, Graham Coxon, James Hetfield, and Reb Beach across rock, alternative, metal, and post-rock contexts.
What sets the RAT apart from other distortion pedals is its unique Filter control — a low-pass filter that works in reverse of conventional Tone controls — and its LM308 op-amp clipping circuit that produces a warmer, smoother distortion character than the harder-clipping Boss DS-1 or similar pedals.
The RAT Signal Chain and What Makes It Distinctive
The RAT uses an LM308 op-amp (in vintage units) to drive the clipping section, producing asymmetric soft clipping that is warmer and more complex than the symmetric hard clipping of pedals like the Boss DS-1. The result is a smoother distortion that retains more of the guitar's natural harmonic character.
The circuit produces a relatively compressed, "vocal" distortion quality at moderate gain settings, and a more aggressive, high-gain character at higher Distortion settings. The tonal range spans from classic rock crunch to heavy metal — one of the widest ranges of any distortion pedal.
The Three Controls (and Why the Filter Is Backwards)
DISTORTION: The amount of gain and clipping. At low settings (1–4), the RAT is a light crunch or heavy overdrive. At medium settings (5–7), full rock distortion. At maximum (8–10), aggressive high-gain character. The RAT's gain range extends further into high-gain territory than the TS9/TS808 while remaining smoother than the DS-1.
FILTER: This is the most confusing control on the RAT because it works in reverse. Turning the Filter clockwise cuts high frequencies (makes the tone darker). Turning it counterclockwise retains more high frequencies (brighter). The knob acts like a bass-cut filter in reverse: fully counterclockwise = brightest, most treble; fully clockwise = darkest, most bass-heavy.
When you first use a RAT, set the Filter at 10 o'clock (counterclockwise from noon) for a neutral starting point. From there, dial clockwise (darker) if the tone is too bright or harsh; dial counterclockwise (brighter) if you need more cut.
VOLUME (or Level): Output volume. Set to match your bypassed signal level, then adjust to taste for boost.
Best Settings for Different Styles
Classic Rock / Blues Rock (Led Zeppelin feel)
- Distortion: 4–5
- Filter: 10 o'clock (slightly bright)
- Volume: 6
Low-to-medium Distortion, Filter slightly counterclockwise for brightness — the RAT at these settings produces a musical crunch with good note definition. It sounds closer to an overdrive than a heavy distortion, retaining picking dynamics.
Alternative Rock (Blur, Radiohead, Nirvana)
- Distortion: 6–7
- Filter: 11 o'clock (neutral to slightly bright)
- Volume: 6
Graham Coxon's RAT settings for Blur's guitar work — moderately high Distortion with a neutral Filter. This range gives full distortion without the compression of maximum Distortion settings.
Metal (Metallica entry-level, 80s hard rock)
- Distortion: 8–9
- Filter: 11 o'clock
- Volume: 5
High Distortion with Filter slightly counterclockwise to maintain treble clarity. At high Distortion the RAT becomes more compressed and harmonically dense — useful for heavier playing but the pick dynamics are significantly reduced.
Jeff Beck Lead Tone
- Distortion: 4–6
- Filter: 12 o'clock (noon — neutral)
- Volume: 6–7
Jeff Beck has used the RAT in his signal chain at moderate settings — it adds midrange warmth and controlled gain without extreme compression. His fingerplaying technique (no pick) means he relies on the pedal for sustain rather than raw gain.
Dark, Dense Rhythm (post-rock, shoegaze)
- Distortion: 7–8
- Filter: 3 o'clock (darker)
- Volume: 6
Filter turned clockwise for the dark, bass-heavy wall of distortion effect. The dense, rolled-off high end creates the "wall of sound" character associated with post-rock and shoegaze rhythm guitar. Needs high volume amp to fully develop.
Famous RAT Users
Jeff Beck
Beck has incorporated the RAT into various rigs throughout his career, using it for leads where he needed more controlled distortion than his amp alone provided. His fingerplaying technique means he looks for pedals that respond well to dynamics — the RAT's op-amp character does this better than many alternatives.
Kurt Cobain (Nirvana)
Cobain used the RAT alongside the DS-1 at various points. The RAT's smoother clipping character is audible on some Nirvana recordings as a warmer alternative to the DS-1's more aggressive sound.
Dave Grohl (Foo Fighters)
Grohl has used the RAT consistently in Foo Fighters recordings. Its warm, moderate-gain rock character suits the Foo Fighters' combination of melodic pop and guitar aggression.
Graham Coxon (Blur)
Coxon is one of the most dedicated RAT users in British rock — it appears throughout Blur's discography, particularly on the rawer, guitar-forward material from the mid-1990s.
Thom Yorke / Jonny Greenwood (Radiohead)
Radiohead have used the RAT as a distortion source on various records, consistent with their approach of combining conventional rock gear with unconventional applications.
RAT Versions: What Changed
The RAT has gone through several significant revisions since 1978:
Original "Flat Box" RAT (1978–1983)
The original circuit used the LM308 op-amp. Very limited production, extreme collector value. Not significantly different from the White Face version that followed.
White Face RAT (1983–1988)
Still using the LM308 op-amp. This is the "vintage RAT sound" that most players reference — warmer, more complex clipping character than modern versions.
RAT 2 (1988–present)
Added a LED clipping option (instead of, or in addition to, the standard clipping), changed the enclosure color (black), and later switched from the LM308 to the OP07DP op-amp in most versions. The OP07DP sounds slightly brighter and more aggressive than the LM308. The RAT 2 is the current standard production version.
LM308 vs. OP07DP: The LM308 has a lower slew rate, which produces a slightly slower, warmer clipping behavior. The OP07DP is faster and brighter. The difference is audible in direct comparison; in a live mix, both sound like "the RAT."
You Dirty RAT (YDR)
A current production version using LM308 op-amp components, specifically to replicate the vintage sound. More expensive than the standard RAT 2 but preferred by tone purists.
Turbo RAT
Adds a clipping diode switch for a more compressed, higher-gain character. The LED clipping option produces a brighter, tighter distortion. Useful for players who find the standard RAT too smooth at maximum Distortion.
RAT vs. Boss DS-1
These are the two most commonly compared budget distortion pedals:
Clipping character: The RAT uses softer, op-amp clipping that produces a warmer, more compressed tone. The DS-1 uses harder, asymmetric diode clipping that produces a more aggressive, brighter character.
Tone control direction: The RAT's Filter control works in reverse — clockwise = darker. The DS-1's Tone control works conventionally — clockwise = brighter. This is the most practically confusing difference for newcomers.
Midrange: The RAT has more natural midrange content than the DS-1. The DS-1 sounds more scooped and brighter at equivalent settings.
Best application: DS-1 into clean amp for alternative/grunge; RAT into clean amp for classic rock, jazz-influenced rock, or applications where you want a smoother, less aggressive distortion.
Frequently Asked Questions
How does the RAT Filter control work? The Filter is a low-pass filter that cuts high frequencies as you turn it clockwise — the opposite of a conventional Tone control. Counterclockwise = brighter (more treble retained). Clockwise = darker (high frequencies cut). Start at 10–11 o'clock and adjust from there.
What amp works best with the Pro Co RAT? Any clean amp works well. Fender Twin, Marshall JTM45 (at clean settings), Roland JC-120, Vox AC30 on clean. As with the DS-1, stacking the RAT into a high-gain amp usually produces muddy results — use one or the other.
Is the RAT good for metal? At high Distortion settings, yes for classic metal and 80s hard rock. For modern high-gain metal (death, djent, technical thrash), the RAT is not typically tight or aggressive enough — a dedicated high-gain amp or pedal (Mesa Boogie, EVH 5150) is preferred.
What's the difference between the RAT 2 and the original RAT? The RAT 2 uses an OP07DP op-amp in most versions (versus the LM308 in originals), which produces a slightly brighter, more aggressive character. The enclosure was changed from white to black. The core circuit is the same. The vintage LM308-based sound is available in the You Dirty RAT version.
Does the Pro Co RAT work with bass guitar? Better than many distortions because the Filter control can retain significant low-end when turned clockwise (dark position). The RAT is a recognized bass distortion pedal among bass players who want a grinding, controlled distortion without losing low-end weight.
Should I buy the RAT 2 or the original/vintage? The RAT 2 is the practical choice at $60–70 new. Vintage originals command $200–400+ for modest tonal differences. The You Dirty RAT is the best-of-both option if the LM308 character matters to you.