The Fairfield Circuitry 20% More Limiting Distortion is a distortion pedal from Canadian maker Fairfield Circuitry, released in September 20251. Where a conventional distortion pedal clips the signal with diodes or transistors, this one is built around a slew limiter: a circuit that controls how fast the signal's voltage is allowed to change, normally found in modular synthesizers shaping control voltages12. The result, as Delicious Audio puts it, is a circuit that "acts as a dynamic low-pass filter, distorting audio in unpredictable, organic ways"1.
Guitar Pedal X's Stefan Karlsson described the outcome as "a sort of Distorted Low Pass Filter, with elements of wave folding," and traced the project back to its origin: "This project started out as a study into a mysterious old schematic - which looked suspiciously similar to a data sheet" square/triangle oscillator3. Fairfield Circuitry's own product page sums up the feature set as "jfet clipping, sub and upper octaves, envelope follower, low pass gate; impressions, ideas, pleasures and pains"4.
A slew limiter used as a distortion
Most distortion pedals get their sound by clipping: they chop the peaks off the waveform. The 20% More takes a different route. RockBoard's PedalPedia entry explains that "instead of normal distortion clipping stages, it applies a slew limiter to control how fast voltage changes"2. A slew limiter caps the rate of change of a signal, so fast transients, pick attacks, string snap, get rounded off or smeared, and the circuit distorts and filters as a side effect of that rounding.
Delicious Audio's Paolo De Gregorio notes that "at its core is a slew limiter, a circuit typically used in modular synths to shape control voltages," and that here it "acts as a dynamic low-pass filter, distorting audio in unpredictable, organic ways"1. The pedal also carries JFET clipping alongside the slew circuit, plus pseudo-wavefolding according to RockBoard42.
What that means for a player is a wide tonal range rather than one fixed voicing. RockBoard describes "a wide palette from quirky distortion to synth-like fuzz and filtering effects"2, and Delicious Audio reports that its switches and knobs together produce "everything from dynamic, envelope-sensitive fuzz to synth-like tonal mutations," including "synth-like growls, velcro-fuzz chaos"1. Guitar Pedal X heard "a cool somewhat clangy distortion voicing"3.
Controls
Guitar Pedal X lists the control set as follows3:
| Control | What it does |
|---|---|
| Volume | Output level |
| Blend | Mixes dry and effected signal |
| Input | Input level, which the pedal responds to dynamically |
| Low Pass Gate | Sets the low-pass gate behavior |
| Feedback | Feedback amount |
| Slew | How aggressively the pedal clamps down on fast signal changes |
| Envelope | Selects LPG or FEED behavior |
| Octave Up | On/Off |
| Octave Down | On/Off |
The Slew control is the heart of the pedal. Delicious Audio explains that it "adjusts how aggressively the pedal clamps down on fast signal changes, creating anything from smooth saturation to gated, splattery decay"1. The pedal also has a CV input for slew limiter frequency3, expression control, internal trim pots, and a sensitivity to input volume, which Delicious Audio says makes it "a pedal that rewards experimentation"1.
Fairfield Circuitry's product page lists the 20% More as sold out as of 25 October 20264. When Guitar Pedal X covered it in April 2025 it was in wide international distribution3, so secondhand and remaining dealer stock may still be found.
Relation to the Roger That
Guitar Pedal X places the 20% More alongside Fairfield Circuitry's Roger That, calling it "of a similar ilk to the Roger That - in being a unique and different style of distortion"3. The two pedals share an unconventional approach but not a circuit. The Roger That is described by Fairfield Circuitry as a "volatile and unpredictable distortion" built as an "RFI/EMI approximator"5, and Delicious Audio explains its core: "The core of Roger That is a simple JFET preamp, but by then including an FM modulator and demodulator circuit," the pedal imitates radio interference6. The 20% More instead uses the slew limiter as its engine12.
The Roger That also has a control-voltage connection: its Tune parameter has a 1/8" CV input "to be externally controlled by modular synthesizers or other control voltage sources"6, a design idea the 20% More carries forward with its own CV input for slew limiter frequency3.
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Questions
What is a slew limiter in a guitar pedal?
A slew limiter is a circuit that controls how fast a signal's voltage is allowed to change. It is normally found in modular synthesizers, where it shapes control voltages. Instead of clipping the signal the way a normal distortion stage does, a slew limiter rounds off fast transients, which produces distortion and filtering effects of its own.
Does the 20% More Limiting Distortion have an expression input?
Yes. Delicious Audio notes that the pedal has expression control, along with internal trim pots and a sensitivity to input volume, and describes it as a pedal that rewards experimentation. Guitar Pedal X also lists a CV input for slew limiter frequency.
Is the 20% More Limiting Distortion a fuzz or a distortion?
It sits between the two. Delicious Audio calls it an unorthodox take on fuzz that blends synth-inspired circuitry with guitar-friendly mayhem, while RockBoard describes a wide palette running from quirky distortion to synth-like fuzz and filtering effects. Guitar Pedal X files it as a distorted low-pass filter with wave-folding elements.
Is the 20% More still available?
As of late October 2026 the Fairfield Circuitry product page lists the pedal as sold out. When Guitar Pedal X covered it in April 2025 it was in wide international distribution, priced at 389 CAD, about 270 USD, on the Fairfield Circuitry webstore and 299 GBP at Andertons.
Does it have a CV input?
Yes. Guitar Pedal X lists a CV input for slew limiter frequency, which lets an external control voltage source, such as a modular synthesizer, modulate that parameter.
Is the Fairfield Circuitry 20% More Slew Limiting Distortion related to the Roger That?
Guitar Pedal X describes the 20% More as being of a similar ilk to the Roger That, in being a unique and different style of distortion. The two are distinct circuits: the Roger That is built on an FM modulation and demodulation scheme around a JFET preamp, while the 20% More uses a slew limiter.
Sources (6)
- Fairfield Circuitry 20% More Limiting Distortion, Delicious Audio, 2025-09-10
- 20% More by Fairfield Circuitry, RockBoard PedalPedia, 2026
- Guitar Pedal X, Guitar Pedal X, 2025-04-03
- 20% More, Fairfield Circuitry
- Roger That, Fairfield Circuitry
- Fairfield Circuitry Roger That RF Distortion, Delicious Audio, 2024-07-03
