The Klon Centaur is a guitar overdrive pedal developed by Bill Finnegan between 1990 and 1994. The pedals were made manually by Finnegan. The Centaur is characterized as a "transparent" overdrive, meaning it adds gain to the signal without significantly altering the tone of the guitar.
About 8,000 units were built between 1994 and 2009. Guitarists praised the clear, uncolored tone of the boosted signal. The circuit had unique characteristics, most noticeably the use of an IC MAX1044 voltage converter. The voltage converter drives 18 volts to the operational amplifier which is the core of the circuit; at this voltage the response of the amplifier is different from at 9 volt, since its slew rate depends on the voltage supply. The higher the voltage supply, the higher the order of harmonics the operational amplifier will generate, and the more "metallic" the sound.
Depending on the settings of the control knobs, the pedal can act mostly as a clean boost, adding mostly volume and minimal coloring to the sound. This can be used to drive the input valve stage of the amplifier to use the characteristic distortion sound of an overdriven guitar amp. Alternatively (or additionally) the controls can be set to distort the sound signal in the pedal, where two germanium diodes can perform waveform clipping (see clipping (audio)). The "gain" knob is a double potentiometer (a "dual-ganged gain pot"), which controls the balance between the diode clipping stage and the clean stage. The two signals are summed together before they interact with the other two controls, treble and volume.
The circuit boards of Centaurs are notably "gooped", or covered with black epoxy resin in order to make it harder for imitators to replicate it.
After manufacture was discontinued, original units have been spotted exceeding $5000.00 USD and were considered rare collector's items. A number of pedal manufacturers have since come out with much more affordable products, some of which come very close to the characteristics of the Centaur. Still, the original Centaur is often used as a standard to compare new overdrive pedal designs.
In 2014, Finnegan sold the same effect under the name "KTR". The KTR features the same circuit as the original pedal, with the same germanium diodes at the heart of the sound-shaping circuit, but uses surface-mount technology, making the pedal compatible with mass production and smaller in size. Screen printed on the front of the KTR are the words "kindly remember that the ridiculous hype that offends so many is not of my making", in response to the cult following garnered by the original Centaur.
Among the guitarists who use the Klon Centaur are: Mark Tremonti, Jeff Beck, Warren Haynes, Britt Daniel (Spoon), Nick Valensi (The Strokes; CRX) John Mayer, David Grissom, and Adam Hann (The 1975). Nels Cline of Wilco once said, describing his Klon "...It's an amp in a box. No more worries in the world of 'amp du jour' about overdrive tone. It will be OK. The Centaur will take care of it..." Thaddeus Hogarth, a guitar professor at Berklee College of Music, describes the tone of the Klon as "dynamic...[it] works in combination with your guitar sound..."
- Jeff Beck
- Mark Tremonti
- Aaron Dessner
- Lzzy Hale
- Andy Summers
- Keith Urban
- John Mayer
- Black Francis
- Peter Frampton
- Warren Haynes
- Mike McCready
- Stone Gossard
- Nels Cline
- Lee Ranaldo
- James Hetfield
- Britt Daniel
- Joe Bonamassa
- Joe Perry
- Trey Anastasio
- Philip Sayce
- Nick Valensi
- Jason Isbell
- Mike Ness
- Josh Klinghoffer
- Dave Welsh
- Dean Wareham
- Yannis Philippakis
- Wooden Shjips (Erik 'Ripley' Johnson) 
- Noel Gallagher
- "Builder Profile: Klon's Bill Finnegan". Premier Guitar, West Warren, January 21, 2014.
- 25 Top Blues Songs. Hal Leonard. 1 July 2014. pp. 19–. ISBN 978-1-4950-0101-7.
- Dave Hunter (15 May 2013). 365 Guitars, Amps & Effects You Must Play: The Most Sublime, Bizarre and Outrageous Gear Ever. Voyageur Press. pp. 245–. ISBN 978-0-7603-4366-1.
- Guitar World Presents 200 Stompbox Reviews. Harris Publications. 1 June 2014. pp. 27–. ISBN 978-1-4803-9847-4.
- "Best Effects Pedals 2014: SonicState Gear Of The Year Awards". Amped 30-Dec-14
- http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/a741p3.html Op Amp Slew Rate: Tutorial; Formula; Calculator
- Is it good to have a higher slew rate? What are some of the effects due to slew rate limitations?
- Eric Jacobs (guitar amplifier designer) personal communication https://www.jakeamps.com.ar/
- "The Cult of Klon". reverb.com. 2014-01-22. Retrieved 2019-10-15.
- "Tone Bakery Creme Brulee Review". Premier Guitar, Charles Saufley, February 05, 2015
- "J Rockett Archer review". Music Radar.
- "the Cult of Klon". By Phillip Dodge Tone Report, January 23, 2014
- Mitch Gallagher (14 May 2014). Guitar Tone: Pursuing the Ultimate Guitar Sound. Course Technology. pp. 271–. ISBN 978-1-4354-5621-1.
- "Guitar Pedals". Austin Chronicle, Tim Stegall, February 6, 2015
- Hogarth, Thaddeus. "The Klon Centaur Phenomenon". Berklee Online. Berklee Online. Retrieved December 3, 2015.
- "John Mayer's Klon Centaur Professional Overdrive Guitar Pedal". EquipBoard 30-Dec-18
- "Nels Cline's Klon Centaur Professional Overdrive Guitar Pedal". EquipBoard 30-Dec-18