The History of the Wah Pedal — From Clyde McCoy to Kirk Hammett

The wah pedal is rock's greatest accident. Not in the romantic sense of a happy mistake, but in the literal engineering sense: nobody sat down to invent it. Nobody had a vision of a foot-rocked filter sweeping across the midrange of an electric guitar. What they had was a junior engineer at a California organ company trying to replace an expensive three-position switch with a cheaper potentiometer — and the sound that came out when somebody plugged in a guitar changed the trajectory of popular music. The suits who ran the company thought it was for trumpet players. They were spectacularly wrong, and the guitar world has been rocking that treadle ever since.

The story of the wah touches nearly every corner of modern guitar culture. It begins in a corporate engineering lab in 1966. It runs through Jimi Hendrix's feet at Woodstock, through the funk sessions that defined Motown's twilight era, through David Gilmour's slow expressionist sweeps on Wish You Were Here, and ends — or rather continues indefinitely — with Kirk Hammett standing on a Cry Baby (Reverb) during every Metallica solo, daring anyone to tell him to stop. Nobody should. The wah pedal is the most human-sounding effect ever bolted to a pedalboard, and its history is inseparable from the history of what it means to make a guitar talk.

The Accident in the Lab

In 1966, Warwick Electronics — which owned the Thomas Organ Company — had a licensing deal with Britain's Jennings Musical Instruments to distribute Vox products in the United States. The arrangement gave Thomas the right to manufacture its own line of solid-state Vox amplifiers for the American market, including the 100-watt Vox Super Beatle. That amp had a mid-range resonant boost circuit built in as a featured effect. The British original used a three-position toggle switch to control it. Thomas needed something cheaper. They assigned the problem to Brad Plunkett, a 25-year-old junior engineer.

Plunkett bread-boarded a transistorized version of the mid-range boost, working from a circuit suggested by a colleague named Les Kushner. To test it, he connected a guitar and started sweeping the potentiometer by hand. The result was a resonant peak climbing and falling across the midrange frequencies — a vocal, crying sound that nobody in the room had heard before from a guitar. Plunkett later described people running in from adjacent rooms to find out what was making the noise. The question then became how a guitarist would actually operate this thing. Both Plunkett and Vox session guitarist Del Casher later claimed credit for the solution: strip the circuit out of the amp, stuff it into a Vox Continental Organ volume pedal enclosure, and let the guitarist rock it with a foot. By late 1966, the prototype existed.

What happened next reveals everything about how the music industry works. Thomas Organ president Joe Benaron heard the prototype and declared it unsuitable for electric guitar. He was a big-band devotee, and the sweeping resonant quality of the new effect reminded him of trumpet players using Harmon mutes — specifically, the style made famous by a jazz bandleader named Clyde McCoy on his 1930s recording of “Sugar Blues.” Benaron wanted to market the device to brass players. Del Casher pushed back. The suits at Thomas won the first round. Casher made a joke about naming it the “McCoy” after the trumpet player — and Benaron took it seriously. Thomas contacted Clyde McCoy, who was still alive, and offered him $500 to license his name and portrait for the new pedal. McCoy accepted. In February 1967, the first commercially available wah pedal hit the market under the name the Vox Clyde McCoy Wah-Wah Pedal — with McCoy's portrait painted on the base plate.

Clyde McCoy (1903–1990) was a real trumpet player, a genuine jazz figure, and, as far as anyone knows, had never played a guitar pedal in his life. He certainly never used the one that bore his face. The Vox Clyde McCoy is therefore almost certainly the first-ever artist-signature guitar pedal in history — endorsed by an artist who played a completely different instrument. The patent for the wah-wah pedal circuit was filed on February 24, 1967, and granted as U.S. Patent 3,530,224 on September 22, 1970. By then, the world had already moved on without it.

From Brass to Guitar: The First Adopters

Del Casher had always known this was a guitar effect. Frustrated by Thomas management's insistence on marketing toward brass players, he took the prototype to his studio in the Hollywood Hills and cut a promotional demonstration record on a budget so thin that Vox gave him money for a plastic-coated cardboard disc instead of actual vinyl. The demo reached musicians, and the right ones heard it. Meanwhile, the early production Clyde McCoy units were making their way into guitar players' hands through music stores in New York and elsewhere. Jimi Hendrix picked one up in 1967. Eric Clapton purchased one at Manny's Music on 48th Street in Manhattan during sessions for Cream's second album.

Clapton's use was the first public breakthrough for the pedal in a rock context. The track “Tales of Brave Ulysses,” recorded in May 1967 and released on Disraeli Gears, introduced the wah's swooping, expressive voice to a rock audience that had never heard anything like it. Clapton rocked the pedal rhythmically, in time with the tempo, using it as a textural element rather than a solo effect. It demonstrated that the wah wasn't a party trick — it was an instrument in itself. Meanwhile, Hendrix was simultaneously developing a completely different relationship with the pedal. His first recorded use appeared on “Burning of the Midnight Lamp,” a 1967 single from the Axis: Bold as Love sessions. But his defining statement came in 1968.

Thomas Organ soon wanted the pedal branded under their own name for the American market. Late 1967 saw the introduction of the Cry Baby, manufactured initially by an Italian company called Elettronica Musicale Europea (EME). The Cry Baby had the same circuit as the Clyde McCoy but a different enclosure — the early “Top-Logo” version had a slimmer, rounded case with the logo mounted on top. By around 1969, Jen Elettronica had taken over Cry Baby production and was running it independently, while the Vox line continued under the V846 designation. The patent sat there. The knockoffs multiplied. Thomas decided enforcing the patent was more expensive than ignoring the competition, and so the wah circuit became effectively open-source before “open-source” was a concept anyone used.

Jimi Hendrix and the Vocabulary of Wah

If Clapton showed what the wah could do as a rhythm device, Hendrix showed what it could do as a language. His favorite wah was an Italian-made Vox — almost certainly one of the early Clyde McCoy or Cry Baby units from EME — and his technician Roger Mayer would customize the potentiometer values and tapers based on Hendrix's specific preferences. Mayer reportedly noted that Hendrix's footwear even affected the sound: high heels produced more treble emphasis, while flat-soled sneakers gave a flatter frequency response. That level of attention to a pedal's mechanics tells you how seriously Hendrix took the instrument.

“Voodoo Child (Slight Return),” the closing track on 1968's Electric Ladyland, is the Rosetta Stone of wah technique. It begins with deadened strings struck rhythmically while the pedal rocks alongside — Hendrix inventing the core syntax of funk guitar almost incidentally, while a film crew waited around for footage. By striking muted strings while operating the wah in time, he converted the guitar into a percussion instrument that also had pitch and timbre. The “whiplash” opening provided a blueprint for twenty years of funk and R&B guitar playing that followed. Then the band crashes in, and Hendrix plays wah-driven lead lines over crushing power chords — using the pedal expressively, melodically, treating the treadle as a second voice overlaid on everything his picking hand was doing. “The wah-wah pedal is great because it doesn't have any notes,” Hendrix said of the effect. “Nothing but hitting it straight up using the vibrato and then the drums come through and that there feels like that, not depression, but that loneliness and that frustration and the yearning for something. Like something is reaching out.”

That emotional precision is the key to why the wah pedal transcended its era. Technically, it is a bandpass filter: it sweeps a resonant peak up and down in frequency, emphasizing a narrow band of the midrange while attenuating everything else. The standard GCB-95 (Reverb) sweeps a resonant peak from roughly 450 Hz up to 1.6 kHz as you push the pedal forward. Those are the frequencies that dominate human speech — the formants that differentiate vowels, the resonances that carry the emotional character of a voice. When a guitar passes through a wah pedal, it is borrowing the acoustic properties of the human vocal tract. No other guitar effect does that. It is why the wah sounds, at its best, like someone talking.

Funk's Secret Weapon

While rock was treating the wah as a lead guitar tool, funk and soul musicians were discovering something else entirely: that a wah pedal rocked rhythmically against muted or choked strings could function as the most powerful percussive element in a groove. The most famous early example is Charles “Skip” Pitts' guitar part on Isaac Hayes's “Theme from Shaft” in 1971. That sixteenth-note wah pattern — the relentless, machine-like “wacka-wacka” of muted strings through a rocking treadle — became one of the most recognized sounds in the history of recorded music. It used the wah not as an expressive device for solos but as a rhythmic engine, a one-man horn section playing in the pocket. The effect caught the attention of every session guitarist working in soul and funk at the time. One of them was Melvin Ragin.

Ragin, who earned the nickname Wah Wah Watson, had joined the Funk Brothers — Motown Records' studio band — in 1968. He had come across the wah pedal through fellow Funk Brothers guitarist Dennis Coffey, whose wah work on the Temptations' 1968 psychedelic soul classic “Cloud Nine” was one of the first prominent Motown uses of the effect. But Watson pushed the pedal far beyond basic rhythm use. On the Temptations' Grammy-winning “Papa Was a Rollin' Stone” (1972), Watson used the Cry Baby to build textures that shifted between percussive rhythm work, tonal coloration, and melodic punctuation across twelve minutes of cinematic soul. His session credits across the 1970s read like a survey of the era's greatest records: Marvin Gaye's “Let's Get It On,” Michael Jackson's Off the Wall, Quincy Jones' “Body Heat,” Rose Royce's “Car Wash.” Watson literally built his career and his nickname around the Cry Baby. No one before or since has used the wah with more rhythmic sophistication.

Dunlop Takes the Throne

By the late 1970s, the wah market was fragmented. Thomas Organ, Morley, and a scattering of Italian manufacturers were all producing variants of the circuit. The original Cry Baby name had passed through several hands after Jen Elettronica's production run, and the components used in different batches varied wildly — which is why players from that era will argue endlessly about which specific unit sounds best. In 1982, Jim Dunlop Manufacturing acquired all the original tooling and machinery used by Thomas Organ Company and Jen Elettronica when they manufactured the earliest Cry Baby pedals. They then introduced the GCB-95 Cry Baby, which became the standard-issue wah pedal for the next four decades. Dunlop standardized what the earlier manufacturers had left inconsistent: they scrutinized every component, from the potentiometer to the inductor, and built quality controls that meant one GCB-95 sounded like another GCB-95.

The GCB-95 is not a vintage recreation — Dunlop's engineers raised the frequency center and sharpened the wah effect compared to the darker, more subtle original Italian units, producing what the company calls a more “modern” voicing. Whether that tradeoff is worth it depends on what you want from a wah. Players who prefer the vintage sound often gravitate toward the GCB-95F Classic, which uses a Fasel inductor — the Italian-made toroidal coil that gives older units much of their characteristic warmth and “growl” — and rolls back the frequency center toward the original spec. The Dunlop 535Q Multi-Wah, introduced in 1994, offered six selectable frequency ranges and a variable Q control, effectively letting players dial in anything from a vintage Clyde McCoy voicing to a sharp, aggressive modern sweep. Dunlop has been making wahs longer than any other company, and their catalog of signature models — from the Jimi Hendrix JH-1 to the Slash SC-95 to the Dimebag Darrell DB-01 — reflects how completely the wah became embedded in guitarist identity across every genre.

Heavy Metal's Most Divisive Pedal

Rock had always used the wah — Jimmy Page on “Whole Lotta Love,” David Gilmour's slow expressionist bends, Slash's bluesy sweep on “Sweet Child O' Mine” — but heavy metal developed the most complicated relationship with it. In metal, the wah became a signature solo device: a way to add vocal articulation to fast runs that would otherwise blur into an undifferentiated wash of gain. Dialing in high-gain distortion and then stomping on a wah produced a nasal, honking midrange emphasis that cut through dense arrangements and made individual notes within a solo legible to the listener. It was expressive, it was aggressive, and it was immediately identifiable. Kirk Hammett heard all of that and leaned in harder than anyone.

Hammett's wah use across Metallica's catalog — from the accelerating fury of …And Justice for Allthrough the arena-filling anthems of the Black Album and beyond — became one of the most discussed stylistic choices in metal guitar. His signature Dunlop KH-95 Cry Baby (Reverb) reproduces the exact EQ, volume, and tone settings he dials in on his Cry Baby rack unit on tour — an extended midrange and a full heel-to-toe sweep designed for high-gain environments. The internet, predictably, has made Hammett's wah obsession a meme. Even Lou Reed weighed in during the recording of the LuLucollaboration: Hammett recalled Reed walking up to the microphone during a rehearsal where the wah was set up and saying, flatly, “Noooooo. No guitar solos. No wah-wah.”

Hammett has always been unapologetic. He admitted to Guitar World that his wah use grew organically out of the …And Justice for Alltour — stepping on the pedal during lead breaks for fun, then finding it stuck. He has also clarified that he never writes solos with the wah engaged; he composes them dry, then decides afterward whether the pedal adds something. “The wah enables me to mirror the inner voice in my head and in my heart,” he told Guitar World. “All these manipulated notes and tones, because that's what the human voice is like. We cycle through all these different tones and frequencies when we speak.” That is not the statement of someone mindlessly stomping on a pedal. That is a guitarist articulating, accurately, what makes the wah different from every other effect in the signal chain. The wah is a vocal instrument. Kirk Hammett understands that better than his critics do.

The Inductor Question and the Boutique Era

Once Dunlop standardized the Cry Baby, the boutique pedal world responded by differentiating on the one component that most affects a wah's character: the inductor. The inductor is a coil of insulated wire at the heart of the wah's bandpass filter circuit. Different inductors shift the pedal's resonant character — the precise shape of the frequency peak, its “Q” or sharpness, the amount of vocal quality versus nasal honk the pedal produces. The original Italian-made Fasel toroidal inductor, used in the earliest Vox and Cry Baby units manufactured at EME, became the object of obsessive pursuit among collectors and tone-chasers. Dunlop introduced the Fasel into the GCB-95F Classic in 2003, and the boutique market exploded with wah variants using Fasel replicas, custom-wound coils, and hand-matched components designed to approximate a specific vintage pedal.

Companies like Real McCoy Custom, Fulltone, and Xotic built their wah reputations on superior inductor quality and closer adherence to the original circuit topology. The wah modifier community — players who buy a GCB-95 and immediately replace the inductor, swap the potentiometer, and bypass the input buffer — rivals the Tube Screamer modifier scene for obsessiveness. This is a direct consequence of the wah circuit's simplicity: unlike a multi-stage distortion pedal with dozens of components interacting, the wah has a small number of critical parts, and changing any one of them produces an audible, identifiable difference in the sweep character. There is no other pedal category where the difference between a $25 inductor swap and a stock unit is more immediately obvious.

Why the Wah Is Impossible to Replace

Digital technology has replicated almost every analog guitar effect to the point where the gap between a software simulation and the original circuit is, for most practical purposes, inaudible. Reverb, delay, chorus, flanger, phaser — all of these have digital equivalents that most listeners cannot distinguish from the real thing in a blind test. The wah is different. Not because the circuit is too complex to model digitally — it isn't, it is one of the simplest circuits in effects pedal history — but because the wah's expressive quality depends entirely on the physical interaction between a player's foot and a mechanical potentiometer. The resistance changes unevenly as the wah rocks. The taper of the pot determines where in the sweep range the pedal is most sensitive to foot movement. The inductor's impedance interacts with the guitar pickup's output differently depending on pickup type and cable length. These variables are not bugs; they are the instrument. They are why a wah in skilled hands sounds alive in a way that an auto-wah envelope filter — however sophisticated — does not.

From Brad Plunkett's accidental potentiometer sweep in a Thomas Organ Company lab to Kirk Hammett rocking a rack-mounted Cry Baby at stadium volume, the wah pedal has spent nearly sixty years being declared a gimmick and proving everyone wrong. Clapton used one and wrote a psychedelic classic. Hendrix used one and defined the vocabulary of funk guitar. Wah Wah Watson built an entire career around it and played on more than 150 number-one records. Jimmy Page used one on some of the heaviest riffs in rock history. Hammett used one and polarized the metal internet. The effect has never been more or less than what it always was: the closest thing to a human voice that a guitar can produce. That is not an accident worth being embarrassed about. It is the most important accident in the history of the electric guitar.

If you want to hear what the wah sounds like at the peak of its powers, start with “Voodoo Child (Slight Return)” and sit with those first eight bars before the band enters. Then go to “Papa Was a Rollin' Stone” and listen to how Watson turns the treadle into a rhythmic instrument. Then put on the Black Album and listen to how Hammett uses the wah to make a pentatonic lick feel like a personal statement. Three completely different musical approaches, three completely different genres, one circuit from 1966. That is the wah pedal. Go find one and use it without apology.

Explore more: The Complete History of the Big Muff Pi — Dunlop Cry Baby GCB-95 Review — Metallica Gear Deep Dive