Mu-Tron III

Beigel was an engineer out of MIT. In 1970 Al Dronge, the president of Guild Guitars, bought the rights to a synthesizer Beigel had designed with a few MIT friends. It was like a Moog, Beigel said, “but a little different.”

Then Dronge was killed when his plane crashed. The accounts don’t agree on the year. The company’s vice president, an accountant, killed the synthesizer, and not one was ever produced.

Beigel and Aaron Newman, Guild’s former chief engineer, salvaged a piece of it. They thought about a ring modulator but decided it was a little too strange for the mainstream. Instead they took a section of the synth they called the “timbre generator,” added one of its four filters, and made an envelope follower. Newman’s version: “We made the first prototype of what became the Mu-Tron III envelope follower in the summer of 1972, and I left my job to start Musitronics.”

At first it was called the Auto-Wah. An investor came up with the name Mu-tron. The “III” came from Beigel’s fondness for the number three.

Here’s the idea. A wah pedal sweeps a filter when you rock your foot. The Mu-Tron III sweeps it when you play. Hit a note hard and the filter jumps open; let it ring and it closes again. Inside, an envelope follower reads your picking and drives the filter through little light-sensitive parts called optocouplers.

Beigel picked a filter that could do three jobs, low-pass, band-pass and high-pass, and put it on three switches with two knobs. Peak sets how sharp the quack is. Gain sets how much your playing moves it. It ran on two 9-volt batteries, and Beigel had a reason: “That way you could really smash on the guitar and not distort the whole effect.”

The case was designed with help from a man who had once led the team that styled the ’50s Studebaker. “We designed them so you could drop them off tall buildings and they’d still work,” Beigel said. The old ads promised it would work on almost anything: guitar, keyboards, drums, flute, sax. “The sharper your attack and the more percussive your instrument, the wilder your sounds.”

The first ones went to E.U. Wurlitzer in Boston, and soon Musitronics was making more, in a converted chicken coop in Rosemont, New Jersey. With 35 people on the payroll, it soon became the town’s biggest employer.

Then came “Higher Ground.” Wonder agreed to appear on a poster for the Mu-Tron III, and he came out to play some music with the team and talk. The song, Beigel said, put Musitronics “on the map.” “Soon all kinds of rock and roll and jazz players were using the unit.”

Frank Zappa was one. Asked in 1977 what wah he used, he answered, “I have a Mu-tron.” On “Stink-Foot” he played an acoustic guitar with two pickups, one into its own channel and the magnetic one into the Mu-tron and another channel, “so you have a sharp attack and an enveloped attack.” Jerry Garcia made it part of his signature lead sound with the Grateful Dead, and by 1978 he favored it alongside an MXR Distortion+. Bootsy Collins made its watery thump so much his own that one profile put it next to Eddie Van Halen’s Phase 90 and Hendrix’s Uni-Vibe. Musitronics even hired a young Larry Coryell to record a Mu-Tron III demo album, released in 1975.

Some of its best moments, notice, aren’t guitar at all.

Musitronics didn’t last. “Our downfall was the Gizmotron,” Newman said, a later product of theirs. ARP, the synthesizer company, bought Musitronics in 1978 or 1979, moved production to Lexington, Massachusetts, and went bankrupt a little over a year later. The Mu-Tron III went with it.

Beigel kept working on the sound. In 1996 he designed the Q-Tron envelope filters for Electro-Harmonix. In 2014 his new company released the Tru-Tron 3X, and he only let it out after checking it against two original Mu-Tron IIIs of his own. Four years later he got the Mu-Tron name back. He died in 2026, at 77.

He never pretended he’d seen it coming. He knew he’d built an automatic wah. He just couldn’t hear in advance what a real musician would do with it. “Higher Ground,” he said, was “something I had hoped for but couldn’t myself conceive.”

It took a man patting a Clavinet to show him what his box was for.