Born as an experiment, this lysergic effect pedal escaped the lab to infect the musical consciousness.

Brad Plunkett didn’t set out to invent the sound of his generation. In 1965, his overlords at Thomas Organ Company asked him to shave four bucks off the price of an amp by replacing its expensive equalizer switch with a cheap potentiometer—a knob that varies voltage by changing resistance. The sound of Plunkett’s hack closely resembled the wah-wah of a muted trumpet. His bosses were unexpectedly pleased. Plunkett mounted his invention in a hands-free organ pedal so players could make their instrument emote by rocking their foot back and forth. Mad genius Frank Zappa got one, then he told Jimi Hendrix about it. Hendrix used it on Electric Ladyland’s “Burning of the Midnight Lamp,” making the wah-wah pedal synonymous with psychedelia. Five decades later, the wah-wah is sold by dozens of companies and has become a mainstay of everyone from Jimmy Page (“Dazed and Confused”) to Doug Martsch of Built to Spill (“Happiness”). It even caught on with trumpeters: When Miles Davis went electric, he also went wah-wah. $199