Corrosion of Conformity guitarist Pepper Keenan has revealed what he believes is the secret behind AC/DC’s iconic guitar tone. He discussed the discovery in a conversation on the Garza Podcast.
Keenan explained that the tone comes from a piece of hidden gear tied to wireless guitar technology used by both AC/DC and Eddie Van Halen. He described how a compression component from those units was repurposed into a standalone device.
“The way I would describe it: it’s the guts of a wireless unit that AC/DC used back in the day…and Eddie Van Halen’s wireless unit was the same company,” Keenan said. “And they took the guts – not the wireless part but the compression part that the wireless units used – and they put it into one of those things.”
He went on to describe the distinct effect the device has on guitar tone once it’s added to a rig.
“So, it’s got this weird compression limiter thing you can put on it,” Keenan continued. “And when you add it, it sounds like once you have it on there and you turn it off, you’ll never turn it off again. It sounds like you’re taking a wool blanket off your cabinet. It’s hard to explain, but when you hear it, you’re like, ‘Oh’.”
Keenan also pointed to visual evidence of the device in Angus Young’s live setup. He also shared a specific studio anecdote about how it was rediscovered as the missing piece in Young’s tone.
“You’ll see photographs of Angus’ rig and all the amps stacked up. But you’ll see that thing shoved in the corner,” he said. “[AC/DC] recorded an album one time and I think Angus’s tone…he wasn’t happy with the tone. And they’re like, ‘What’s missing?’ And the only thing missing in his signal chain was his wireless unit. So, they went and got the wireless unit, plugged it in the studio, and bang, there it was. Because the wireless unit will compress a signal to try and get it to throw that far y’know?”
Keenan’s story lines up with decades of documented history surrounding Angus Young’s gear. The device he’s describing has a name: the Schaffer-Vega Diversity System.
Angus Young began using the Schaffer-Vega Diversity System in 1977, initially as a way to move freely on stage without a guitar cable. The unit, however, did far more than transmit a wireless signal. Its circuitry included a companding process that compressed the signal before expanding it back out. This process added boost, sustain, and harmonic coloration that became inseparable from AC/DC’s studio and live sound.
The same technology found its way into Eddie Van Halen’s rig during the same era. The Schaffer-Vega system was widely used across major rock acts in the late 1970s and early 1980s, including Ace Frehley of Kiss, the Rolling Stones, and Frank Zappa. Young and Van Halen, however, were the artists whose tones became most closely associated with the unit’s distinctive push.
Young himself confirmed the unit’s role in shaping his sound in decades-old interviews. He once stated plainly that the Schaffer-Vega was the only effect in his signal chain. He credited it directly for fattening up his tone on both rhythm and lead guitar tracks across multiple albums, including Back in Black.
Keenan’s account describes a band realizing their tone was missing something, only to discover it was the wireless unit itself. This mirrors the documented history of Young occasionally leaving the device out of his rig and immediately noticing the absence. The compression and preamp boost built into the system were never something AC/DC could easily replace with a standard pedal. That is why the unit remained a fixture of Young’s setup even after wireless technology evolved.
