Wikipedia
Wolfbox
The Wolfbox is the name for the original passive DI unit, direct box, or DI as invented in the late 1950s by Dr. Edward Wolfrum, PhD, alumnus engineer of Motown, Golden World Records, Terra-Shirma Studios, Metro-Audio Capstan Roller Remote recording, and United Sound Systems in Detroit, Michigan. Used by James Jamerson, Dennis Coffey, Bob Babbit and other The Funk Brothers, the Wolfbox was a key component in the 1960s and 1970s sound of recorded music in the Motown/Detroit scene.