There is only one knob and it controls the overall output. Just plug in and rock. 

The CB Overdrive can accept any good quality 9vDC adapter for use with audio circuits that is filtered and regulated with a center-negative tipped plug.

Susumu Tamura of Maxon designed the go-to overdrive unit back in 1979, a little green number with which you may be familiar. Since then, the circuit has been refined over and over again, but the earliest person to hit it big with a total rework of the device was a man named John Landgraff. His "Dynamic Overdrive" overhauled the typical green overdrive topology and changed the circuit for the better. Our Overdrive takes Landgraff's inspiration in kind, tailoring the classic circuit into a dead-simple specimen that lets you turn on and rock out.