The Sadowsky Onboard Bass Preamp (4-Knob System) is a completely prewired system offering the same controls and the same legendary active preamp as all Sadowsky basses. This preamp is designed for installation on most J-style basses with a metal control plate. On newer active J-style basses with a side jack and a battery compartment, usually no modification is required. On passive basses, the only required modification is to move the output jack to the side of the instrument and to make room for a battery. The controls are: Volume – Pan (Balance) – VTC (Vintage Tone Control) – Treble / Bass. The treble and bass controls are boost only - flat response is with the controls at their complete counterclockwise position. The VTC control is passive, the maximum setting is a flat EQ. The further you turn the control down, the more the high end in the signal will be attenuated. The preamp can be installed either with the included control plate or mounted through a rear control cavity in either a 4-in-line or diamond pattern. This system is not compatible with active pickups requiring anything else than a 250K or 500K volume or balance pot.