Active bass preamp for passive pickups. High headroom, low-noise, 3-Band active onboard EQ preamp designed for use with passive pickups. Comes with prewired 4-knob harness. The STC-3P Tone Circuit provides bass and treble controls, a master volume, a blend control, and our proprietary Slap Switch. The treble control can produce a wide ranging, extremely usable response that is brilliant, yet smooth without being brittle. Our midrange control can be used to just slightly remove excess midrange honk or to add sonic power that will really make solos jump out. The bass can be reduced to tighten up a boomy instrument, or it can be increased to add warmth and punch. The Slap Switch is a pushpull located on the volume control. Pulling up on the volume knob will engage the special EQ contour voiced specifically for slap playing. Single 9 V battery in the control cavity. Two 9 V batteries can be wired together in series for added headroom.