Active bass preamp for passive pickups. High headroom, low-noise, 2-Band active onboard EQ preamp. Comes with prewired 3-knob harness. It adds a tremendous amount of on-board tonal versatility to any dual pickup bass. The STC-2P 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. 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. The two small trim pots on the circuit board can be tweaked to preset the slap contour EQ just the way you want. Single 9 V battery in the control cavity. Two 9 V batteries can be wired together in series for added headroom.