11993-01 We offer high-headroom, low-noise, 2-band and 3-band active onboard EQ preamps for use with both active and passive pickups. Each active bass preamp comes with high-quality potentiometers on a pre-wired harness, battery clip, and knurled black dome-style knobs. (volume/slap switch, blend, and concentric bass and treble controls for STC-2P and STC-2A) or four control knobs (STC-3A and STC-3P) and a single 9v battery in the control cavity. Two 9v batteries can be wired together in series for added headroom. We include all necessary mounting hardware: high-quality potentiometers on a pre-wired harness, battery clip, and knurled black dome-style knobs.