Designed to be used with passive pickups, this version of our Tone Circuits will add a tremendous amount of on-board tonal versatility to any bass with 2 passive pickups. Our design enables players to boost or cut specifically focused frequencies in order to achieve signature tones and to dial in a great sound no matter what the situation. The STC-3PSB provides bass and treble controls, a midrange control, a master volume, a blend control, and our special frequency contour switch. This preamp was voiced by Steve Bailey to have three bands of focused EQ, together with a switch that engages a frequency contour optimized to bring out fretless harmonics as well as mid-range boost. The frequency contour is engaged by pulling up of the volume control. We even added two small trim pots on the circuit board can be tweaked to preset the frequency contour EQ just the way you want.The STC-3PSB Tone Circuit will work in any fretless bass that has space for 4 control knobs (volumefreq switch, blend, concentric bass and treble, and midrange controls) 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 pre-wired harness; battery clip; and black anodized, knurled, dome-style knobs.