Sadowsky Onboard Preamp Assembly, onboard preamp kit for bass guitar, prewired, 4 control knobs, volume, balance, VTC (push-pull for active/passive) stacknob (bass / treble) power source : 1x 9V (ca 870h battery life) bass control +13dB @ 40Hz treble control +13dB @ 4kHz input inpedance 1MegOhm output inpedance 1kOhm, frequency response 5Hz - 50kHz,