Effect pedal, Bass Preamp. The Bass BB Preamp distortion booster was designed to retain the original attack sound and tonal spectrums and produce a variety of gain structures for all bass players. Each of the two broadly-overlapping EQs offers 15dB of Boost or Cut. The gain knob offers pristine clean boost to a hard overdriven distortion which is very nice tone that stays firm, with great note separation and just the right amount of compression for a smooth overall texture. True bypass for eliminating any signal interference when switched off. Can be used with AC adaptor (optional) or 9V Battery.