Guitar Clean Boost pedal effect. The No. 2 is KHDK's original Clean Boost, utilizing the strength of KHDK's unique circuit. Providing a warm, tube-like boost, it was designed for those who appreciate a natural and subtle gain. Best used as a tool for shaping your tone on a quality all-tube amp, the No. 2 allows the organic and transparent EQ controls to fully develop your tone. Controls: Gain, Volume, Hi/Lo switch, Bass, Treble. The KHDK No. 2 Clean Boost is powered by a single 9V battery. You can access the battery connection by unscrewing the bottom plate of the pedal enclosure. Alternatively, plug in an external 9V DC (center negative) power supply. True Bypass.