The Xotic "Voltage Double" is a step-up converter that takes 9 volts DC and boosts it to an output voltage of 15 or 18 VDC (max current draw 80mA). Higher voltage levels result in more headroom. When you boost the voltage your find your Xotic pedals will get much more dynamic, more headroom, top end and brightness, less compressed sound. Boosting the Bass BB Preamp and Bass RC Booster sound great with bass guitar with the extra headroom and clarity. Simply plug in the power adapter to your existing power source, switch the voltage to either 15 or 18 volts and plug into your pedal. Delivers clean, consistent power with the lowest possible noise.