Maxon 9-Series Vintage Overdrive Pro Switchable 9V or 18V operationReacts to picking dynamicsTrue-bypass This combination clean booster/overdrive features switchable 9 or 18 volt operation using an internal voltage doubler The VOP-9 Pedal reacts precisely to picking dynamics and also features true bypass switching Since their introduction in the early 1980's, Maxon 9-Series effect pedal designs have achieved a legendary, almost mythical status with pedal connoisseurs around the globe The reasons for this are simple--superior sound quality and innovative features that offer a seamless interface between performer and performance--nothing more, nothing less