About the Pre-Phase Preamp The Pre-Phase Preamp is a miniature, onboard preamp that provides volume control and a phase switch for Pure pickups. It provides truly astonishing sound quality in an extremely small and light-weight package! The addition of the phase switch is one of the most important tools for live sound amplification of any acoustic instrument. Your unplugged acoustic guitar resonates in a given phase. The amplified sound needs to match this phase! Out of phase sound feeds back, has phase cancellations on some notes, and sounds quacky and tinny overall. Phase problems cannot be sufficiently solved with EQ. Any amp/PA/effect-unit/preamp may or may not flip the phase, the only way to be sure that your guitar is in phase with the amp-sound is a phase switch in your signal chain!