The MXR Phase 90 delivers the classic four-stage phasing sound with continuously variable speed control. The Phase 90 has a fixed regeneration level that adds intensity and sounds great on guitars and keyboards. Uses batteries or ECB03 power supply. The MXR Phase 90 has found its way into many of Eddie Van Halen's recordings, adding a shimmery velocity to lead passages or a more dramatic swoosh to muted strumming. This phaser is not just designed for guitars; it works well with bass, keyboards and even vocals and appears in all of these guises on Dweezil Zappa's Z album, 'Music For Pets', which hints it is flexible and hip.