MAXON SM-9 PRO+ distortionThe SM9Pro+ was developed based on the distortion core of the Maxon SM9 (Super Metal 9), which was used a lot in the late 1970s. It creates scooped heavy metal tones with high level gain circuitry and cut midrange circuitry. It operates under 9V but an internal switch can be set at 18V, increasing dynamic headroom, stabilizing high quality sound and reducing significantly all background noise.