The Mud Killer adds some new features to the classic Tube Screamer circuit. The gain can be switched out, so it can be used as a colored clean boost. It can be set up for one channel use on multi channel amps. There is a bass cut knob to trim off excess low end. There are two types of gain available on Comp switch. Great pedal but I'm not enough of a TS fan to keep it. Powered by AC only. Sorry, didn't keep the box. New sells for $199, selling for $120 or trade for a delay, EHX Bender Royale, Way Huge Havalina or Klon clone. No Mooer, Joyo or other cheap crap. No shipping, pickup in Chicago ONLY.