Designed for electric guitarists, the Pro Co Sound Fat Rat is a distortion pedal that builds upon the design of the original, well-regarded Rat by adding a switchable mosfet/germanium clipping circuit. So, with the flick of a switch, you can effect the original rat tone, or get the more scooped, smooth, and amp-like tone of the mosfet/germanium clipping section. You'll also note the Fat switch, which offers a bass boost and high cut at the same time, tailoring the pedal for lower tunings or bass guitars. 
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\r\nBesides the two aforementioned switches, the Fat Rat gives you a Distortion knob, a filter knob, an overall volume control, and a bypass/engage footswitch. A 1/4' instrument input and output are offered for your guitar, and the pedal is powered by a separately-available 9V battery through an easy-to-open battery compartment. It can also run off a 9V power adapter or an 18V power adapter, both of which are available separately.