In Stock. 45 Day Lowest Price - 100% Satisfaction Guarantee. The T-Rex Dr.Swamp is a double distortion pedal. It has that rich vintage sound, T-Rex is known for. Besides the warm crunchy sound, this pedal gives a lot of steady bottom. You can flip back and forth between the two gain settings A and B - by clicking switch A or B. The lid (A or B) is indicating the active gain. The pedal is turned off, by clicking the switch (A or B) that is lid.