When using a two button footswitch with my Coliseum 880 head the left switch turns the distortion on/off and the right switch turns the boost on/off. The head has a slider switch on the front under the distortion knob that will turn the distortion on/off without a footswitch but there is no similar switch on the front of the head for the boost so until I acquired a footswitch I could not activate the boost feature. The two switches appear to work independently so you can activate the distortion with or without the boost or you can activate the boost with or without the distortion.
