Selects the desired amp model
Selects the desired speaker & cabinet type
Determines how hard you drive the input stage. The more drive, the more distortion.
Bass, Middle, Treble
EQ to sculpt our tone. High and low do what you would expect them to. The Middle control's operating frequency is selected with the Mid Freq switch which has five different positions.
Ultra Hi & Ultra Lo
Pushing Ultra Lo and Ultra Hi adds a boost to the respective frequency ranges and also causes a slight curve shift in the midrange.
This aptly names knob transparently compensates for any level changes your settings may have caused. Both Drive and Volume are controllable by CV.