[tdelahanty]

100% refers to the relationship of input signal to conduction of current in the output stage. A class-A amp's output will conduct for 360 degrees (the entirety) of the input signal. A class-B amp's output will conduct for only 180 degrees. Class AB is squarely between the two. The lower duty-cycle of class AB or B amp sections (halves) gives them time to cool down thus allowing higher average power. Any amp regardless of configuration will consume more current when the volume is increased.