Power amplifier efficiency confusion
An old nutmeg..
The DC power into a class A amplifier is voltage x current. Now, if the current is a DC quiescent value superimposed with an AC value (representing the signal) you might think that DC voltage x AC current might factor into things. Well, it doesn't and what you find is that the DC power in is DC voltage in x DC current in. Where the DC current in is the average value of the DC current.
In other words, for a class A amplifier, no matter what signal you have as your input (within reason of course), the DC power taken by the amplifier is constant.
If you overdrive the input and get a nasty distorted waveform shape out then all bets are off.