A true class AB amp should consiat not only of a current amplifier (the push pull stage) but also a class A stage (the mosfet). The way class AB amps work is that for small signals (when the output does not reach the maximum peak power) the class A part works in the linear part of its characteristic providing low distortion and only little power drawn because it only amplifies signals below a certain threshold.,whereas a class B amp would only add crossover distortion at lower levels. Once the power rises beyond a certain threshold the push pull amp kicks in and relieves the class A amp. These amps often have efficiency levels of around 50%.
3.2W (average drawn) for 1.65W in 4ohms so around 50% efficiency.
