Abstract: A high-efficiency audio power amplifier featuring a tracking power-supply and an active noise shaping unit for reducing non-linearly and audible noise. Several variations of an non-inductive switched-capacitor tracking power-supply are presented, which are well-suited to integrated-circuit implementation and battery operation, and which provide an efficient power supply for the output stage over a wide range of voltages that can exceed the voltage limits of the main power source. The output of the tracking power-supply can be fed into an analog power stage, or can be used as a Multi-Level Quantizer for generating the output directly. A feedback and noise shaping allows the use of low-cost components while relaxing design constraints. Some simple switching strategies are disclosed which offer power efficiencies in excess of 80%.