A charge pump power supply for an audio power amplifier integrated circuit has an operating mode selected according to an indication of operating environment and/or a process position of the integrated circuit. The operating mode selects the output voltage provided by the charge pump and may also select efficiency by selecting a frequency of operation of the charge pump and/or the effective size of a switching transistor bank. The selection is made in conformity with an indication of a process position of the integrated circuit and/or an indication of an environment of the integrated circuit, such as temperature, power supply voltage and/or load impedance values, and generally also in conformity with a volume (gain) setting, or a detected signal level, so that internal power consumption of the amplifier and charge pump is reduced when a high signal level is not being reproduced at the audio power stage.