A composite bridge amplifier having four output metal oxide semi-conductor field effect transistors (mosfets) in a bridge configuration. The gates of the mosfets are controlled by an input signal which is amplified in a diamond differential amplifier phase splitter and voltage gain stage and then applied to the mosfet gates. The power terminals (sources and drains) of the mosfets receive a power signal which varies with the input signal at a level sufficient to maintain headroom above the output signal but to reduce power dissipation in the mosfets. The power signal is produced by a switch connected between a floating power supply and a filter and operated at e.g. 200 KHz. The switch is operated by a pulse width modulated (pwm) signal derived from the absolute value of the input signal. Because the power signal in effect tracks the output signal, little power is dissipated in the mosfets so that the amplifier can be made very compact. Because of the bridge configuration, only one switch, one floating power supply and one pulse width modulator are used, reducing cost. Feed forward compensation in the pulse width modulator varies the pulse width of the pulses operating the switch inversely with changes in the power supply voltage, allowing the floating power supply to be unregulated.