A monolithic integrated circuit amplifier has a gain stage (202) and a buffer stage (210). The buffer stage includes an output stage and two separate voltage supplies (+Vlo, +Vhi), the second of which has a greater magnitude than the first. Switching circuitry is included that is connected to the output stage via a regulator bus. When an output demand voltage is less than a switch-over threshold, current to the output stage is provided substantially from the first voltage supply (+Vlo); when the output demand voltage is greater than the awitch-over threshold, current to the output stage is provided substantially from the second voltage supply (+Vhi). Collector voltage at the output stage is dynamically controlled to be greater than the emitter voltage by a difference voltage that increases proportionally as output voltage increases above the switch-over threshold. This difference voltage is commonly reffered to as 'headroom'. The dynamic headroom control circuitry preferably includes circuitry for predicably setting and controlling the headroom voltage at switch-over and smoothly increasing the headroom voltage up to maximum output voltage.