An amplifier including a difference amplifier, said difference amplifier including a first output and a second output which are adapted for providing a PWM signal output to a load by signal difference between said first and said second outputs, said difference amplifier being adapted for operating in at least first and second alternative operating modes which are respectively characterised by first and second operating voltages, wherein during transition from one operating mode to another, the pulse area of the pulses of said first and second outputs of said difference amplifier are changed according to a pre-determined manner so that the pulse area of pulses of said first and second outputs at the end of said transitional mode is equivalent to the pulse area of the pulses of said first and second outputs immediately after the change of operating modes.