Switching amplifiers

A controller for controlling a switching amplifier to modulate voltages at first and second output nodes so as to drive a load connected between said first and second output nodes with a differential drive signal based on an input signal, wherein:

• the controller is configured to control the switching amplifier to operate in at least a first mode of operation in which the first and second output nodes of the switching amplifier are selectively modulated between first and second switching voltages with respective controlled duty-cycles;
• and
• the controller is configured to control said duty-cycles so as to controllably vary a common-mode voltage applied to the first and second output nodes in operation in the first mode;
• wherein the controller comprises a first control loop for controlling the common-mode voltage and a second control loop for controlling the differential drive signal.