Abstract: There is provided a load detector for determining whether a load is connected to an AC-AC power supply. The power supply comprises a transformer having a primary winding and a secondary winding, the primary winding being coupleable to an AC voltage supply via a switch, and the secondary winding being coupleable to a load. The load detector comprises a signal generator for generating a signal; a sensor for detecting the signal, the sensor being arranged to detect the signal if a load is coupled to the secondary winding and to not detect the signal if a load is not coupled to the secondary winding; and switch control circuitry coupled to the sensor and being arranged to keep the switch closed if the sensor is detecting the signal and to keep the switch open if the sensor is not detecting the signal. There is also provided an AC-AC power supply comprising such a load detector.

Abstract: A power multiplier system for an amplifier comprises a power multiplier control stage, an amplifier stage and a first switching stage connectable to the power multiplier control stage. The amplifier stage is connectable to the power multiplier control stage. The power multiplier system has a first output terminal and a second output terminal, the amplifier stage is connectable to the second output terminal for driving a load connectable between the first and second output terminals. The first switching stage is connectable to the first output terminal to apply a switchable DC voltage level to the first output terminal. There is also disclosed a method of amplifying the power output of an amplifier system.

Abstract: An amplifier system comprises a first amplifier arranged to receive an input signal and a second amplifier arranged to receive a proportion of the input signal. A first potential divider is arranged to receive the output signal of the second amplifier and to feed a proportion of the output signal to the first amplifier. The first amplifier is arranged to subtract the proportion of the output signal of the second amplifier from the input signal to produce a difference signal for amplification by the first amplifier. There is also disclosed a method of amplifying a signal.

Abstract: An amplifier system comprises an amplifier, a comparator connectable to the amplifier to compare an incoming signal with a number of reference potentials. A switching stage is controlled by the output of the comparator and arranged to select a voltage level to be applied to one side of a load, such as a loudspeaker system. A subtractor is included to subtract from the incoming signal a percentage of the selected voltage level to be applied to the load. The amplifier receives the output signal of the subtractor, amplifies that signal and applies it to a second side of the load. There is also disclosed a method for amplifying a signal.