Abstract: A circuit for correcting an AC output signal from an electronic device into closer correspondence with an AC input signal to the combination of the circuit and device comprises first and second amplifiers arranged to each receive the input signal. The first amplifier is also arranged to receive feedback of the output signal from the electronic device for providing a signal which is a function of the difference between the input and output signals. The combination of signals from the first and second amplifiers is provided to the electronic device for producing an output signal which corresponds closely to the input signal.In a method of operating the circuit with an electronic device from which the output signal variably differs from the input signal, the amplitude of the output signal fed back into the first amplifier is adjusted to provide a null AC signal from the first amplifer at the output signal which deviates least from that desired.