A transistor amplifier consisting of a modulated radio frequency generator and a detector circuit wherein the operating portion of the input-output curve of the radio frequency generator is a complement of the operating portion of the input-output curve of the detector circuit. The curvature of the radio frequency generator is controlled by variation in the current of a radio frequency voltage through a diode, changing the loading on a tuned circuit so that the amplifier may be adjusted for low, zero or negative harmonic distortion. The amplifier may be adjusted to compensate for distortion in equipment connected to its input terminals or distortion in equipment connected to its output terminals.

A switching amplifier comprises an input terminal connected to a d.c. power supply and an output terminal connected to a load. At least one power transistor is placed in series with the input and output terminals. A PWM circuit outputs a pulse width modulated signal. An isolating driver circuit between the PWM circuit and the control terminal of the power transistor comprises a low voltage power supply; a transformer having primary and secondary windings; an oscillator for outputting a high frequency signal; means for gating the high frequency signal from the oscillator to the primary winding of the transformer in response to the pulse width modulated signal from the PWM circuit; a MOSFET; means for rectifying the voltage in the secondary winding of the transformer and for applying the rectified voltage to the gate of the MOSFET; and switching means for rapidly discharging the gate of the MOSFET when the high frequency signal is no longer gated to the transformer.

There is provided an audio power amplifier having an output DC isolated from ground between two capacitors which are connected in series across a bias potential. The bias potential may be generated from common AC line currents by a simple bridge rectifier without the need for a bulky power supply transformer. The amplifier is DC isolated from the input signal, and hence from ground, by a balun or other small-signal transformer. Feedback is provided to compensate for ripple appearing on the bias potential.

In a high-fidelity, high-power audio amplifier, the power supply makes direct connection is made to the AC line, followed by appropriate rectification and filtering, but without the need for a power transformer. The invention is not limited in terms of the class of amplifier, and may be applied at least to class A and class AB configurations. The input is AC-coupled without the use of a ground potential, preferably using capacitive coupling. To provide voltage levels appropriate for referencing and other purposes, a pseudo-ground is established, preferably through the use of a resistive ladder across the rectified line. The use of this divider network not only provides DC voltages to operate integrated components such as operational amplifiers, but also serves to provide reference signals for differential amplifiers in the output stages.