Abstract: An equalizer circuit is provided which has a high D.C. stability without degrading the equalization characteristic. The equalizer circuit comprises an equalizer amplifier, an equalizer element, a direct current component detecting circuit, and a negative feedback circuit. The equalizer amplifier amplifies an input signal of the equalizer circuit in accordance with RIAA equalization characteristic. The output of the equalizer amplifier is applied to the equalizer element which has an impedance corresponding to an inversed RIAA equalization characteristic. The output from the equalizer element, which is not subject to the RIAA equalization characteristic due to the provision of the equalizer element, is supplied to the direct current component detecting circuit in order to derive a direct current component from the output. The derived direct current component is negative fed-back to the equalizer amplifier as a negative feedback signal thereof.

Abstract: An amplifier arranged so that, when a plurality of power supply voltages supplied to an amplifying device are switched over in accordance with a signal voltage level of the amplifying device, the reference voltage provided for comparison with the abovesaid signal level will follow the fluctuations of the voltage of the lower voltage power supply among said plurality of power supplies, whereby avoiding the starting of operation of the amplifying device in its saturating region to thereby prevent increase in distortion of an output signal.