Abstract: In a power amplifier having a power circuit of a switching control system, a protective device for the power amplifier has connected to the amplifier a means for detecting an abnormal signal produced at the amplifier, and a control means connected between the detecting means and the power circuit to the amplifier so as to cut off a switching control signal to the power circuit when an abnormal signal is generated at the amplifier, thereby stopping the power circuit from operating to cut off power to the power amplifier. The detecting means is formed of a detecting circuit connected to the output end of the amplifier so as to detect the DC output voltage or excessive current from the amplifier, and a driving circuit connected to the detecting circuit so as to be operated by the output signal from the detecting circuit.

Abstract: A power supply controlled stereophonic amplifier system of a simplified circuit configuration which includes an analog logic circuit that generates a larger one of the input signals for left and right channels thereby to control the output voltage of the DC-DC converter as a power supply by means of a pulse train of pulse widths that change according to the output of the logic circuit. The output of the analog logic circuit is compressed by a signal compression means which functions to compensate for the non linear response of the DC-DC converter.

Abstract: An audio frequency power amplifier circuit comprising a voltage detector for detecting the voltage between the gates of output MOS FETs in Class B push-pull connection, and a bias generator for applying a quiescent bias voltage to the MOS FETs. The bias voltages applied to the MOS FETs are changed in proportion to the output current in such a manner that the output MOS FET to be cut off is impressed with a substantially equal bias voltage in the absence of signal. In this way, the cut off of the push-pull transistor of Class B operation is prevented, thus preventing a switching distortion.

Abstract: An audio frequency power amplifier wherein an input signal is applied to respective input electrodes of a pair of transistors of the same conductivity type to produce an output signal at an output electrode of one of the pair of transistors. A common electrode of the one transistor is connected with an output electrode of the other transistor and a power from a first D.C. power supply is supplied to the junction thereof through a diode while a power is supplied to a common electrode of the other transistor from a second D.C. power supply having a higher voltage than that of the first D.C. power supply. The other transistor and the diode are alternately rendered conductive and non-conductive in response to the signal level of the input signal, a capacitor is connected to the input electrode of the other transistor, which capacitor is charged during the turn-off of the other transistor whereby the charge is supplied to the other transistor upon turning on of the other transistor to shorten the rise time.

Abstract: An audio- or low-frequency power amplifier comprises a pair of output transistors which are opposite in a conduction type to each other and connected in a complementary push-pull circuit configuration in which an impedance element is connected between the bases of the paired output transistors whose bases are adapted to be applied with an input signal while the output signal of the amplifier is derived from the coupled emitters of the output transistors. The amplifier further includes a current stabilizer transistor having a base-emitter junction across which a fixed bias voltage is applied and a collector, the current from which is supplied to the impedance element thereby to provide a bias voltage for the paired output transistors. A first resistor is connected between the emitter of the current stabilizer transistor and one electrode or pole of a first d.c. power source while a second resistor is connected between the emitter of the current stabilizer transistor and the other pole of the d.c.