Abstract: A spectrum display device for audio use includes a first differential amplifier circuit and a first capacitor forming a low pass filter. A second differential amplifier circuit and a second capacitor form high pass filter; A band pass filter circuit is formed by the low pass filter and the high pass filter; A band selection circuit selectively sets a frequency band of the band pass filter circuit out of a plurality of predetermined frequency bands through selective setting of the operating currents of the first and second differential amplifier circuits.

Abstract: An ECL output circuit includes an emitter differential pair of transistors, a positive voltage source connected to the collectors of this pair of transistors, a reference voltage source, a constant current supplying circuit, and an output circuit. The emitter differential pair of transistors has their emitters connected together, the base of one of them is connected to an input terminal where an input voltage is adapted to be applied, the reference voltage source is adapted to apply a reference voltage to the base of the other of the pair of transistors, and the positive voltage source is connected to their collectors.

Abstract: The present invention includes a first amplifier, a second amplifier, a switching circuit for switching power from a power source line at a frequency exceeding an audible frequency and feeding the first or second amplifier, a control circuit for controlling a switching period of the switching circuit such that the feeding power is changed correspondingly to a level of the audio signal correspondingly to a first difference in voltage between one of the audio signal and the audio signal amplified by the amplifier and the power or a second difference in voltage between one of the audio signal and the audio signal amplified by the second amplifier and the feeding power, a smoothing circuit for smoothing a power fed by said switching circuit and a capacitor adapted to be charged by a portion of current flowing from said smoothing circuit when the switching circuit is in OFF state and generating discharge current to be added to the output of one of the first and second output stage amplifiers when the switching cir

Abstract: The present invention includes a first push-pull amplifier for amplifying an audio signal, a second push-pull amplifier for inverting and amplifying the audio signal, a switching circuit for switching power from a power source line at a frequency exceeding an audible frequency and feeding the first or second amplifier, a control circuit for controlling a switching period of the switching circuit such that the feeding power is changed correspondingly to a level of the audio signal correspondingly to a first difference in voltage between one of the audio signal and the audio signal amplified by the amplifier and the power or a second difference in voltage between one of the audio signal and the audio signal amplified by the second amplifier and the feeding power and a capacitor provided between the outputs of the first and second amplifiers, a loud speaker being driven by outputs of the first and second amplifiers.