Abstract: A recording/reproducing circuit according to the present invention comprises a recording amplifier for outputting a recording signal, a differential amplifier including a pair of transistors, a base of one of the transistors being a (+) side input, a base of the other transistor being a (-) side input, emitters of the transistors being connected commonly to a current source, the (+) side input being supplied with the recording signal, an output signal being fedback to the (-) side input, the output signal being sent to a recording head and means for cutting a current of the current source to thereby stop an outputting of the recording signal from the differential amplifier circuit.

Abstract: An audio amplifier circuit according to the present invention features an arrangement of a power line with a smoothing capacitor inserted as a power filter and a power line without such a smoothing capacitor. The audio amplifier circuit in which an input stage amplifier of a main amplifier is supplied with power via the former power line has a muting circuit for rapidly charging a negative feedback capacitor for generating negative feedback voltage to be fed back from the following stage of the main amplifier to the input stage amplifier up to a voltage level at which a pop sound is inhibited when the power is supplied and for rapidly discharging the negative feedback capacitor up to a reference operating voltage level when the voltage of the former power line with the smoothing capacitor exceeds a predetermined level, the voltage of the former power line being monitored after the power is supplied from a power supply.