Abstract: A noise prevention circuit of a digital audio circuit having an input side and an output side includes a signal level retention circuit having first and second inputs and first and second outputs, for retaining a level of a transmitted signal; and a switch circuit operably coupled to the signal level retention circuit for respectively connecting the first and second inputs of the retention circuit to an active line and a ground line of the input side of the digital audio circuit. The retention circuit receives and retains input signal from the active line and the ground line of the input side of the digital audio circuit, and for alternatively connecting an active line and a ground line of the output side of the digital audio circuit. The retention circuit outputs the retained signal in the signal level retention circuit from the first and second outputs of the signal level retention circuit to the active line and the ground line of the output side of the digital audio circuit.

Abstract: An apparatus for improving the salient properties of the output stages of electronic power amplifiers v.s. varying load conditions. A novel circuit, based on current feedback sensing the instantaneous drive current of the output devices, is used to linearize the output characteristics of the output devices. The important features, compared with the presently known and employed drive circuits, relate to a more linear transfer characteristic, much larger output current capability, and more output amplifier design.

Abstract: Apparatus for electronically protecting output transistors of electronic amplifiers against thermal overload, overcurrent, overvoltage, and second breakdown mechanism. An analog multiplier circuit, together with a novel circuitry for deriving the instantaneous voltages across, and the currents through, each of the output transistors, is used to obtain the instantaneous power dissipation in the transistors. A thermal sensor, the electrical signal of which is used as an additional variable in the multiplication, yields the thermal derating necessary for the transistors, and an integrating time constant used to weigh the output signal of the multiplier, takes into account the time derating of the transistors.

Abstract: A tape transport mechanism for dual capstan type tape recorders, which is designed so that a drive motor can be located at any desired position and rotational irregularities such as wow can most effectively be prevented. This mechanism includes a first flywheel provided with a first capstan for transporting a magnetic tape, and a second flywheel provided with a second capstan for imparting a back tension to the magnetic tape being transported. The first flywheel comprises a smaller-diameter portion on which said first capstan is provided, and a larger-diameter portion which is integrally provided on the bottom of the smaller-diameter portion. The larger-diameter portion of the first flywheel is coupled to the drive motor through a first belt, and the smaller-diameter portion thereof is connected to the second flywheel through a second belt.

Abstract: An FM tuner comprising means for producing an intermediate frequency signal, a frequency discriminator circuit having "S" characteristics, a differential amplifier circuit, and detector means. The bias of said differential amplifier circuit is controlled in accordance with the direct current component of the output of said frequency discriminator circuit, and part of said intermediate frequency signal is passed to said detector means through said differential amplifier circuit, whereby that frequency position of said intermediate frequency signal which corresponds to the center of said direct current component is detected. Thus, it is possible to determine whether or not the FM tuner is in an optimum tuned state.

Abstract: In a method of measuring electrical analog quantities, a first analog signal representing a first electrical analog quantity which is to be a reference is subtracted from a second analog signal representing a second electrical analog quantity which is to be compared with the first analog quantity, so that a difference signal is produced. Then, the difference signal thus produced is integrated for a predetermined time to obtain a third analog signal. Simultaneously therewith, the first analog signal is also integrated for the predetermined time to obtain a fourth and a fifth analog signal representing the positive and the negative value of the aforementioned integration. And the third analog signal is integrated between it and the fifth or the fourth analog signal in accordance with the positive or the negative sign of the third analog signal to obtain a sixth analog signal.

Abstract: A method of detecting tape transport condition, wherein a signal is derived from detector means provided in association with at least one of a pair of spindle reels of a tape recorder to detect the rate of revolution of said spindle, said signal having a frequency proportional to the rate of revolution of said spindle. The signal derived from the detector means is applied to a phase-locked loop, and it is also applied to a synchronism detecting circuit, together with a signal derived from a voltage-controlled oscillator contained in said phase-locked loop. Thus, detection is made with respect to whether or not these two signals agree in frequency with each other.

Abstract: An operating mechanism of a tape recorder, means is provided for preventing the erase head from engaging the tape to erase the tape when cue or review is effected during recording or play-back operation.

Abstract: An operating mechanism of a tape recorder, wherein when pause, cue or review is effected during recording or playback, a pinch roller and head are spaced apart from the tape. Futhermore, by the cue or review being effected, the playback position will not be released, but upon retraction of a subchassis carrying the pinch roller and head, the pressure contact relationship between the pinch roller and the capstan with the tape held therebetween will be released so that upon cessation of the cue or review, playback may be started immediately.

Abstract: A method and apparatus for detecting whether the phase difference between a first and a second signal is constant or not. A Q output and Q output are derived from a set-reset flip-flop circuit by imparting thereto a first and a second trigger pulse which are respectively obtained on the basis of said first and second signals. Subsequently, on the basis of said Q and Q outputs, there are produced two pulse signals the fall portions of which correspond to those of said Q and Q outputs respectively but the rise portions of which are caused to occur while being delayed by a period of time corresponding to the duration of said trigger pulses. Thereafter, there are produced logical products of said first and second pulse signals with respect to said first and second trigger pulses. Thus, it is detected whether the phase difference between said first and second signals is constant or not, according to whether the outputs of said logical products are present or not.

Abstract: In a cassette tape recorder including cassette receiving means pivotable between an inclined position where a cassette can be inserted therein or removed therefrom and a horizontal position where the cassette is held so that a magnetic tape contained therein can be transported, a cassette eject mechanism comprising cassette force-out means mounted on the cassette receiving means and pivotable between a first position which it is made to assume when the cassette receiving means is at the inclined position and a second position which it is made to assume when the cassette receiving is at the parallel position, and lock means mounted on the cassette receiving means for acting to lock the cassette force-out means in the second position upon the cassette being fully inserted in the cassette receiving means and to unlock the cassette force-out means when the cassette receiving means is pivoted from the inclined position to the parallel position.

Abstract: An FM tuner comprising means for producing an intermediate frequency signal, a frequency discriminator circuit having "S" characteristics, a differential amplifier circuit, and detector means. The bias of said differential amplifier circuit is controlled in accordance with the direct current component of the output of said frequency discriminator circuit, and part of said intermediate frequency signal is passed to said detector means through said differential amplifier circuit, whereby that frequency position of said intermediate frequency signal which corresponds to the center of said direct current component is detected. Thus, it is possible to determine whether or not the FM tuner is in an optimum tuned state.

Abstract: A first signal of a relatively high frequency and second signal of a relatively low frequency are alternately generated, the amplitudes of these signals varying with time. Then the first and second signals are recorded, together with a predetermined bias signal, on a magnetic recording medium by a tape recorder, and thereafter the thus recorded first and second signals are reproduced. Subsequently, detection is made of a point of time when the third harmonic component of the reproduced second signal comes to have a predetermined level ratio with respect to the reproduced second signal. The level of the reproduced second signal at the point of time to be detected as mentioned above is held, and at the same time the peak level of the reproduced first signal is also held. Thus, the bias for the tape recorder is set up at a required value on the basis of the difference or ratio between the held first and second signals.

Abstract: A method of imparting a predetermined tension to a tape transported at a predetermined velocity from one to the other of the reels mounted on a pair of reel spindles at least one of which is rotated by a motor to have a rotational torque imparted thereto, wherein detection is made of the number of revolutions of the reel spindle rotated by the motor, a signal resulting from said detection is frequency-voltage converted, then the thus converted signal is converted into a logarithmic signal, subsequently the logarithmic signal is subtracted from a reference voltage, and a signal resulting from the subtraction is supplied to the motor to thereby impart a predetermined tension to the tape.

Abstract: An amplifier circuit comprising a differential circuit including means for preventing base bias voltages applied to driver transistors connected with the transistors constituting the differential amplifier from becoming unbalanced. Means is also provided which is adapted to prevent so-called shock noise from appearing at the output of the amplifier circuit. Such means may be constructed by using a delay circuit.