Abstract: A stereo signal demodulating circuit of a switching type is provided with a differential amplifier to obtain difference signals between two output signals from the switching circuit. The difference signals from the differential amplifier are added to the stereo composite signal to obtain the left (L) and right (R) audio signals. The beats between the harmonics of the switching signal and the sub-channel signal are removed at the differential amplifier without the use of SCA filter.Two operational amplifiers may be used in place of the differential amplifier.

Abstract: A brushless DC motor capable of change of rotational direction is disclosed. The feed of a high-frequency voltage signal to switching elements is sequentially changed to orderly excite stator windings by the outputs from rotor angular position detectors so that the rotor is rotated in a desired direction. Another high-frequency voltage signal is applied to the switching elements at a time when opposite direction rotation is required, so that the high-frequency voltage signal applied to one of the switching elements in response to the outputs of the detectors is cancelled by the other high-frequency voltage signal. Therefore, the order of the excitation of stator windings is inverted and, thus, the rotor is rotated in the opposite direction.The other high-frequency voltage signal has the same frequency as, a greater amplitude than, and a phase difference of 90.degree.-270.degree.

Abstract: A stabilized DC power outputs supply devices for providing a plurality of DC power outputs which are selectively consumed, is provided by use of a single power control circuit. A plurality of DC power outputs are taken out from the single power control circuit through rectifier circuits and low-pass filter circuits. A voltage of each of the DC power outputs is sensed by a corresponding voltage sensing circuit and is compared with a corresponding reference voltage at a corresponding voltage comparing circuit. Detecting circuits for detecting one of the DC power outputs which is being consumed are provided to apply to a control signal generator the output of one of the comparing circuits which is corresponding to the DC power output detected by the detecting circuits. The control signal generator provides a control signal to the single power control circuit to stabilize the voltage of the DC output which is being consumed.

Abstract: A negative feedback operation of a PWM-type amplifier is stabilized by the use of a resistor. The input signal is voltage-compared with the triangular wave of a higher frequency than the input signal to form a PWM-signal, which is, in turn, power amplified and is provided to a load after demodulated by a low-pass-filter. A part of the output voltage is fed back from a common connection point of an inductor and a capacitor of an LC-filter forming the low-pass filter. A resistor is connected in series with the capacitor, and the negative feedback operation is, thereby, stabilized.

Abstract: A loudspeaker device comprises a bass reflexing duct formed on an enclosure on which the loudspeaker unit is provided, a passive radiator provided on the enclosure; an acoustic impedance body provided between at least one of the duct and passive radiator and the loudspeaker unit, so that the resonance frequencies of the duct and the passive radiator are different from each other thereby to markedly improve the low acoustic compass characteristic thereof.

Abstract: A power amplifier circuit having a differential amplifier at an input stage and a following complementary symmetry circuit which is driven by a pair of opposite phase output signals of the differential amplifier as a push-pull circuit. One of the pair output signals is directly applied to a transistor of the complementary symmetry circuit and the other is applied to the other transistor of the complementary symmetry circuit through a phase-inverting transistor which forms a current mirror circuit together with a diode or a transistor being connected in the collector circuit of the transistor of the differential amplifier corresponding to the other output signal. So that the pair of opposite phase output signals are applied to two transistors of the complemeary symmetry circuit after being converted into in-phase signals.

Abstract: A circuit device for generating a synchronous signal in synchronism with a steady wave component of an input signal and including a first phase-locked loop using the input signal as a reference signal, a second phase-locked loop using an output signal of a voltage controlled oscillator (VCO) of the first phase-locked loop as a reference signal, and a feedback circuit for feeding back and adding an output signal of a VCO of the second phase-locked loop to the input signal. The synchronous signal is stably obtained at the output of the VCO of the second phase-locked loop, even if the level of the steady wave component is relatively low. The level of the fed back signal may be controlled in response to the level of the steady wave component whereby the oscillation of the circuit device may be prevented.

Abstract: A coil mount structure for use in a loudspeaker of moving coil type is disclosed which comprises a generally cylindrical member at around one end portion of which a center peripheral portion of a diaphragm and an inner peripheral edge portion of a damper are removably fixed and at around the other end portion of which a coil is provided.

Abstract: The output voltage of an AM synchronous detector is compared with a reference potential level by a voltage comparator. A muting device connected with the output of the detector is controlled by a control circuit connected with the comparator. Through this control circuit, the detector output is immediately muted when the detector output level falls below the reference potential level, and the muting of the detector output is removed after a predetermined retardation when the detector output level exceeds the reference potential level.

Abstract: A frequency synthesizer including a phase-locked loop (PLL) is provided which does not use any variable frequency divider. The output of a reference frequency oscillator is applied to a phase comparator in the PLL through a monostable multivibrator. The oscillating frequency of a voltage controlled oscillator (VCO) in the PLL can be selected by controlling a bias DC voltage applied to a control element in the VCO. The output waves from said VCO are counted at a counter during a period of the reference frequency from the reference frequency oscillator of the PLL. The count operation is repeated at a predetermined time interval. After completion of each count operation, the number in the counter corresponding to the least digit column of the decimal number is discriminated to determine whether it is within a predetermined range or not. The range is determined correspondingly to a locking range of the PLL.