Abstract: A power amplifier stage for an audio amplifier is constituted by a complementary pair of one N channel and one P channel unsaturated function FETs forming a single ended pushpull circuit. The stage is energized by a first d.c. power source. The gate potentials of the FETs are controlled by a series of control type constant voltage source comprising a pair of complementary series connected control transistors energized by a second d.c. power source which varies at the same rate as the first d.c. power source. A comparison circuit including a second pair of complementary transistors is connected to a d.c. reference voltage which varies to a smaller level than the first and second d.c. power sources in order to provide a constant quiescent current flowing in the drain circuits of the FETs even if the first and second d.c. voltage levels fluctuate.

Abstract: A four channel decoding apparatus comprises means to form signals LT+RT, LT-RT, +jLT+RT; LT+RT, LT-RT; and LT+jRT, LT-jRT, for example, from composite signals LT and RT depending upon the type of the matrix four channel systems and means for additively and subtractively combining these sum and difference signals to produce four reproduced signals.

Abstract: Improvements in a stereo signal demodulator of a receiver in a four-channel stereo system, in which system upon transmitting four sound source signals (LF, LB, RF and RB) from one station, the transmission is carried out for a synthesized signal composed of a signal in a main channel of (LF + LB) + (RF + RB), a pilot signal, a signal in a first sub-channel consisting of a double side-band signal obtained by modulating an m-multiple frequency-multiplied signal of the pilot signal with a signal of (LF + LB) - (RF + RB), a signal in a second sub-channel consisting of a double side-band signal obtained by modulating the same, m-multiple frequency-multiplied but phase-shifted signal with a signal of (LF - LB) + (RF - RB), and a signal in a third sub-channel consisting of a single side-band signal (SSB or VSB) obtained by modulating an n-multiple (m < n) frequency-multiplied signal of the pilot signal with a signal of (LF - LB) - (RF - RB).

Abstract: A sound reproducing device comprising a first (low frequency) speaker and a second (high frequency) speaker, the high frequency speaker mounted within its own housing which allows rear-cone radiation out the housing sides, in addition to front-cone radiation out the front, thereby improving radiation efficiency and transient response.

Abstract: A composite signal for a four-channel stereo broadcast includes a main channel component, first and second sub-channel components and at least one pilot signal. The composite signal is fed to a stereo signal demodulator through an FM tuner. The stereo signal demodulator derives the pilot signal out of the composite signal to produce first and second sampling pulse series, each sampling pulse having a different repetition frequency. The first sampling pulse series is fed to a delay circuit that is provided with electronic delay lines such as dynamic shift registers. The delay circuit is switched by the first sampling pulse series for sampling the composite signal, to shift sampled values. Sampled values delayed in the delay circuit are fed to a logical circuit to derive the main and first sub-channel components. The second sampling pulse series is supplied to a switching circuit for demodulating the second sub-channel component.

Abstract: A speed control device for a transistor motor having a stator provided with a plurality of field windings and a rotor consisting of a permanent magnet comprises position detecting means for detecting the position of the rotor, a plurality of driving transistors whose emitter-collector circuits are respectively connected in series to the field windings and whose bases are respectively supplied with the output from the position detecting means, a base current control transistor for the driving transistors whose emitter-collector circuit is connected through diodes to the respective bases of the driving transistors, and a servo circuit for maintaining the base current control transistor to be inoperative during the starting period of the transistor motor and, as the transistor motor approaches a specified rotation speed, controlling the base current of the driving transistors in accordance with a speed control signal.

Abstract: A matrix four-channel decoding system wherein the mixing coefficients or mixing ratios of left and right composite signals of medium frequency range are continuously changed in accordance with the level conditions of directional audio input signals contained in the composite signals and the mixing coefficients or mixing ratios of the left and right composite signals of low and high frequency ranges are substantially fixed, thereby attaining the more natural four-channel reproduction.

Abstract: A brake mechanism in a magnetic tape recording and reproducing machine in which a magnetic tape is transported from one reel to the other reel comprising brake drums corresponding to two reels, brake shoes, means for securing the brake shoes and means for pressing the brake shoes to respective brake drums. Two micro-switches are provided for detecting the displacement of the respective means for securing the brake shoes in the direction of the rotation of the respective brake drums caused by the friction between the brake shoes and the brake drums in the operation of the brake mechanism.The two micro-switches are used for controlling a circuit giving D.C. current to stator windings of two electric motors for driving respective reels so that the rotors of both motors may be subjected to electromagnetical braking. The two micro-switches are also used for prohibiting the machine from starting until the tape transportation is perfectly stopped after operation of the brake mechanism.

Abstract: To the output side of a matrix four-channel decoder for producing four outputs while controlling the mixing coefficients of left and right composite signals in accordance with the level or instantaneous amplitude relationship between directional audio input signals contained in the composite signals are connected first and second low frequency mixers respectively receiving front pair outputs and back pair outputs. The mixers respectively mix two input signals supplied thereto with each other when they fall within a low frequency range, thereby developing mixed outputs thereof at its two output terminals, and, when they fall within the high frequency range, develop the two input signals at its two output terminals respectively. Each of mixed outputs of the first mixer is a sum of the composite signals while each of the mixed outputs of the second mixer is a difference signal thereof.

Abstract: The invention discloses a system for synthesizing first and second recording or transmission signals adaptable for both of a discrete four-channel stereo sound reproducing system and a matrix four-channel stereo sound reproducing system. The first recording or transmission signal includes a first audio main signal and a first carrier signal frequency modulated by a first audio sub-signal, whereas the second recording or transmission signal includes a second audio main signal and a second carrier signal frequency modulated by a second audio sub-signal. Each of the first and second audio main signals is formed by combining four sound signals with a predetermined amplitude ratio and a predetermined phase relationship, whereas each of the first and second sub-signals is formed by combining three of the four sound signals with a predetermined amplitude ratio and a predetermined phase relationship.