Abstract: A muting apparatus can mute sounds when a voltage drops even in a car audio system in which a digital audio signal is transmitted between audio components units. In the apparatus the drop of the voltage supplied to each of the audio component units is detected in each of the audio component units and, when the drop of the voltage is detected in any one of the audio component units, an analog audio signal is muted immediately before it is converted into an acoustic energy.

Abstract: A heat sink/circuit board assembly allows repairing or inspection of circuit or parts without impairing heat-radiating effect. A sub-heat sink is protruded from a lateral end of the circuit board in a direction parallel to the main surface of the circuit board and is connected to the main heat sink at its protruding portion. The diameter of the opening of the recessed portion of the main heat sink facing the circuit board is made larger than outer diameter of the circuit board. When circuit elements on the main surface of the circuit board facing the recessed portion of the main heat sink are to be repaired or inspected, the main heat sink is connected to the sub-heat sink on a main surface which is on the opposite side to the surface carrying the circuit elements, while the same heat-radiating effect as in the normal condition can be obtained.

Abstract: The present invention relates to a ground isolation circuit for use in connecting electronic circuits at the pre-stage and the post-stage having signal lines assigned for a plurality of channels, wherein the interconnection of the two electronic circuits is performed by employing a shielded signal cable for each channel, discrete ground terminals are provided at either of the electronic circuits, one for each channel, and thereby each shielding braid of the shielded signal cable is connected independently to the discrete ground terminal with every channel. Accordingly, no loop circuit is formed through the shielding braids, thus resulting in no induced noise even if there is an interlinkage of external radiation noise with the shielding braids.

Abstract: A cooling unit for cooling an acoustic device installed on the vehicle by using a cooling fan comprises a cooling fan drive circuit which outputs a DC voltage proportional to the input or output signal level of the acoustic device to control the speed of rotation of the cooling fan motor, whereby the noise of the cooling fan is suppressed in a sense of hearing when no signal is provided by the acoustic device.

Abstract: A variable characteristics amplifier circuit such as may be used in an inter-music interval detecting circuit for a tape deck, record player, or the like. First and second transistors are connected in an emitter follower configuration with an input signal being applied to the base of the first transistor. One of the emitter or collector of the second transistor is connected through a series circuit of a capacitor and resistor to an inverting input terminal of an operational amplifier, and a feedback circuit is provided between this input terminal and the output of the operational amplifier. A capacitor is coupled between the selected one of the emitter and collector of the second transistor and its base.

Abstract: A balance control circuit for controlling the difference in volume between right and left audio stereo signals. DC output voltages of an amplifier provided in a preceding stage to the balance volume control circuit are utilized as bias voltages for amplifiers provided in the rear stage of the balance control circuit, and the sliding contacts of variable resistors are grounded through a single capacitor, with the result that the manufacturing cost of the circuit is reduced.

Abstract: A separately-excited DC-DC converter having a feed-back loop for providing stable operation notwithstanding changes of load. The feed-back loop may include a temperature-responsive element so as to provide stable operation even under changes of the ambient temperature.