Abstract: A multi-drop type bus line system having a plurality of terminals respectively connected to a common bus line, in which each terminal has a connector interconnecting with the other terminals and the connectors at the respective terminals are interconnected by means of a connection cable. Each connector is provided with a switch which is actuated each time the connection cable is coupled to the connector of the terminal, whereby when the connection cable is coupled to the connector, the switch releases an impedance matching resistor connected between predetermined terminal pins of the connector. Impedance matching is improved and standing waves are reduced.

Abstract: A volume control apparatus wherein a master volume control resistor is controlled by a motor and a control circuit is provided for the motor which includes a presettable-variable resistor and a slave-variable resistor which is driven by the output shaft of the motor. A first comparator is connected to the presettable-variable resistor and to the slave-variable resistor which are in turn connected across suitable supply voltages and depending upon the relative voltages across these resistors a motor control discriminator circuit operates the motor in either the clockwise or counterclockwise direction to vary the master volume control and the slave-variable resistor until the slave-variable resistor is substantially equal to the presettable-variable resistor. When the resistance of the slave-variable resistor approaches the presettable-variable resistor the output of the master volume control is connected to an output speaker by a relay circuit.