Abstract: A variable resistor having a short-circuiting member which is displaced in response to the generation of abnormally high heat in the resistance member of the variable resistor with a piece thereof in contact to short-circuit the input and output terminals of the resistance member. This results in a bypass for large current, so that a protection circuit in an output amplifier is operated to suspend the generation of heat.

Abstract: A fader controlling variable resistor adapted to adjust the balance in sound volume of the right and left loudspeakers, or the front and rear loudspeakers. When abnormal heat is generated in a variable resistor in a fader control circuit, the sliding piece of the variable resistor is disconnected from the resistance member by the utilization of a thermo-plastic resin of a low-melting-point material is readily deformed or molten by heat, to prevent a fire attributed to the generation of heat therein. In one embodiment of the invention, the sliding piece is maintained in contact with the resistance member against its elastic force by a protrusion of thermo-plastic resin. When abnormally high heat is generated in the variable resistor, the protrusion is molten, and the sliding piece is disconnected from the resistance member or the conductor.