Abstract: A class-D amplifier that amplifies an input audio signal includes: a push-pull circuit that has at least two switching transistors; an electric current suppressor that is disposed between the push-pull circuit and a power source that supplies electric power to the push-pull circuit; a switch that is connected in parallel with the electric current suppressor; a determiner that determines whether or not the class-D amplifier is in a state where sound is not emitted; and a controller. When the determiner determines that the class-D amplifier is in a state where sound is not emitted, the controller turns off the switch such that a path for electric current flowing from the power source to the push-pull circuit runs through the electric current suppressor. When the determiner determines that the class-D amplifier is in a state where sound is emitted, the controller turns on the switch such that the path for electric current bypasses the electric current suppressor.

Abstract: A class-D amplifier that amplifies an input audio signal includes: a push-pull circuit that has at least two switching transistors; an electric current suppressor that is disposed between the push-pull circuit and a power source that supplies electric power to the push-pull circuit; a switch that is connected in parallel with the electric current suppressor; a determiner that determines whether or not the class-D amplifier is in a state where sound is not emitted; and a controller. When the determiner determines that the class-D amplifier is in a state where sound is not emitted, the controller turns off the switch such that a path for electric current flowing from the power source to the push-pull circuit runs through the electric current suppressor. When the determiner determines that the class-D amplifier is in a state where sound is emitted, the controller turns on the switch such that the path for electric current bypasses the electric current suppressor.

Abstract: A process for producing a highly crystalline .alpha.-olefinic polymer in a high yield, which comprises contacting propylene or a mixture of propylene and another .alpha.-olefin with a mixed catalyst system produced by adding a lactone as the third component to a catalyst system consisting essentially of titanium trichloride (1) and a dialkylaluminum halide (2), by which the by-production of the undesired atactic polymer can be decreased.