A current detection unit of an inverter outputs currents to a load, such as a motor includes a device for measuring a DC current flowing in the inverter. When the audio signal to be received is changed, a process to be executed is changed depending on the transmitting scheme of the audio signal. The compressor is connected to a cooling medium circuit which contains a condenser, an evaporator and an expansion means arranged therebetween. The yo-yo is also adapted for use with a spring-powered winder. The membrane is used for separating oxygen from air or from a gas mixture containing same and in particular for producing ultra-pure oxygen under high pressure in a closed chamber. The ballast in one embodiment may be a washer replacing embedded projectiles.