Real-time audio video applications require guaranteed request service times from a hard disc drive. The method includes the steps of forming a growth mode control layer controlling the growth mode of the carbon nanotubes, forming a catalyst layer on the growth mode control layer, and causing the carbon nanotubes to grow by heating the catalyst layer by thermal CVD so that the carbon nanotubes serve as the interconnection part. In order to produce harmonics which are as low as possible with respect to the fundamental of the voltage and the current of an electrical AC voltage system which is connected on the input side to the converter circuit, n transformers are provided, each having a primary winding and m three-phase secondary windings, where n\u22672 and m\u22673.