Patent ID: 8306239
Filing Date: 2012-11-06
Classification: H03F,H04R

Abstract:
1. A public-address system comprising: an audio signal source providing an audio signal between two terminals, one of said two terminals being connected to a ground potential; isolation input means having an input side to which the two terminals of said audio signal source are connected, said audio signal being developed between two terminals on an output side of said isolation input means while being isolated from said input side; power amplifying means to which said audio signal is inputted from said two terminals on said output side of said isolation input means, said power amplifying means amplifying said audio signal and outputting the amplified audio signal at a high voltage from two output terminals thereof without using an isolation transformer; a plurality of loudspeakers connected in parallel with each other between transmission lines provided respectively for said two output terminals of said power amplifying means; and DC power supply means having two ungrounded power supply terminals, generating operating power from a commercial AC power supply, and supplying said operating power to said power amplifying means through said two power supply terminals; one of said terminals on said output side of said isolation input means, one of said output terminals of said power amplifying means and one of said power supply terminals of said DC power supply means being connected together to provide a common point of potential, different from said ground potential, for said output side of said isolation input means, said power amplifying means and said DC power supply means, wherein said output side of said isolation input means, said power amplifying means and said DC power supply means operate with reference to the potential at said common potential point, which serves as a reference potential therefor.