Power amplifier whose bias voltage changes depending on power supply voltage

A power amplifier comprising a differential amplifier having a first input terminal receiving an input signal and a second input terminal, a bias circuit connected between first and second power supply terminals and having a bias terminal coupled to said first input terminal, a drive stage receiving the output from said differential amplifier, a single-ended push-pull output stage driven by said drive stage, an output terminal coupled to said single-ended push-pull output stage, a feedback circuit coupled between said output terminal and said second input terminal, said single-ended push-pull output stage having a first compound transistor coupled between said first power supply terminal and said output terminal and a second compound transistor coupled between said output terminal and said second power supply terminal, said first compound transistor being activated by a voltage applied between said first power supply terminal and said output terminal, said second compound transistor being activated by a second voltage applied between said output terminal and said second power supply terminal, said first voltage being larger than said second voltage, said bias circuit including a first series connection of a first constant voltage generating means and a first resistor inserted between said first power supply terminal and said bias terminal and a second series connection of a second constant voltage generating means and a second resistor inserted between a said bias terminal and said second power supply terminal, and a third resistor connected in parallel to said second constant voltage generating means.