On the metallicity dependence of Wolf-Rayet winds

A power amplifier device comprising first and second output terminals connected to a loudspeaker, and a power amplifier having a non-inverting input supplied with an audio signal, an output connected to the first output terminal and an inverting input. The second output terminal is grounded through a first resistor and connected to an input of an inverting amplifier having a gain of -1. An output of the inverting amplifier is connected to the inverting input of the power amplifier through a second resistor. The output of the power amplifier is connected to its inverting input through a third resistor. The ratio of the third resistor to the second resistor is selected to be larger than 1 whereby the output impedance of the power amplifier device as seen from the first and second output terminals is made to be negative.

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