A power amplifier for amplifying an electric input signal in an operational frequency range and providing an output signal, comprising switching means (22), filter means (14, 15) for generating a power output signal by low pass filtering a block wave signal, input means for receiving the electric signal and feeding it to a first input of the switching means, the power amplifier further comprising a feedback circuit (24) connecting the output signal to the first input of the switching means. The power amplifier comprises a servo amplifier (32) connected to receive an error signal appearing at the first input of the switching means and to feed a correction output signal to a second input of the switching means (22) for neutralizing an impact of the error signal on the output signal. The invention relates to a method of amplifying an electric input signal in an operational frequency range. The method includes the steps of obtaining an error signal present at said first input of the switching means, amplifying the error signal in the operational frequency range, inverting the error signal and feeding the amplified and inverted error signal to a second input of the switching means.