The invention relates to amplifiers of audio power which operate with loudspeaker systems. The main technical result is significant extension of the reproducible frequency range without reduction of the loudspeaker system fundamental resonance frequency. This result can be obtained by means of adding only one low power resistor and one low capacitance capacitor to a typical power amplifier. In the described embodiment this is achieved by means of a rise of the amplifier FR at low frequencies using positive feedback and the quasi-resonance effect.