Abstract: Apparatus and method for producing ultrasonic sound waves used to disperse rodents including negative feedback damping of a tuned band-pass filter output circuit. An electrical signal is frequency modulated, amplitude modulated asynchronously with the frequency modulation, pulsed on and off and applied to a speaker to produce ultrasonic sound waves corresponding thereto. The output signal is passed through a tuned band-pass filter circuit which includes negative feedback damping to reduce the power consumption of the amplification of the output signal and in part to produce the band-pass characteristics of the band-pass filter output circuit.