Abstract: An improved ultrasonic cleaner is disclosed. Transducers are attached to a tank to vibrate liquid within the tank. A drive circuit is linked with the transducers to cause the transducers to oscillate at ultrasonic frequencies. The drive circuit includes an oscillator and a counter. The oscillator produces an ultrasonic signal. The counter divides the ultrasonic signal and feeds divided signals back into the oscillator to modulate the amplitude of the ultrasonic signal within a square-wave envelope and to step the frequency of the ultrasonic signal at discrete values about the center frequency.