Adaptive power line noise filter and switch for audio reproduction

Abstract

A filter circuit for reducing power line noise to audio reproduction equipment. Audio reproduction equipment requires a power source without excessive line noise; however, power sources, particularly in the automotive environment, often generate a substantial amount of noise which can degrade audio reproduction quality. The present invention utilizes a filter circuit which regulates and smooths the power in line between the power source and the audio equipment. The regulation and degree of filtering is further controlled by feedback from the power output and/or from the audio output to provide a sufficient quantity of filtering at various audio levels without affecting the power transmission to the audio equipment through excessive power loss. The power output after filtering is sampled and compared to a reference voltage to create an error signal. The degree of filtering is then adjusted in response to the value of the error signal to provide appropriate filtering without excessive power loss. The audio feedback is utilized to regulate the amount of filtering to decrease the filtering and decrease the voltage loss during high audio output, and to increase filtering during low audio output to provide the necessary line noise conditioning for various audio conditions.