RF Filtering for Audio Amplifier Circuits

An important aspect of the audio amplifier circuit is the output RF filter, required to suppress RF interference produced by fast output transitions of the amplifier.[1] Early techniques for filtering the amplifier output in car stereos used traditional through-hole type feedthru capacitors. Over time, circuit designers have changed from through-hole type to surface mount chip feedthru capacitors or chip ferrite beads to lower costs. These new components add DC resistance to the audio circuit, which can increase power consumption and shorten battery life in handheld devices.
This article will show how to use a single X2Y® bypass capacitor to improve audio amplifier output performance by removing the DC resistance. The solutionalso lowers system cost through component reduction.

Car Audio
In the past, many in the automotive industry used multilayer ceramic through-hole feedthru capacitors to filter the audio amplifier output in car radios. RF filtering prevents electro-magnetic interference (EMI) from corrupting other electrical components in the car by using speaker wire or main power leads, or as a launch point for radiated noise. The through-hole feedthru capacitors provided insertion loss with no effect on the power output of the audio amplifier because the power and return wires to the speaker were fed through a hole in the center of each feedthru capacitor. The capacitor was mounted to a grounded plate so undesirable EMI could be shunted to the circuit ground reference