Some Thoughts about the Material Used for Inductor Coils in Audio Amplifiers

Most of today’s audio amplifiers use a Class-D architecture. This architecture benefits from offering high power efficiency compared to traditional audio amplifiers. However, at their output, these amplifiers require a low-pass filter which is designed to remove the unwanted switching components which are generated by the switching stage. This low-pass filter is typically formed by a coil and a capacitor. Some more advanced low-pass filters operate with two coils and two capacitors.

However, the coil material has an impact on amplifier performance. In particular, the material will impact the distortion as well as the losses of the amplifier. Most notably, one parameter affects performance. It is called permeability. This parameter describes how many windings are required in order to achieve a certain inductance given a certain type of coil. The larger this parameter, the lower the number of windings per inductance.

Having a low number of windings has the advantage …