Distributed Capacitance

Author: N.H. Crowhurst

Stray capacitance that loses high frequencies is distributed everywhere in the audio circuit.

Loss of high-frequency response occurs because of capacitance we cannot avoid, although it is not in the form of an actual capacitor. A capacitor is a component in which natural capacitance is exaggerated by putting large areas of foil in close proximity to one another. This produces capacitance values that are measured in microfarads. However, the presence of electrical circuits (conductors, components, chassis) in the same space produces a capacitance between different points, although it is measured only in micromicrofarads.

It is this capacitance that causes loss of high frequencies. At the frequency where the reactance of the total capacitance between the audio circuit and ground is equal to the effective circuit resistance, there will be a phase shift of 45° and 3-db loss in audio level.

Manufactured capacitor (left) vs. stray capacitance (right)