The sound of coupling capacitor

What is a coupling capacitor?

So if the at-rest DC voltage at the output of one internal stage is 5 V, but only 2 V at the input to the next stage, a coupling capacitor is placed in the signal path to allow audio to pass without upsetting the DC voltage difference. A capacitor is constructed from two metal plates in close proximity but not quite touching.

Do coupling capacitors affect sound quality?

This is equally true for the output coupling capacitors of the preamp. Certainly the designer of the circuitry must do the job properly, but given that this is accomplished, and given that the amplifier has adequate power and power-supply stability to do the job at hand, the purity of the sound is very dependent on the coupling capacitors used.

Do amplifiers use capacitor coupling?

This doesn't mean that capacitor coupling is not used though, and there are a surprisingly large number of amplifiers that still use an output capacitor. These are primarily low-power designs, and they are used in many consumer products because they are cheaper to build than a dual supply. The current paths are also exactly what you'd expect.

Do coupling capacitors cause distortion?

Coupling capacitors in series between stages of an audio circuit generally have a large enough value to roll off starting below 20 Hz. Since little audio voltage is lost across a coupling capacitor at the higher audible frequencies, in theory their distortion should not be a factor. This is exactly what I set out to prove or disprove with my tests.

Why are coupling capacitors used between stages?

The internal input and output points of many circuits are not centered at 0 VDC, so coupling capacitors are used between stages. This is especially needed with tube devices, but also with many solid-state circuits that use discrete transistors instead of op-amps.

What does a capacitor do?

For a more detailed look at capacitors in general, have a look at Capacitor Characteristics. That article covers many of the points made here, but in somewhat greater detail. The purpose of a coupling cap is to pass the wanted audio (AC) signal, while blocking any DC from preceding stages or source components.