I've just been having a discussion elsewhere about the performance of aluminium electrolytic caps for audio coupling in a zero bias situation. This is a method very widely used nowadays.
I've observed, indeed I first heard of it decades back, that provided the signal
*across* the capacitor doesn't exceed about 100mV ac there is no measureable non-linearity. I've confirmed this using Audio Preciosn test gear which measures down to 0.0008% THD (-102dB). Hence if the value of the cap is such that 100mV is never exceeded, there will be no distortion contribution from the cap. I've also confirmed that if the 100mV is exceeded, you do indeed get distortion.The mechanism seems to be electrolytic rectification AIUI. I presume that the absence of any effect below ~ 100mV is due to the 'forward' voltage of this rectifier, and current only flows when it's exceeded.
Any more thought on this ?
I did find this page about electrolytic rectification btw.
The oscillograms are rather interesting.
Graham