We're starting part 2 of our continuing story of how AC power affects the quality of our hi-fi systems, how vibrations and microphonics do the same and then part 3 will be how we deal with them all together for great benefit.
In part 1 we learned how and why power affects the sound quality - and part of that learning showed us that without perfect DC to run our amplifiers, we get a not-so-perfect output feeding our loudspeakers. This is called distortion and the term distortion simply means a deviation from what we started with - an imperfect version of the original.
Whatever was on our disc, in the form of music, needs to be amplified without distortion to make perfect music in our rooms. In other words we need to transfer a perfect copy of what was on the recorded medium and get it into the room. The closer we get to perfection the better it sounds.
We know that if we have less than perfect power, our goal of a perfect copy of the music cannot be achieved because we've added or subtracted something from that music. The same can be said for another form of distortion: microphonics.
Microphonics is a well understood distortion but most of us don't thoroughly understand it and, even if we did, don't know how to minimize it effectively.
So let's start with the basics and understand what it is. Microphonics is the tendency of something to act like a microphone picking up sound. A good example of microphonics might be a tube in a preamplifier. If you were to open up a tube preamp, turn the volume up high and flick your finger against one of the amplifying tubes, you'd hear the sound of your fingernail striking the glass envelope of the tube in your loudspeaker. That's the tube acting like a microphone. Tubes are notorious culprits as are capacitors. In fact, just about everything in your analog hi-fi electronics is microphonic to some extent.
I remember an ad for software you could load onto a PC that turned any sound card into a microphone (without a microphone) and allowed you to snoop in on some poor unsuspecting person's conversations. This worked because of the tendency of the capacitors on the sound card to act like microphones and if you amplify it enough you can actually hear what's going on in the room.
Many modern microphones of the highest quality are actually capacitors optimized for full range sound recording.
Your DAC, preamp, power amp, CD player etc. are all microphones that pickup sound and add it to the music.