The mighty capacitor

One piece of the break in pie has to be a slice of capacitor. Capacitors are found in every piece of the stereo reproduction system: in the power supply converting AC to DC, speaker crossovers, analog EQ, the RIAA curve of a phono preamp, a rumble filter. Capacitors smooth the ripples we don't want, emphasize the waves we do want. They stop unwanted DC from passing through the system and a host of other duties too numerous to detail. Capacitors also add greatly to the sound of our products. There are good sounding types and bad ones too, and their sound quality depends on how they're used and what type they are. Most designers work hard at eliminating them from the signal path. You've heard the term Direct Coupled? This means no capacitors in the signal path. Capacitors come in many shapes, sizes and construction: electrolytics, films–including Teflon, Mylar, Polypropylene, polystyrene, polyester, polycarbonate, PTFE–film and foil, ceramic, silver mica, oil filled, glass, etc., etc. And each sounds different depending on how they are used. For example, silver mica capacitors are excellent as high frequency shunt bypasses at the input of an audio device, lousy sounding in the feedback loop of that same product. Here's another example. Electrolytics make bad sounding input coupling capacitors, compared to the same value of film and foil types. A good electrolytic, bypassed by an excellent film and foil combination, sound better on a low impedance output than does the same value film capacitor. And if all these combinations aren't enough to make your head hurt–and there are hundreds more to learn–each of these capacitors change their electrical characteristics with use. This means a fresh capacitor soldered into a circuit board sounds different to an identical one that's been in use for some time. That's break in at its clearest. What's going on? A number of things, but primarily something called forming. We'll touch more on this by way of example tomorrow. I'll try not to make the discussion too technical. In fact, maybe not technical at all. If I can manage.