Impedance vs. regulation

In yesterday's post, I wrote about the importance of lower impedance in the AC line voltage. I mentioned that lowering the impedance is far more important than cleaning up the AC line noise (a subject for yet another post as this goes against nearly all the conventional wisdom). I got a lot of mail asking me to explain how regulating the voltage could result in lowering the impedance. They seem like very different processes. Let's give a quick look at what it means to have low impedance. It's probably helpful to use an audio example first. Let's start with the output of a power amplifier. Years ago, in the days of output transformer-coupled tube amplifiers, output impedance mattered greatly. Looking at the back of one of those amps, you'd notice different speaker connections: 8Ω and 4Ω. These were necessary to match the relatively high impedance of the amplifier to the speaker. Put a 4Ω speaker on the 8Ω tap and you're going to lose voltage/loudness. This mismatch is because of our old friend Ohm and his law: a high impedance feeding a low impedance results in a loss of voltage. A low impedance feeding a high impedance offers little to no loss. Ergo: we always want a low impedance feeding a high impedance. Back to the AC line. Suppose a power amp draws enough current to play a big loud bass note. In that case, the inherent impedance in the hundreds of feet of wire connecting your home's AC socket to the utility pole outside your house is more than enough to result in a significant voltage drop (sometimes 3 to 4 volts or more). This modulation of the voltage is sonically unwanted in an amplifier. If, on the other hand, an AC regenerator like a Power Plant is inserted after the AC socket, its ability to tightly regulate the voltage means there will be no voltage drop—as if there were only inches of wire as opposed to hundreds of feet. Hundreds of feet of wire = high impedance. Inches of wire = low impedance. Hope that helps.