Wanna be a disc jockey?

Good Monday morning to you! Not sure why I started with that, but hey, Monday's can be tough. I promised yesterday I'd write a little bit about why the design of switching power supplies is so tough. We'll then cover why they are not used so much in high-end audio. Ever wonder how a radio station works? Whether AM or FM, radio stations (or for that matter cell phones as well) use a very powerful amplifier at their heart. That amplifier's output is connected to a piece of wire called an antenna. In the case of a commercial radio station, the antenna is mounted high atop a tall tower. Coming into this powerful amplifier, called a transmitter, is audio, no different than what comes out of your stereo system's preamplifier. What is different is what then happens to that audio signal before it reaches the output stage of the amplifier. The audio is passed through a device called a modulator and, depending on whether it is AM or FM, converted to a new form in preparation for being transmitted. I won't go into what that form is, although it's an interesting subject if you're ever interested. No, what's important is what happens next. When you tune your radio dial to a station, you're actually matching a frequency; the frequency of the radio station. That frequency is generated with a chopper, just like the chopper on the input of our switching power supply. When you turn power on and off quickly, you create a type of radio station. Just like your local AM or FM radio station, the chopper circuit we discussed yesterday is turning power on and off. If it does it quickly enough, it will broadcast that power through the air. Give it enough power and an antenna and you can broadcast for many, many miles. Or, you can do the same inside the chassis of your stereo equipment; something I am guessing none of us wants to do. Most modern switching power supplies run at reasonably high speeds: from 50kHz to 500kHz and make very good radio transmitters. Only, that's the last thing we want near our pure hifi equipment. Talk about pollution! Remember I said a good helping of skill and, what some consider black magic, is needed to quiet those transmitters and restrict their broadcast areas? Now you know why. And radiated emissions through the air are only half the problem. When you switch large amounts of power quickly, the energy of turning on and off has to come from and go to somewhere. That 'somewhere' is the ground of your power supply and that ground is connected directly to, you guessed it, your sensitive audio circuitry. But all hope is not lost for switching power supplies. The good news is this: their performance is wonderful. They are efficient, small, powerful and provide regulated low impedance power to circuits. They are a magnitude better performance in nearly every respect to that of a conventional supply. They are just noisy and hard to design. But there are talented people out there and some of the finest and quietest power supplies in the world are switching supplies. And yes, to answer the question lingering in your mind, they are better, far better than conventional supplies. Only...