Getting it right

We started talking of transformers in yesterday's post, where I mentioned they had two main functions: isolation and getting the voltage correct. We covered isolation yesterday. Also a correction to yesterday's attempt at a brief and blanket statement. I was reminded by Ayre's CEO, Charley Hanson, that not everything that plugs into the wall has a transformer. He's right of course, as Charley often is (he's one of my engineering heroes). Light Bulbs, heaters, hair dryers, work directly off the voltage supplied to our homes. Not much in our hi fi systems does. Our equipment rarely needs as much voltage as supplied by the home's wall socket. We typically need less. That's where transformers come in handy. In fact, our homes need less too. When AC power leaves the generating plants the voltages are higher than what comes into your home—a lot higher. To ensure adequate voltage of 120 or 230 volts, power companies distribute energy at significantly higher levels, 10,000 to 100,000 volts. It is our old friend the transformer that reduces high voltages to usable levels in our homes. Those big power transformers that often sit atop utility poles, or in big metal boxes, perform the same duties that smaller ones inside equipment do. Most preamplifiers and CD related sources need only 25 to 50 volts, regardless of what they are fed. Power amplifiers need more, yet typically lower than what comes out of the wall, especially in 230 volt countries. Transformers use invisible magnetic fields to connect equipment to power lines. It is these same magnetic fields that determine voltage levels. Tomorrow I'll explain how these work and what we think of when designing a transformer.