Ratios

Power transformers connect hi fi equipment to our home's AC wall sockets. Without power, we're back to the old Edison hand crank machines if we want to listen to recorded music. The voltages from wall sockets are higher than our equipment needs. In most countries that voltage is 230, the few exceptions are the United States and other countries in the Americas, along with Japan. The fact is, most modern American homes actually get 240 volts, but instead of applying the full voltage to receptacles, it is split into two: the AC neutral wire in the middle. This is how American and Japanese electric dryers and stoves can operate off of 240 volts, while the rest of the home runs at half that. Regardless of the voltage in your home's walls, stereo components typically need much less. To manage this we rely on our old friend the power transformer. Power transformers couple through invisible magnetic fields. To make an electromagnet, all you need is a coil of wire and some bits of iron. Wrap a coil of wire around a steel bolt, place a battery between the wire's two ends and you can pick up metal objects with the resulting magnet. A transformer isn't much different. Power transformers use two coils of wire wrapped around metal pieces (called laminations in one type of transformer). The first coil connecting to the AC wall receptacle is the primary, the second coil of wire is...wait for it... ...the secondary. Wire is wrapped around the metal. The number of times the wire is wrapped around is called the turns (how many times the wire is turned around the metal). It is the ratio of turns between the two coils of wire that determines the voltage produced. Identical turns equals identical voltages. 100 turns of wire on the primary, in contrast to 100 turns of wire on the secondary, produce a 1:1 transformer. 120 volts in, 120 volts out. But change those ratios and change the voltage. More turns on the primary vs. fewer turns on the secondary and voltages are reduced on the transformer's output. And the opposite is also true. The amount of power transferred between the wall and the equipment depends on bulk. Bigger, thicker wire and metal pieces transfers more energy than the opposite. Which is why a power amp transformer is bigger and heavier than a preamp transformer.