Leaving Class A — Nelson Pass / 2008

The meters on our amplifi ers are different. They refl ect the current consumption of the amplifi er, and when the amplifi er is operating, they don’t go down to zero like the meters on other amplifi ers. This is because the electrical current consumption of our circuits has a fairly high value at all times, a property called the bias. The bias current runs through the amplifi ers at a minimum value, determining the class of operation – Class B, Class AB, or Class A. Class B has no bias current, Class AB has a moderate bias current, and… More...

Power Supplies — Nelson Pass / 2001

Lots of people don't understand electricity, but they do understand plumbing. Hydraulics provides a good analogy in understanding basic electrical flow. Wire is a pipe. Water pressure is voltage. Water flow is electrical current. Lakes and storage tanks are capacitors. Diodes are one-way valves. Tubes and transistors are faucets. The entire power circuitry of an amplifier can be seen as a community water system. The sun, driving the weather cycle, deposits water on the landscape, and it collects in a lake behind a dam. The community draws water as needed through pipes. In the winter, the rain collects in the… More...