What are practical applications of a transformer coupled amplifier?

Answer 1

Well the purpose of the transformer in an amplifier is impedance matching. Lets say the transformer is on the input of a audio amp. Now the amp circuitry has an input impedance (this is important because matching the impedance gives us maximum power transferred from the input signal source to the amp circuit, and that increases performance) and a microphone has an output impedance. So if the microphone is 10,000 ohms and the amp circuit is 500 ohms then the transformer is designed to transform 10,000 ohms to 500 ohms for better signal transfer. If the trans former is on the output of an amplifier the trans former transforms the output impedance of the of the power amp circuit to the input impedance of the load. If the output is a speaker (usually 8 ohms ) and the output impedance of the amp circuit is 1000 ohms then for maximum power transfer the transformer trans forms 1000 ohms to 8 ohms. This was the case using electron tubes. Now with transistors, amplifier circuits can be built with lower output impedances (common collector circuit in a class B power amp) so the costly transformer can be eliminated. Also Audio Transformers are made slightly different in design than power transformers. Ausio transformers are designed with higher resistance in the windings to enable a wider frequency response where as power transformers are designed with much lower resistance to keep heating minimized while passing only one power frequency (60 hertz) at large amounts of power. Roger nsc@psu.edu