How does a fixed gain amplifier work?
Most all amplifiers are fixed gain. Some have a potentiometer in front to adjust the input level, which appears to change the gain, although all it does is change the input voltage. An amplifier works by using semiconductors in the form of transistors that can cause an output voltage or current to have a larger variation than the input voltage or current. They use DC power from a supply to do this. Usually several such stages are connected together to increase the gain, and feedback is usually applied to stabilize the gain and reduce distortion. True variable gain amplifiers use several techniques. One is to vary the operating point via a DC control voltage to change the gain. Another is to use a multiplier circuit, either digital or analog, to multiply the input voltage by a fraction that can vary between zero and one. .
