ABSTRACT
In the world of audio, amplifiers have many applications. They can be designed to amplify, equalize, combine, distribute or isolate a signal. They can even be used to match signal impedances between devices. A summing amp is designed to combine any number of discrete inputs into a single output signal bus, while providing a high degree of isolation between them. Power amplifiers are used to boost the audio output to a level that can drive one or more loudspeakers at their rated volume levels. Although most digital devices change the gain of a signal directly within the digital domain, it's also possible to change the gain of an analog signal using an external digital source. Much like the voltage-controlled amplifier, the overall gain of an analog amp can be altered by placing a series of digitally controlled step resistors into its negative feedback loop and digitally varying the amount of resistance that's required to achieve the desired gain.
