An amplifier, also called a summing amplifier, combines two or more signals prior to sending them to a single audio bus, signal processor, tape recorder track, or other destination. For example, on a mixer, if an aux send controls on all channels of a console feed a combining amplifier, whose output can be routed to a reverb system, cue or headphone amp, the monitor amplifier, etc. There are also devices which are active combining amplifiers, called an ACA, as well as passive combining networks