A summing amplifier is an electrical circuit layout that allows for the addition of more than one signal, creating a sum of all the circuits combined. The idea behind it is to incorporate multiple sources of input, while keeping each source separate to avoid one of the input sources affecting another. The amplifier allows the user to achieve a voltage sum at output that is calculated at the same rate mathematically as all of the input sources added up. Essentially, this means the amplifier creates an operational amplifier because when more than one input voltage is entered into a circuit and added together through the course of the circuit, the output voltage is a constant of the sum of all of the input voltages.

When a circuit is needed to connect two different microphones to one amplification source and the user wishes to hear both of the microphones through the same source, the circuit used as the microphones are plugged into the amplifier is a simple form of a summing amplifier. The signal coming into the amplifier from both microphones is able to be heard through the same speaker simultaneously due to the summing amplifier being created. The use of a summing amplifier is required for any audio mixer machine to function properly because it must be able to receive signals from multiple sources at the same time and let them all be output through one source after being mixed by the user as the signals pass through the circuit.

Another use for this type of amplifier is in applications that require signal conversion. In any device that performs the function of converting an analog signal into a digital one or vice versa, a summing amplifier is used. The amplifier allows for converting a binary number generated by the input signal to a digital voltage.

Whether it is realized or not, there are more common electronic devices that utilize summing amplifier circuits as they perform their other primary functions. Any time one or more signal or voltage is being input to a device and the device only has one output, the circuit within the device is a summing amplifier circuit. These types of circuit formats are also used in devices that are related to different types of currents. Both AC and DC currents can be input to a summing amplifier circuit to output a constant voltage or signal.