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How to Calculate the Gain on an Amp With Multiple Inputs

An operational amplifier, or op-amp, is a piece of electronic circuitry that amplifies, or attenuates, a voltage signal. A summing op-amp is a special kind of inverting op-amp that takes multiple input signals and "sums" them into a final input before entering the op-amp. You use summing op-amps in audio mixer circuits. Another resistor connects from the input side of the op-amp to the output side. The gain on any op-amp is the ratio of output voltage to input voltage. For a summing op-amp, calculate the gain individually for each input signal.

Instructions

- 1
  Determine the resistance of the resistor directly connecting the input side to the output side of the op-amp. For example, it may be 10 kilo-ohms.
- 2
  Calculate the gain for each input signal individually by dividing the value of the resistor from Step 1 by the value of the resistor on the input signal. For example, if the input signal's resistor is one kilo-ohm, then divide 10 kilo-ohms by 1 kilo-ohms to yield a gain with magnitude 10. This means the output voltage signal is 10 times larger than the input signal.
- 3
  Multiply the previous result by negative one to get the true gain value for the op-amp. Because a summing op-amp is a kind of inverting amplifier, it converts a positive voltage to a negative voltage or vice versa. In this example, the true gain for the example input signal in the previous step is -10.

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