Why is an inverting summing amplifier used in audio mixers?

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An inverting summing amplifier is preferred in audio mixers because it effectively adds multiple input signals while inverting their phase, which is crucial for maintaining signal integrity and preventing distortion. The input voltages must be inverted to ensure that the output represents the weighted sum of the inputs, allowing for proper mixing of different audio signals. This configuration also simplifies the design by grounding the positive input, which stabilizes the circuit. Using a non-inverting amplifier would complicate the mixing process and could lead to phase issues. Therefore, the inverting summing amplifier is essential for accurate audio mixing in live performances.
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why is an inverting amplifier and not a non-inverting amplifier used as a summing amplifier ?

Why must the input voltages be inverted in a summing amplifier ?

I am told that a summing amplifier is used as mixer in concerts where different music produced by different instruments go through this summing amplifier before being amplified to the audience. Shouldn't the input by different instruments be the same as the output ?
 
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thereddevils said:
why is an inverting amplifier and not a non-inverting amplifier used as a summing amplifier ?

Why must the input voltages be inverted in a summing amplifier ?

I am told that a summing amplifier is used as mixer in concerts where different music produced by different instruments go through this summing amplifier before being amplified to the audience. Shouldn't the input by different instruments be the same as the output ?

anyone ?
 
A summing amplifier adds voltages weighed by their respective (inverse) input resistance (or impedance) with repect to ground.

We can see that this can work when the positive input is grounded and the output is the negative of the weighted sum.

Now try the same thing with the input resistors feeding the positive input. What do you get?
 

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