# Why is an inverting summing amplifier used in audio mixers?

• thereddevils
In summary, a summing amplifier is used as a mixer in concerts to combine different music produced by different instruments. The input voltages must be inverted in order to correctly sum them using the respective inverse input resistance or impedance. If the positive input is grounded, the output will be the negative of the weighted sum. If the input resistors feed the positive input, the result will be the opposite. Therefore, an inverting amplifier is used instead of a non-inverting amplifier for this purpose.
thereddevils
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 ?

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?

## 1. What is an operational amplifier?

An operational amplifier, or op-amp, is an electronic device that amplifies the difference between two input signals and outputs the result. It is commonly used in electronic circuits for amplification, filtering, and other signal processing tasks.

## 2. How does an operational amplifier work?

An operational amplifier typically has two inputs, a non-inverting input and an inverting input. The output of the op-amp is proportional to the difference between these two inputs. The op-amp uses internal circuitry to amplify this difference and provide a high-gain output signal.

## 3. What are the common applications of operational amplifiers?

Operational amplifiers have a wide range of applications in electronic circuits. Some common uses include audio amplifiers, signal filters, oscillators, and analog-to-digital converters. They are also used in instrumentation and control systems.

## 4. What are the important characteristics of an operational amplifier?

The main characteristics of an operational amplifier include high open-loop gain, high input impedance, low output impedance, and wide bandwidth. It should also have low offset voltage, low noise, and good stability.

## 5. Can operational amplifiers be used in negative feedback circuits?

Yes, operational amplifiers are commonly used in negative feedback circuits. Negative feedback is when a portion of the output signal is fed back to the input of the op-amp to control the gain and stability of the circuit. This allows for more precise and stable amplification of signals.

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