3.9 : Design Example: Vintage Mixing Console

A sound engineer at a music company recently encountered a problem. The output from their newly acquired studio's vintage mixing console was too low for the requirements of modern recording equipment. To rectify this situation, the engineer decided to design an audio pre-amplifier using an operational amplifier (op-amp) to boost the signal level.

The specifications for the pre-amplifier were clear. It needed to amplify the audio signal by a factor of 10, have an input impedance above 10 kilo-ohms to prevent overloading the console, and be capable of covering the entire audio spectrum from 20 Hz to 20 kHz.

The engineer chose the op-amp model 741, a popular choice in audio applications due to its ability to handle the required frequency range without significant gain loss. This model would ensure that the pre-amplifier could adequately amplify the signals across the whole audio spectrum.

To meet the requirement of a gain of 10 and high input impedance, the engineer decided to use the non-inverting operational amplifier configuration. The gain of a non-inverting amplifier equals one plus the ratio of the feedback resistor to the resistor connected to the inverting input.

To achieve the desired gain of 10, the engineer selected a 100 kilo-ohms feedback resistor and a 10 kilo-ohms input resistor. This combination would provide the necessary amplification while maintaining an adequate input impedance to prevent overloading the mixing console.

This carefully designed pre-amplifier effectively boosted the console's output, enabling it to drive the digital recording equipment successfully. The result was a seamless integration of vintage and modern equipment, ensuring the preservation of the unique sound qualities of the vintage console while taking advantage of the capabilities of contemporary digital recording technology.