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Ground Loops - 3 - Unbalanced connections

How does the noise current get into the audio signal?

There are two main situations where this happens.

The first is in what are called 'unbalanced' systems.

You may be familiar with the terms balanced and unbalanced connections, but what do they mean? Well, consider any electrical system and you will see that it needs a complete path for current to flow, as in the ground loop. Thus the minimum requirement for connection between two items of equipment is two connectors, a send and a return.

Fig 3 is a diagram of an unbalanced system where two units are joined together. As you will see, there are only two wires between the two units. Thus the cable is made so that there are two connection paths as in Fig 4, and one of these also doubles as the screen. Now the screen in a cable is designed to protect the signal inside from electrical noise present in the environment, what is called RFI or Radio Frequency Interference. The screen usually consists of a metal braid or sometimes a conductive plastic that surrounds the cable within. In the unbalanced system, however, any interference signals will be passed straight into the audio signal, as the screen is also taking the return signal. An unbalanced connection will be made using either Mono Jack plugs or Phono connectors (Fig 5 & 6) and tend to be used in home or semi pro equipment. However, unbalanced inputs and outputs do appear on some pro gear, commonly on mixing desk aux inputs and outputs.

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