balanced cables...
Balanced cables are often used for long runs as there will be less noise than using a standard instrument cable etc, but why are balanced cables better and how do they work?
As you may have seen a balanced connecter and cable has three conductors instead of two. Either a 'stereo looking' jack plug, or a three pin XLR connecter may be used for balanced connections. This is how it works:
When a signal is transmitted along a piece of wire, lets take a sine wave for instance:
It all looks fine until some noise is picked up, this can be anything like a signal induced by a nearby mains cable, or any other RF noise. Here is the signal with a spike of noise on it:
With an unbalanced cable in the example above the noise will be heard at the other end, at the mixing desk or studio recording device etc. The recording is ruined.
In contrast with an unbalanced cable two versions of the signal are sent along the cable this is why it has an extra wire:
These two signals are created by a 'line balancing transformer', or another circuit. The second version of the signal is 'upside down'. If noise occurs on the line as can be seen below, it will occur on both signals at once as they are both in the same physical cable:
However, at the receiving end is another 'line balancing transformer' or circuit that turns the second version of the signal up the right way again:
As the noise gets turned up the other way as well, the overall result is that the noise cancels itself out. This is because:
3+ -3 = 0
or anything summed with a number that is as equally as negative as it is positive, results in no change. And so the signal is clean:
A DI (Direct Inject) box is basically an unbalanced to balanced converter, it will take an unbalanced instrument lead and turn it into a balanced signal that can run for some distance to the mixing console etc. Mixing consoles or other equipment with balanced 'ins' have another transformer inside to convert it back again. This process of inverting one version of the signal can also be performed with some other circuitry.
You can buy a line balancing transformer here, better read the article on soldering though:
The End?