Unbalanced / Balanced Plugs.

How an unbalanced mono plug is connected to a one-conductor shielded wire. Or, in other words, to a wire that has one internal conductor which is surrounded by a shield, that also functions as the ‘ low ’ side for the audio signal.
The same fi gure also shows how an unbalanced stereo plug is connected to a two-conductor shielded wire. That is, to a wire with two internal conductors, both of which are surrounded by a shield. The two signals are discrete, but share a common ground.
The two signals could be left and right of a stereo signal or they could be two totally unrelated signals, so the nomenclature of ‘ stereo guitar plug ’ is ubiquitous, but not really accurate. Hopefully, with the aid of the previous picture, you now have a clear concept of how unbalanced audio is connected. The same rules apply whether you are using guitar plugs, RCA plugs or whatever the ‘ plug dejour ’ happens to be today.
But what about balanced audio? Why is it called ‘ balanced ’ , and how does it differ from an unbalanced signal? This is where we come to some very clever voodoo.

Balanced audio is created by splitting the audio signal into two separate but equal parts, and then inverting (flipping) the phase of one of the two.
Your instantaneous question may be ‘Why bother?’. The reason is that when the in- phase and the out-of-phase signal are properly recombined (by uninverting the flipped phase side in a particular way), the result is that our desired audio signal is not only amplified, but any stray noise it has picked up is immediately nullified, leaving only the pure signal.
This is such an important concept that I’m going to repeat it in different words, hoping that it will embed itself deeply in your minds.

Balanced audio reduces or eliminates unwanted noise picked up in wires by flipping (inverting) the phase of one of the two conductors that carry the signal. When the signal is properly recombined, its amplitude (volume) is increased and the unwanted noise is nulled out.Yet another way to describe this is that when the plus (+) noise is summed (added) to the minus (-) noise, the result is no noise. Or at least very little noise.

What this means is that balanced audio runs can be hundreds of feet long without degrading the signal by adding noise to it. Pretty cool, huh?
Figure 2.3.6 shows a balanced mono guitar plug, and also the noise cancelling concepts we’ve talked about above. Pay particular attention to it, as the subsequent discussion in this section is based on you having a clear understanding of how balanced audio works.
Hopefully, I ’ ve now tossed this information at you in enough different ways that you’ve got a decent grasp of it. Let’s put it in still another way.
Balanced audio lines help cancel out interference of many types. Not only hum (ground loops), but also buzz (60 Hz harmonics), thermal sound (white noise), digital clock jitter and lots of other bad stuff, too numerous to mention.
Next up is an example of a typical balanced  +4 dBu audio connection, the kind of connection you might make from a pro-level recording console to a pro-level audio recorder – analog or digital. This example is shown in Figure 2.3.7 for an XLR type (three-pin) connection.
You don ’t have to pay too much attention to the voltage values – they represent an ideal you might see on your DVOM, on a clear day with a favoring tailwind.
The only function of the voltages in this diagram is to give you some idea of what you might encounter in the real world, and reinforce the concepts of balanced audio.
With luck – and attention on your part. you’ve now seen the advantages of balanced audio. You will restrict your unbalanced connections to short runs and, if given the option, always wire gear in balanced mode, right?

Now we come to the real mind-blowing part. Electrical power is basically an audio frequency signal! We’re all painfully familiar with the sound of 60 Hz hum. it’s ubiquitous. No matter where you go, you hear it – anywhere within the AC power grid, and often up to several miles away from it.
But is our regular run-of-the-mill 120 V, 60 Hz electrical power distributed in a manner similar to balanced audio in a studio, to reduce noise pick-up? No! Regrettably, all standard 120 V power distribution systems are wired in an unbalanced mode – this makes them highly susceptible to picking up all kinds of crud!
Every time you hear 60 Hz (or any other noise) in an audio system, it’s
degrading the sound quality and robbing your amplifiers of power.
This brings us to our next section in this module. The truly observant among you noticed that the last fi gure included a credit to something called Equi=Tech. In the next part, you ’ ll fi nd out why that mysterious credit is there. Can you wait that long?