2.3 Balanced and unbalanced audio and AC power 97

If the sine wave repeated this action 1000 times in a second, we ’ d say it has a frequency of 1000 Hz (hertz) or, in older terminology, 1000 cps (cycles per second). We audio folks got tired of saying ‘ see-pee-ess ’ and renamed the unit of measurement ‘hertz’ as it ’s shorter.

Higher frequency sine waves will appear more squished together horizon-tally; lower frequency sines will look more spread out. The reason for this is that the horizontal axis in an oscilloscope is the ‘ time base ’ – it shows the progression of the waveform from the past into the future. The more times a signal reverses polarity, the higher its frequency and the more reversals present in a given period of time.

All sound (almost) is made up of complex combinations of AC (alternating current) waveforms, most of which are not sine waves. The only exception is a DC (direct current) pulse, which will make a one-time ‘ click ’ when connected to a speaker or headphone, but not much else.

We use sine waves for measurement because they ’ re easy to quantify.

I hope you are now fi ne with sine, as it were, and ready to see how this applies to real-world situations.

There are only two ways that an analog audio signal can be carried along in a wired connection. For the sake of brevity (and sanity – mine), I ’ m not going to expound on digital or RF transmission of audio.

The simplest way for an audio signal to be carried on a wire is as an unbalanced signal. This means that there is a center conductor (hot), and (typically) shield and ground are combined in the outer layer of the wire. So half of the signal path is (sort of) shielded by the outer layer, and the outer layer itself is tragically vulnerable to interference from sources in the outside world.

What this means is that unbalanced audio is basically limited to runs of 20 feet or less, and even then it lacks the ability to null out induced noise, hum and the other crud we encounter with great ah, frequency.

Balanced audio, on the other hand, can survive runs of hundreds of feet, so all pro audio facilities use balanced mic lines, balanced transmission lines, and do most of their internal wiring in a balanced manner.

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Audio Wiring Guide98

We ’ ll explore what unbalanced/balanced wiring is after we take a quick peek at a couple of guitar plugs to show you the physical difference between balanced/unbalanced connectors.

I ’ m going to recycle some pictures here from Section 3.1. And being lazy, I ’ m also going to recycle some of the text, as I worked very hard to make the differences clear, and cannot fi nd any way to make things more lucid than what I ’ ve already written.

What you ’ ll see next are the solder tab ends of a stereo and mono guitar plug, followed by the ‘ business end s of the plugs that actually get inserted into guitars, amplifi ers and other gear. And if you guessed that the mono plug is unbalanced, while the stereo plug can be wired balanced, you get a gold star!

There are always caveats and this example is no exception. The so-called ‘ stereo ’ guitar plug can be wired as a single balanced connection, or two unbalanced mono connections that share a common ground. So don ’tassume, always check.

A close-up of the two solder tabs on a stereo male guitar plug is shown in Figure 2.3.2 . I ’ ve drawn two arrows to show exactly what part(s) I ’ m talking about. The longer part, that extends to the upper left in this picture, is both a strain relief for the wire and the part that the shield/drain gets soldered to.

Let ’s call the two tabs I show the ‘ upper ’ and ‘ lower ’ tabs in this picture. The lower tab goes down to the tip of the plug. It ’s the high/hot conductor.

Figure 2.3.2 Solder tabs of stereo male guitar plug.

2.3 Balanced and unbalanced audio and AC power 99

The upper tab goes to the ring of a stereo plug, but is omitted (not present) in a mono plug. It ’s the low/cold conductor. As a general rule, tip is high, ring is low, and the long barrel of the plug is used for drain/shield.

Since I want everyone to be totally clear on the difference between stereo and mono plugs, I ’ ve got a couple of side-by-side comparisons ready.

These pesky plugs are so shiny I had to put some white artist ’s tape behind the solder tabs, so you could see them against the strain relief behind them ( Figure 2.3.3 ). I hope it ’s all clear. On the left is a mono plug with one tab. On the right, a splendid example of a stereo plug with two solder tabs.

Now that we ’ re straight on the tabs, let ’s see the whole plug ( Figure 2.3.4 ). Here we can see the business ends of our plugs – mono on the bottom and stereo on the top. Notice the ring on the stereo plug? That ’s the part the low conductor is connected to – and is clearly omitted in the mono plug below it. So one tab � no ring, mono plug. Two tabs � has ring, stereo plug. And remember, a ‘ stereo ’ plug can be wired as unbalanced stereo or balanced mono – the wiring will look the same.

Figure 2.3.3 Mono/stereo comparison – 1.

Figure 2.3.4 Mono/stereo comparison – 2.

Audio Wiring Guide100

Figure 2.3.5 illustrates 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.

Simplified guitar plugs

Dashed cylinders are shield of wire

Unbalanced mono

Unbalanced stereo

Signal 1

Chassis/earth ground

Chassis/earth ground

Signal 2

Signal 1

Figure 2.3.5 Unbalanced guitar plugs.

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 de jour ’ 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 (fl ipping) the phase of one of the two.

2.3 Balanced and unbalanced audio and AC power 101

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 fl ipped phase side in a particular way), the result is that our desired audio signal is not only amplifi ed, but any stray noise it has picked up is immediately nullifi ed, 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 fl ipping (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.

Figure 2.3.6 Balanced connection/noise cancellation.

Simplified guitar plug

Dashed cylinder is shield of wire

Balanced mono

Normal wavewith noise

�Normal wave

with noise

Normal wavewith noise

�Inverted wave

with noise

Noise cancellation

Chassis/earth ground INVERTED Signal

Normal signal

Signal 1

Signal 1

� �