Balanced and Un-Balanced Cables

This page is our attempt to answer one of the most commonly asked questions we get through our e bay and online shop. “Do I need balanced or un-balanced cables? And can you tell me the difference?”

Unbalanced signals

Unbalanced signals are easy to explain: they are normally transmitted along a pair of wires - the signal, and the signal ground. Thus, the signal consists of a continually varying electrical voltage, with respect to its ground. Typical examples are the connection from guitar to amplifier, or the interconnects of a domestic hi-fi system.

The big problem with unbalanced signals

The world would be a lot simpler if we could use unbalanced signals for everything. However, they have one big, no, massive drawback: interference. As you can imagine, unbalanced signals pick up interference from electrical devices in the vicinity. Over short distances (under 10 metres) you might not notice, but over longer distances, not only does the interference become more noticeable, but signal degradation will occur. 

Balanced signals

So, unbalanced signals are transmitted along a pair of wires, but are susceptible to interference. The answer? Go balanced! In a nutshell, a balanced signal is the same as an unbalanced signal, but with the addition transmission of an anti-phase signal (think mirror image). That is, a balanced signal is transmitted along three wires (aka 3-pole) - the signal (known as +ve or in-phase), the signal ground, and an anti-phase (-ve) signal. Typical examples are microphones, outputs of mixing desks, DMX transmission lines, etc.

Now the science bit...

Let's think of how electrical interference affects an unbalanced signal: put simply, it adds electrical noise to the signal which can be usually heard as a buzzing noise. Now, a balanced signal is affected by the same interference, but (and it's a big 'but'), because the balanced signal has a 'phase' and 'anti-phase' version of the signal, the interference affects both signals equally. The clever bit is done by the balanced input stage of your equipment, where the phase and anti-phase signals are processed by a differential amplifier circuit that is able to reject the electrical interference (known as common mode noise rejection). 

A balanced signal path consists of three parts...

The most important thing to remember when dealing with balanced signals is that you need three parts: the balanced output (e.g. microphone), the balanced cable, and the balanced INPUT (e.g. mixing desk). If any of these three parts is missing then you will (at best) default to unbalanced mode. If you connect a balanced output to an unbalanced input, you will always have an unbalanced signal path. If you use an unbalanced cable with a balanced input and output you will always be unbalanced. You can convert an unbalanced signal to a balanced signal using a D.I. box.

What does this mean for cables and connectors?

To recap, unbalanced signals require two wires to transmit a signal, whereas balanced signals require three wires. Starting to ring any bells? Yes, this is the reason why your microphone cables use 3-pin XLR connectors. Conversely, your guitar leads use mono (2 pole - Tip and sleeve) jacks. It's not just the connectors, however. A balanced signal needs three wires - +ve signal, -ve signal and screen - hence the reason why your microphone cable has two cores, plus a screen.

XLR connectors

Nearly every XLR connector manufactured is a 3-pin connector - that is, designed for use with balanced signals.

Jack plugs

This is where things start to get a little more complicated. You've probably noticed that jack plugs come in two varieties - mono and stereo. These are also commonly known as TS (Tip/Sleeve) and TRS (Tip, Ring, Sleeve) which describe the electrical contacts of the plug. It won't take much to realise that a TS jack is an unbalanced connector, whereas a TRS jack is a balanced connector. 

RCA Phono plugs

These connectors consist of a central tip, and a sleeve. They are unbalanced. If you have any Semi-Pro or Pro playback equipment (CD players, mini disc players, etc), you might well have two sets of outputs on the back - one set on phono plugs, and the other set on XLRs - making sense now? (ph>

The XLR to Phono cable

This cable has an XLR connector (balanced) at one end and a phono plug (unbalanced) at the other.

This cable is actually transmitting an unbalanced signal (this is always the case as it is using the 2-pole phono connector). At the XLR end, Pin 3 (which would be the anti-phase signal) is connected to Pin 1 (signal ground). This is done simply to ensure that it is not left 'floating'. The circuitry of 99% of balanced inputs and outputs has been designed to co-operate with this wiring scheme. Hence you are able to connect the unbalanced outputs of your CD player to the balanced inputs of your mixer. Please note that the signal is NOT BALANCED! In certain circumstances (especially with old equipment) the input/output circuitry is not designed to work with Pins 1 & 3 connected. In this case, it is normal practice to leave Pin 3 (the anti-phase signal) unconnected (floating).