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XLR Connectors

Interconnect


Are you normalled? Or have you ever wondered if you should invest in conductive plastic? Do you find your creative energies sapped by leads that consistently fall apart? If so, take heart, for in this series, we'll see how to make up leads the professional way, look at the pros and cons of various connectors, investigate the products of different manufacturers, and discover the best cables for each job. We'll also discuss such things as cable testers, patchbays, adaptors, racks, looms, impedance matching and all the other mysterious aspects of interfacing technology.


History and Usage



The XLR connector originated from Cannon Electric in the USA two decades ago. For this reason, XLRs are also widely known as 'cannons', but today they're made by several manufacturers, and in any case, Cannon subsequently became part of ITT.

The name 'XLR' was originally coined as a mnemonic for a pin wiring sequence adopted in the 60's, where X represented Earth (Pin 1), and L and R stood for Left and Right, which were pins 2 and 3 respectively. Along with the Jack, the XLR has become the principal connector for professional sound use. Although available with 4, 5 or 6 pins, the 3 pin version is the universal standard for making connections from microphone through to speakers.

Unlike more common 'consumer' connectors, the XLR cable plug comes in both male and female varieties, as does the chassis socket. Most manufacturers use the female socket for inputs and the male socket for all outputs, so the corresponding input and output plugs that are part of your leads are male for going into inputs, and female for interfacing with outputs.

However, some old equipment from the USA may use the opposite standard, with female (chassis) sockets for outputs, and vice-versa. As this is contrary to modern practice and can cause endless confusion, equipment with this configuration is best modified if at all possible.

Confusion also arises from alternative terminology, especially over the phone, or when asking a colleague to pick up a lead on the other side of the room. [Wrong]doers here are people (and catalogues!) which call female cable plugs 'free sockets', and a male chassis socket a 'fixed plug'. If we all stick to calling things that dangle on the end of leads plugs, and then distinguish the sex (ie. Male for a plug with pins), there shouldn't be any need for mistakes.

If you like to use alphanumeric codes try the Switchcraft system: A is for cable and D for chassis connectors, with M for male (pins) and F for female (socket contacts), and lastly a number between the two letters to indicate the pin count. So, for example, the standard 3 pin cable connector at the mic end of a lead is an A3F, whilst the connector on the actual microphone will be a D3M.

A great advantage of cannon leads is that with plugs of opposite sex at each end, cables can be readily extended, by simply plugging them together in a line. Also, lots of short-leads can be stored in-line, on a cable drum — it saves a lot of frustrating entanglement.

Standards



Like other connectors with lots of pins (notably the notorious DIN) cannons reflect the diversity of human ideas, with their connections being wired in every conceivable configuration despite the existence of a standard (BS 5428), which arrived too late, and had little cognisance of previously existing practice in the music business. Asa result, the alternative American mode of wiring (Pin 3 = hot) has persisted, even in the UK, where it was originally used to satisfy export requirements.

Referring to the diagrams, these show the BS5428 and then the alternative (USA derived) standard for unbalanced and balanced lines respectively, plus a stereo connection using a single 3 pin plug that's often encountered.

To put matters in perspective, because 3 pin XLRs don't (unlike DINs) generally get involved in two signals travelling in different directions (ie. send and return); the standards apply uniformly to all interfaces, be they on tape machines, mixers, DI boxes or transducers (DINs have several idiosyncrasies in this respect), and so the confusion over standards doesn't hinder too much; particularly as most large scale manufacturers have adopted the BS5428 (Pin 2 = hot) connection, and also avoid using three pin cannons for stereo.

From time to time of course you will come across equipment with the USA standard, but in most instances, the internal wiring is readily modified, sometimes by simply changing PCB links. When ordering new equipment, ask about the wiring. If it's incompatible with your own leads, it's usually possible to have the XLRs factory wired to conform before the equipment is despatched and often at no extra cost.

If you look carefully at the accompanying diagrams, you'll see that pin 1 on XLRs is always connected to the cable screen or ground. This is not purely coincidence — pin 1 is designed for this purpose, being longer than the others, thus ensuring it's always the first to mate and the last to be disconnected. In practice, this means the cable screen is being connected before the other conductors ensuring there are none of the loud buzzes, crackles and bangs that occur when lesser connectors are inserted or removed from 'live' equipment.

Advantages



The advantages of XLRs over other competing connectors are essentially threefold:

1) They're made to a very high standard. Those by original manufacturers like ITT — Cannon and Switchcraft are physically very robust, have excellent electrical contacts to boot, and with adequate care, can be expected to work without trouble for years.

2) They accept a wide range of cable diameters — even up to 1cm square speaker cable — whilst maintaining solid clamping.

The Neutrik and Switchcraft types being particularly adept in this respect.

3) With large and widely spaced 'solder bucket' terminals, it's easy to make solid, reliable solder connections inside XLRs, even for those of you with gorilla paws when it comes to wielding a soldering iron!

As you might expect, connectors of this calibre attract a price to match, but at the same time, budget XLRs, made to lower standards than the originals, are available. Whilst it's important to recognise that these cannot match the longevity, of an ITT-Cannon XLR, they're certainly a welcome alternative to struggling with DIN plugs!

Which Product?



Going into detail on the advantages of each brand, ITT-Cannon XLRs are the most expensive, but they do feature rubber insulation on the female inserts, making them very durable. Spare parts are also available from studio suppliers, so plugs with missing or damaged parts can be cheaply repaired. ITT-Cannon also do a cheaper series which has a plastic, rather than rubber insert on the females.

Apart from the tendency for the hard plastic inserts to shatter, Switchcraft XLRs are also the 'bee's knees', and they're less pricey too. One plus point is the captive assembly screw, which means one less part to go astray, and another is the exemplary cable clamping which is especially good on thin leads. Perhaps most important though, both the ITT-Cannon and Switchcraft types are built to very close tolerances; problems with physical compatibility are almost unknown when the two are mixed in a system.

Neutrik XLRs can be obtained at around half of the ITT-Cannon asking price. The inserts are made from a soft, easily melted plastic, and the general standard of materials and tolerances is lower. As a result, a Neutrik connector will occasionally jam solid when mated with a Switchcraft. Despite these objections, the cable clamping is excellent, and avoids fiddly screws altogether. Some Neutriks are available with gold-plated pins for enhanced sound quality on low level signals.

Cheaper still are oriental copies of XLRs, which often look like the top grade devices to the inexperienced eye. Although the home studio environment doesn't place too great a demand on ruggedness, so making these budget types admissible, beware of possible mating problems resulting from poor tolerances. Cheap XLRs will also demand more care and attention but equally, it would be silly to waste precious funds on 'Rolls-Royce' XLRs (ie. Switchcraft, ITT-Cannon) except in special instances where there'll be lots of plugging and unplugging going on.

So far, we've looked at 3 pin XLRs. The 4 and 5 pin species crop up occasionally, usually for dedicated control cables, or for linking intercoms or remote power supplies, so the wiring tends to be a law unto itself. Although most studio gear has separate 3 pin XLRs for stereo outputs (or even a single 3 pin), BS5428 specifies the 5 pin XLR for stereo — so the connections are shown just in case you ever come across it.



Previous Article in this issue

Home Studio Recordist

Next article in this issue

Dynamic Noise Filter


Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.

 

Home & Studio Recording - Sep 1983

Feature by Ben Duncan

Previous article in this issue:

> Home Studio Recordist

Next article in this issue:

> Dynamic Noise Filter


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