Dismissing all myths and legends, Simon Bateson expounds on the importance of cables and connectors to the modern musician.

The hi-fi press and, to an increasing extent, recording/PA magazines give very serious coverage to the honourable subiect of leads, or to give them their correct modern title, 'interconnects'. In this series of articles, I would like to give some pointers on what is, and what isn't, important in an area that has become riddled with superstition and profiteering. As a preview, and to give an idea of my political stance on cables so that people with widely differing approaches may gird their loins for battle, I will summarise the main ideas to be explored:

- Leads need to be reliable, it is a well-documented fact that cables and connectors are the most unreliable components in any electronic system.

- When fed from a signal with a significant source impedance, such as a guitar, leads should have the correct total core/screen capacitance.

- If used in balanced or noise-rejecting applications, leads should be made from the right type of cable and be correctly connected at each end.

- There is no such thing as directional cable, magical cable or cable that (having attended to the above points) makes your sound better. Anyone who tells you anything else is a charlatan, after your money by dishonest means.

KEEPING CONNECTED

A cable is almost always terminated by a connector of some type, and these connectors do not have a happy time of it on stage. The venerable and commonplace jack plug was never designed for stage use. Developed as a connector for headphones, it has evolved from what is now termed the 'bantam' or 'B gauge' jack, which itself was designed for the early manual telephone exchanges. For exchanges, the plug had to be compact and reliable, as well as easy to insert and remove. The modern bantam plug, still used on professional patchbays in standard (316) and miniature (4.4mm) forms, costs around £3, as do the sockets — cheap jacks and sockets cost around 40p!

The ordinary quarter-inch jack has two major weaknesses for stage use. The first is that the cable clamp is almost always pretty useless. I have spent many hours and plugs contorting flimsy grips to try and hold the cable, even melting them into the insulation at one time! At the moment, there are two plugs that really do overcome this problem — at a price.

The first is the Neutrik NP Series jack, which uses a large barrel and the same compressed ridged collet as Neutrik's rather nice XLR connectors (of which more later). This plug needs a fairly beefy soldering iron to attach the earth wire properly — the usual 15W iron will have problems. With good soldering, the outer casing and collet clamp goes on easily, and it's built like a little tank. The second plug is available through RS/Electromail, in stereo form as 208-3704. Why did the the mono version, 477-983, get discontinued? And why does the stereo version cost £4.90 plus VAT? If you can stand RS's sense of humour in the price department and are fairly neat at assembly, this plug makes a compact and solid termination to 3-5mm cable. It's highly recommended for headphones.

If you really must use nasty cheap plugs, the only thing you can do is rely on the strength of the screen for retention, not the clamp, and allow plenty of slack in the centre core connection. An interesting problem with many 'noiseless' guitar cables is that most people — and some companies! — don't know why the inner insulation is black so they just strip it as usual, allowing a little bit of squidgy black outer material to trail between core and screen with the result that the poor guitar (or whatever) runs into an almost short circuit! The black coating on the inner insulation conducts so it must be peeled back to ensure none of it touches the centre core. My suggestions for assembling jacks are summarised in Figures 1 and 2. If you find the cable is too butch and chunky to fit the plug, don't force it and hope — maybe your cable/plug budget needs re-proportioning!

As for the multitude of 'chunkier' jack plugs around at the moment, well, I would just take the top off and examine the innards. It's worth mentioning that Maplin is selling a metal-cased jack plug at present, code HF87U, with a rounded barrel end, which by some aberration actually has quite a big cable clamp! I don't expect supplies to continue, good things never do. It's still not as good as a Neutrik, of course. At least, we don't have to discuss that living phlegm, the phono plug, because none of you ever have to deal with it. Do you...?

What's the second problem with jack plugs? Well, they stick out quite a long way and break off (or break the socket) when you bang them on things or abseil off the stage using your guitar lead. The only answer to this one is: be careful. By all means, wrap the lead round a guitar strap, but remember that if you wrap it round the amplifier handle, or use locking jack sockets as well, there could be a big accident when you finally trip over it. It's better to be disconnected for a few seconds than for the whole night. For guitars with sockets on their edges and for effects pedals everywhere, Neutrik also make a well-damped side-entry jack plug.

EXTRA LOW RESISTANCE

The XLR, or eXtra Low Resistance, connector was originally developed for laboratory equipment where the connector had to carry heavy currents and not affect the signal by contact resistance. The usual 3-pin XLR connector is rated to carry 16A at 250V AC and has a typical contact resistance of 0.003 Ohms. You can't use them for the mains, because they are not childproof; you shouldn't really use them on speakers, because of the danger of mistaking a lead and frying a microphone amplifier. These are not electrical limitations; the XLR is a solid and well-rated connector, with a large contact area, which is wiped clean with each insertion.

The most widespread early models were made by Switchcraft and ITT-Cannon, hence the term Cannon connector. They use a silly cable clamping arrangement, in which small and easily lost grub screws press on small and easily lost metal shells, which in turn press on a (usually perished) rubber sleeve. To remove the shell, you have to turn another screw anticlockwise whereupon it moves forward... this confused everyone so much that when Neutrik's XLR plugs arrived they marketed themselves. British manufacturer, Deltron now use the same collet clamp system as Neutrik, so look out for them as well — they make a 'silent' switched jack plug, which is very useful for guitar leads. The only remaining apparent advantage of Switchcraft connectors is that the insulation is resilient so they are more resistant to breakage. I don't know how important this turns out to be in practice. What is more important is that during the '70s and '80s, there was some disagreement among manufacturers as to the meaning of the pin numbers, which resulted in lots of out-of-phase signals.

Just in case you were wondering:

Pin 1 is arranged to connect first and is always ground or common.

Pin 2 (on the other side) is positive phase on balanced signals and signal on unbalanced systems.

Pin 3 (in the middle, of course) is negative phase on balanced signals, and unused or grounded on unbalanced systems.

"There is no such thing as directional cable, magical cable or cable that... makes your sound better. Anyone who tells you anything else is a charlatan, after your money by dishonest means."

PERFECT MATCH

There are a number of application areas for cable. No single cable type suits all applications perfectly. The major audio applications are: studio installations, stage/PA cables, instrument cables, and multicores.

Studio Wiring

When wiring a studio, you will want a cable that is very easy to terminate, since you may have hundreds of plugs to fit. It should be compact, lie properly in bundles, and have good screening and fairly low capacitance. It does not need to be very flexible or rugged or be multicored, since much will run in trunking, to and from many different points. All these factors point towards cable such as Canford's 'FST' foil screened twin — but this cable is specifically not recommended for stage use! Foil screening and small-gauge cores, in particular the cheaper cables such as Phonoflex, will not put up with the repeated stretching and twisting experienced by instrument cables, so don't use it.

Stage and Studio — Single Leads

On-stage, the overriding requirement is for toughness and reliability. The mechanical structure of a cable does vary significantly between makes and types. The strength of the jacket depends on thickness and material — synthetic rubber is good but rather heavy, and polyurethane is very hardwearing, but plasticised PVC is the most common type for leads and multicores. Some cables are specially designed for slinging between beams without sagging and have a high tensile strength imparted by a core of Kevlar, but of course, these 'catenary' leads have no strength at the plug — they need attachment with a proper 'curly anchor' or by tying the cable back to itself. For real strength, you need to strip the cable back from the Kevlar and tie it to a hook, but perhaps that's going a bit far!

The outer jacket, besides giving the cable protection, should also make it easy to coil up after use. The core will be made from a large number of fine wires, for flexibility rather than for current carrying capability or strength, while the screen must be made from braided or double-lapped copper. I know that some cables are marketed with conductive plastic screens and drain wires for instrument applications, but they are just not reliable enough. One of my prized exhibits is a cable that came free with a rather cheap guitar, which looked like screened cable. It was of circular cross-section and seemed to have inner and outer conductors. It never worked very well, and when dissected, the 'screen' was just a few copper strands run along one side of the inner core rather than wound around it! What a great idea. If you ever find a lead like this, put it in the bin.

Within a studio environment, leads can also take some punishment. Have you noticed that, when sitting on a chair and playing the guitar, the lead always ends up under the chair leg? Why is that? Meanwhile, back at the patchbay, leads really can suffer, and in professional studios, the very best and most expensive cables and plugs are used for the patchbay.

Guitar Leads

Guitar cables have one demand placed upon them, which is unknown to most people and is different to just about every other application — the need for the correct core to screen capacitance. The reasons for this, and the entirely new problems that come about from beltpack radio transmitters, will be discussed later in the series. In most other respects, guitar leads have the same requirements as any other single stage lead. Don't use locking connectors! Try cables such as Canford HSS or Maplin XS24B.

Microphone Leads

Microphone cables are, of course, common on stage. They have a particularly difficult electrical job because of the small signals they carry and the proximity of (often noisy) mains. I am sure that almost everyone is aware of the need for balanced transmission from microphones. If you are not, don't worry, there have been elsewhere, and there will be in Sound On Stage, articles on balancing. However, it is not so widely known that professional, ie. broadcast quality, installations have always used four-core or 'starquad' cable for microphone level signal transmission. It is better balanced and, coupled with a good microphone preamplifier, this type of cable offers virtually perfect rejection of electrical interference. It's a luxury you can get used to as it's not much more expensive than ordinary twin screened. Examples are Canford SQ and SQ-R, which also has a polyurethane jacket and remains flexible at low temperatures. I would always recommend this sort of cable for on-stage microphones. If you have some or are getting some, the colour convention is to connect both red and blue to the 'in phase', ie. XLR pin 2 at each end and both white and green to antiphase, pin 3. The screen, of course, goes to pin 1.

Multicores

The essence of a neat desk-to-stage connection is the multicore, which needs to be reliable and well-terminated. Multicores for the stage employ braided or double lapped screens, or foil. Foil screening uses aluminium/mylar film, which is double-layered in better cables. Traditionally, and for heavy-duty usage, the stage-mixer multicore or snake is made from a number of individually laid, screened, and insulated cables, which are then jacketed with an overall sheath. The best known is made by Belden and used to be specified by all professional and broadcast companies; now it is available as type FSJ and FSM. The main feature of these cables is that they have heavy cores, which are therefore very robust, but the downside of the compromise is that you need to be a bodybuilder to wind them up on a drum and carry them!

For smaller and self-operated rigs, which is what a lot of readers will be interested in, a recommended cable for multicore (desk-stage) use is the HSJ Series, available up to 24 pairs. It is very flexible and uses two screens, wound in opposite directions, rather than braiding. This double 'Reussen' screen is easier to prepare for connection than a braided screen and performs just as well. Rather than go and get the biggest multicore and stage box you can find, I would suggest connecting two or three fairly small multicores, such as four or eight pair, as it is far easier to handle and carry. You then have the flexibility of taking only one or two for smaller events, and you can take the stage boxes to where they should go, such as stage front for mics, stage back for instrument amps, and to the amp rack for PA drive, etc. Larger cables don't actually work out cheaper per core. Also when disaster strikes and someone chops the cable in half, a smaller cable really is cheaper!

Speaker Cables

The whole subject of speaker cables is clouded with a strange combination of superstition and neglect. On the one side, some hi-fi devotees waste inordinate amounts of money on fabulous solid silver cables. These must be 'objects of fine art'; they certainly have no technical purpose. On the other hand, I have seen 1kW PA rigs hired out with 3 Amp mains cable for the speakers, many permanent installations connected with bell wire, and several instances of guitar leads pressed into action! There is one electrical requirement for speaker cable: low resistance (this will be covered in the next installment). This means thick heavy cable, but it doesn't have to be cooker cable! The most convenient and reasonably priced is Maplin's 79 strand cable, XR72P at 60p/metre. The only problem with this cable is that it is not circular in cross-section, which makes it a bit awkward to clamp properly with Speakon connectors. It is also difficult to coil up neatly if you are impatient. Canford HPS, at around £1.50, is a cable with the same cross-sectional area and hence the same current capacity. It is coaxial, therefore easy to terminate, and it is very flexible, so easy to coil up. The luxury speaker cable is HPS-R — this has a polyurethane jacket, which remains flexible at all temperatures and is extremely hard-wearing, but it is £2 per metre.

As for using speaker cables, don't spend heaps of money on great thick long cables, just do what real PA companies do — place the amplifiers near the speakers! In a typical small band PA, you can get very good results from a two-way active crossover system, using a normal stereo amplifier as bass and mid-high driver on each side. Then you can put the amplifier right next to the speakers and use short cables.

TENDER, LOVING, CARE

All cables are subject to physical damage. The main contributing factor to this damage is not the way they are used, but the way they are stored. Copper is quite a flexible metal, especially when finely stranded. The worst way to store a cable is one I have seen too often: twisted into a shambolic hoop, then gathered flat, with the last metre or so wound tightly round to make a sausage and the end knotted, rather like one finds new clothes lines in hardware stores. Oh dear! Lots of small radius bends and the cable sheath twisted into a spiral — this does not constitute tender loving care.

You can find the best way to store a cable by trying it out with a fairly short, three to five metre, rubber screened lead. Assuming you are right-handed (if you're left-handed, read left for right and vice versa), hold one end with your left hand, draw the lead through your right hand for a metre or so, then coil that into your left hand and repeat. The cable will usually hang flat naturally; if it has a kink, then twist the feed with your right hand until it does hang properly. When finished, the whole 'hoop' should be lying relaxed and flat. It then needs confining with a Velcro or nylon strap. Yes, it is fiddly and a pain at the end of the night. Battling with a mess of tangled and unreliable leads at the beginning of the night is also a pain. If you do find an intermittent lead, cut its plug off. This will force you to take it to a bench and repair it, rather than trying to use it again.

If you own, or are thinking of making, a multicore and stage box, please don't shove the multicore into the box with a grommet and wire it straight to the sockets. This is bound to put too much strain on the cable when wound up and stored — this is only done by bumbling amateurs. The proper way to do it is to build up the stage box with a proper multiway connector such as the EDAC. It will add about £20 to the cost of the box, but is necessary. If you are in a situation where you have heavy cables and are setting up every night, the EDAC is probably too fragile. The professional heavy-duty connector is made by Harting, uses large circular contacts, and costs a great deal, naturally. One of the joys of the sound technician who works with or plays in a band is, of course, that if you want to spend the money and do the job properly, everyone will complain about all these 'extras'; but if you don't, sooner or later it will break down. Then guess whose fault it is? If you are self-employed, of course, unreliability doesn't matter — it's only your reputation...