Following June's article on jack plugs, Ben Duncan here applies the same treatment to XLR connectors.

There's no doubt that XLR (or 'Cannon') plugs and sockets provide the most reliable and rugged, general purpose interconnections for audio. By the same token, they're generally more expensive and bigger than phono plugs and jack plugs, so you won't find them on equipment where cost and space have to be cut to the bone. Also in having male and female line counterparts, they're invaluable for 'the rigging' connections to mikes and one or more instruments draped across the studio. XLR leads can be plugged together for length requirements, and they'll withstand being trodden on and thrown around.

Figure 1 shows the connections for a standard XLR to XLR lead, wired pin to pin, with one-pair cable. It's mono, and can be used for all normal equipment and mike connections, whether balanced, or unbalanced.

Figure 2 shows how the chassis sockets are assumed to be wired at each end, for the three compatible, and most common, variations.

Aside from lots of standard XLR leads of varying lengths, it's handy to have a few converter leads, depicted in Figures 3, 4 and 5. These can be quite short (say 12"), so they can be easily identified. Experience also suggests that short converter leads can be easily hidden away, when out of use, otherwise they're liable to disappear. Leads which convert ¼" jack (and Bantam jack for those with professional patchbays) and phono plugs to XLRs, both male and female, are equally invaluable. This means that a jack connection from a DI box for instance can be trailed across the studio in normal XLR format, and perhaps converted to phono or jack interface at the other end, rather than hunting high and low for a suitable jack lead of sufficient length.

The Ground-Pin Examined

When XLR leads run from one piece of equipment to another, the shell of the cable plugs are grounded to the equipment metalwork via the mating chassis socket. However, this isn't true when dealing with mic connections, or when two or more low level signal leads are joined together. The upshot is that there's a gap in the shielding, where two plugs are coupled. To remedy this state of affairs, simply link the XLR's groundpin to pin 1, as illustrated in Figure 7. This procedure is particularly valuable if you suffer RF interference or the low level cables are being trailed alongside any mains wiring.

Evaluation

Figure 6 tabulates the qualities of the four line plugs and sockets, that we tested.

On the original ITT Cannon XLRs, the cable clamp remains next to useless for thin cables (for example a single pair foil-screened), and the fiddly assembly screws are easily lost. In addition, the neoprene-rubber bush often rots after a while, and consequently falls off. This is very inconvenient, as spares are not readily available.

On the plus side, the neoprene-rubber insert, in the female variety, withstands a lot of abuse, and the latching action is always good (something many females seem to have in common?) I didn't review the AXR series, introduced in 1983, as the improvements appear to be mostly cosmetic, although the price is lower.

On the Switchcraft QG Series, the steel body, though tough, rusts once the nickel finish is worn, or scratched. The insert plastic resists soldering irons, but goes brittle with use and sometimes cracks (something they appear to have in common with roadies). Difficulties have also arisen with the cable-clamp screws if thin diameter cable is used, as the screw vanishes inside the body if contact pressure is not established before the thread runs out. Additionally, in the past year, tolerances on these have lacked their accustomed precision. In fact, it's high time that Switchcraft invested in some new machine tools and revamped this design, now over 18 years old. Otherwise, these plugs have the best ground contact and a reliable latching mechanism.

The original Neutrik NC series XLRs have better clamping and strain relief than the Cannon or Switchcraft models that they sought to compete with, but the terminals are too small for many screen wires, not to mention chunky speaker leads; the soft plastic insert melts (unless you're extremely dextrous with the soldering iron), and the latch action is frequently abysmal, particularly when mated with Switchcraft or Cannon sockets. On the plus side, these XLRs are readily available with gold plated pins, which can help make long term connections reliable and crackle free.

Pending other developments, Neutrik's new X Series XLRs seem set to become the industry standard. They're available at lower prices than any of the opposition and manage to retain and even improve on the original Neutrik's advantages without introducing any hidden snags. Being the most compact and lightweight of all XLRs, they're available with gold plated pins, have the best cable-clamping and strain-relief system (regardless of cable diameter), and have managed to omit finicky screws altogether. Meanwhile, the terminal size and latching are almost up to the standard set by the Switchcraft QG series, and they also feature a usefully 'snazzy' option whereby one can fit different coloured bushes for cable identification, which is very useful in the average studio jungle.

Conclusion

For once, there seems to be little doubt about what to buy if you're in need of XLR leads. Whether you require only one lead or are wiring a complete installation, the Neutrik X Series are the current 'flavour of the month', being logical, well executed and visually identifiable.