Cable Troubleshooter

Here are some interesting hints for trouble shooting audio, wiring and cable problems from our good friends at ProCo Sound.



A CHAIN IS ONLY AS STRONG AS ITS WEAKEST LINK.
ProCo began building cables when we were still building P.A. systems in the mid-70s. We found that most of the reliability problems experienced by our clients were due to inadequate or badly made "off the shelf" cables, rather than major component (i.e.: AMPS, MIXERS, SPEAKERS, ETC.)failures. The LIFELINES process was developed and our system reliability problems vanished.Of course, we now build hundreds of thousands of cables a year. With that many going out, we do get a few back (less than 1/2 of one percent)! Probably half of those returned , however, have nothing at all wrong with them other than looking their age. To help our customers keep their equipment in A-1 operating condition, we are offering this brief collection of tips for troubleshooting cable-related problems in sound systems.

INSTRUMENT CABLES
The first thing to do is to be sure the jacks in the equipment are in good shape!This is very important -- you can replace cables forever without finding a "good"one if the jack in your guitar is loose. Likewise, be sure that the controls and switches are not noisy or intermittent. These parts do wear out eventually; often a crackle that seems to be a bad cable is in actuality a good cable in a worn out jack.

Most problems occur within the first foot of cable at each end. This can be isolated by supporting the plug (holding it tightly in the jack) while flexing the cable behind the plug. Bending the cable at different angles will often reveal broken solder connections or wires. If the plug itself seems noisy when wiggled in the jack (assuming the jack isn’t worn) it may have a chipped or missing insulator ring between the tip and sleeve, or a loose tip contact inside.

The cable itself is best checked by going along it in a "hand-over-hand" motion, gently tugging every few feet. Sometimes a broken center conductor works fine until the cable is stretched slightly and the broken wire ends are pulled apart. Likewise, a broken shield that may work "at rest" generally makes a lot of crackling noise as the cable is tested in this way. Finally, keep in mind that "bad cable noises" -- crackling, intermittent hum and buzz, signal cutting in and out -- can also be made by foot pedal effects with bad jacks, switches, battery snaps or AC adaptor plugs, or by microphonic preamp tubes (12ax7, etc.) A cable that works but hums loudly may be a speaker cable in disguise -- be sure the cable is shielded if it goes between instrument and amplifier.

MICROPHONE CABLES
"XLR"-type connectors are physically much more rugged than phone plugs, but they can still have bent pins, worn female contacts or crushed shells. Most reliability problems start with loose or missing screws for the shell ground or cable clamps. These should be checked periodically and tightened as needed. General testing guidelines are similar to those for phone plugs, but there are some different booby-traps to avoid.

For instance, many "bad" hi-Z mic cables (XLR to phone plug) are simply wired with the wrong pin "hot" for your equipment. Sometimes it’s pin #2 and sometimes it’s pin #3. The only way to avoid trouble is to check the spec sheet or the owners manual for your equipment when in doubt. This kind of problem can also crop up with any equipment that has 3-pin XLR connectors carrying unbalanced signals. ALWAYS MAKE SURE THE PROBLEM IS WITH THE CABLE AND NOT THE WIRING OF THE EQUIPMENT!

Another problem to watch for, especially in complex systems, is that of ground loops -- hum and buzz can be caused by having the shield connected at both ends of a balanced line. Other ground problems can occur with direct boxes and mic splitters. Some cable manufacturers (NOT ProCo) ground the shells of XLR connectors (tie them to pin #1), which can totally defeat ground lift switches.Finally, make sure the connectors in the microphone are tight -- just like a bad guitar jack, you can change cables all night and it will still hum and crackle!

SPEAKER CABLES
Make sure that the cable is unshielded and of at least 18 gauge wire. Shielded cables are not good for speaker hookup because they can’t carry the current demands of a loudspeaker. They can also cause problems because of their capacitance, which can result in amplifier instability or breakdown. Be especially careful of phone plugs on speaker cables -- check for loose tips, broken insulators, etc. As before, the basic testing process is the same as that for instrument cables.

TAKING CARE OF YOUR CABLES
Good cables cost money and like any piece of gear should be treated with a certain amount of care for best performance and maximum life. Whenever possible, try to run cables so they aren’t stretched tightly, or being walked on all night. Taping them in place helps keep the stage neat and averts a slew of potential disasters.

Cables should be coiled loosely in 12 to 18 inch loops. They should NOT be wound tightly around the elbow! "Elbow Action" results in a lot of unnecessary strain on the cables and also makes them much harder to uncoil and lay out flat. A loose coil helps eliminate kinks and becomes a very fast procedure with a little bit of practice. a very loose know can be used to secure the coils, or cable ties can be easily made from short lengths of cotton clothesline. Not to mention, that these days many manufacturers are sending out their cables with Velcro cable ties already on them so they don’t get lost.

Using these simple guidelines can help you avoid untimely equipment failures and greatly extend the life of your cables. After all, cables have a tough enough job - why make it any harder for them?

Posted with Permission from ProCo Sound (www.procosound.com)