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The wires and patch cables you use with your system are the glue that holds your system together. Smarter people than you and I working for manufacturers have designed and built audio equipment that, when properly and appropriately connected, will deliver peak performance. The one part of the equation that you have complete control over is the interconnection of this gear.

There are times when a piece of equipment is going to fail. I've had brand new amplifiers out of the box not work; but normally if no sound is coming out ... you've got a bad connection(s) somewhere.

I should define the term "bad connection." I do not necessarily mean a cable with connectors on it that has a broken or shorted contact. Nor do I only mean a break in a conductor somewhere. These are easy to test for and repair or replace. Good soldering etiquette, proper handling, and attention to strain relief will minimize these types of problems.

The most frustrating types of bad connections that foul up the performance of a system are ones when there appears to be nothing wrong with the cable!

You have an output from a mixer that is a male XLR. Although it is line level out, and uses this type of 3 pin non-shorting connector, the mixer's manufacturer has wired the output unbalanced. To facilitate this, Pin 1 (ground) has been strapped with a wire jumper to Pin 2. Pin 3 of the XLR is your positive side of the signal. This is called Pin 3 hot.

Now lets say you have an equalizer that you want to put after the console output. This also has an XLR connector on its line level input. However, for some reason, the manufacturer designed and built the Eq with an unbalanced input, and they configured their wiring as Pin 2 hot. Thus they have a jumper strap between Pin 1 and Pin 3. This time Pin 2 has the positive side of the signal.

Initially, you would say you're going to have a phasing problem, but the reality is worse. The minute you take a perfectly good male to female XLR patch cord and connect the console's output to the Eq's input you get nothing!? You check the console without the Eq; you check the Eq without the console; you even meter the cable. Everything works until you combine them. Why?

The answer is not as obvious as it is frustrating. You have dead shorted the input of the Eq. All three Pins of the XLR have been connected together. Think about it. Pin 1 and Pin 2 are jumped together on the mixer. Pin 1 and Pin 3 are jumped together on the Eq. When you plugged the patch cable into both units, Pin 1, Pin 2, and Pin 3 are all shorted together .... Result: The Eq's input will shut down and not pass any signal.

This is just one example of "inappropriate" connectivity. Manufacturers don't help the situation. Many don't publish in their Owner's Manual the complete details of their products. Others have weird special case situations. Two situations come to mind:

1. The standard (or as they now refer to it) Classic Mackie 1604 mixer with all those TRS (Tip, Ring, Sleeve) ¼" jacks on the back has a very strange quirk. The Main Left and Right outputs are wired out of phase to the rest of the console! This means the ring, not the tip of a ¼" TRS plug (also referred to as a "stereo" plug), is what will receive the positive side of the audio signal. The tip is the negative. Mackie says if you read the fine print of the manual, this is explained. I bought both of my 1604 consoles used with no manuals. We found it the hard way.
2. The Crown Macrotech series amplifiers have a potentially costly condition that is less than obvious. The amps come stock with the "P.I.P.-FX" input card in them. This card has the TRS ¼" jacks and XLR input connectors on it. You can use the ¼" jack with either a balanced signal coming from a TRS ¼" plug, or an unbalanced signal by using a TS (Tip, Sleeve - also referred to as "Mono") ¼" plug. If you buy the amps with a "P.I.P.-CLP" input card, you cannot feed the ¼" inputs with a mono plug (unbalanced). This connection creates a condition in the amp which will lead to burnt up speakers. I know a person that this happened to. Crown puts no warning on the face of the card, but says you have to read the fine print of the manual.

A few manufacturers' publish documents that help you make or choose the correct patch cables. Yamaha's Owners Manual is hard to read (too many things lost in the translation) but full of diagrams and How To's. Rane includes an excellent wiring chart with all new products. EV has the P.A. Bible Series available.

My last suggestion is to talk to the people that repair this equipment. They will tell you what you did wrong. Develop as good a relationship with a repair technician as you did with the Dessert Lady in the school cafeteria. You will be satisfied in both cases.