Problem solving for multi-component rack systems (taken from Trendz magazine Volume 4 No. 1) As you put together your "ultimate" rack set-up, the potential for problems is magnified with every component you add. There is a "best way" to do everything. Given the type and variety of your equipment and your musical requirements, the knowledge in this article will help you discover the best way to hook up and use your rack system. The majority of problems that arise in multi-component systems fall into one or more of the following categories: a) ground loop hum or buzz; b) proximity induced noise; c) gain mis-matching distortion or noise. Fortunately, these problems have specific characteristics to help you to identify and overcome them. First, let's cover the fundamentals. You should always use good quality shielded cords to hook-up all components in the signal path previous to the power amp. Use two conductor speaker cables (lower guage for longer length) between your cabinets and power amps, but no place else! Finally, you should route like cables (AC, Audio, Speaker, MIDI) together. Cable-tying AC cords together with audio cords, for example can induce enormous hum and noise. The best way to proceed with the hookup of a new rack system is to connect the basic elements (preamp, power amp and speakers) first. Then, one by one, connect the additional components (effects units, EQs, wireless systems, etc.), testing the system each step of the way. This will direct your attention to the last unit added should a problem arise. This is also the best way to trouble-shoot problems with an existing rack, when adding a new device or re-arranging things. If you have proceeded as mentioned and your rig sounds great, then stop reading and start playing! But if you've developed a problem, you have to assume it's because of the last component you added to the system. Many hum and buzz problems occur because of ground loops. The metal rack rails in your rack case tie all component chassis together creating a loop. To check for a ground loop, try moving the problem unit out of the rack, but don't disconnect it from the system. If the hum goes away, try touching a wire to the unit's chassis (unpainted surface, of course) while touching the other end to the rack rail. If the buzz comes back when the wire connects, then it's definitely a ground loop. A solution may be to insulate your problem component from the rack rail with plastic washers, plastic screws or tape. Be sure to insulate the screw threads from the unit's rack ears and leave space between other components (above or below) so that their chassis aren't touching. If you still have a noise problem, it may be due to the unit's proximity to the other components. Many processors emit some form of undesirable interference from their internal electronic components. Try moving the unit to another position, or in the worst case, out of the rack completely. A rearrangement of components placement may help although the most common top-to-bottom sequence is usually in order of signal flow. Another source of excess noise is mismatched gain. If unit "A" has its output level all the way down and unit "B" (the next in line) has its input level cranked all the way up to compensate, then a hiss problem is likely. The sending unit's output should be one half to three quarters up and the receiving unit's input should be positioned so that its led indicator (if it has one) is constantly in the "green" and occasionally in the "red." Your ears will tell you if the input is too high so as to cause clipping/distortion. You need to maintain a unified level from unit to unit for the best performance. Your last-in-line unit's output control will be the system's master volume. Of course, many of these techniques also apply to non-rackmounted systems. Proximity problems should be your first suspect, especially when wireless units are involved. You'll be surpised how much difference a few inches of space will make in cleaning up your sound! Another common problem is incorrect patching. With a rack full of wires, it's easy to make this mistake and spend hours trouble-shooting, only to find that you've plugged a "send" line into the "return" by mistake. Don't patch by "feel." Get a light in the back of your rack! Patching boo-boos don't always blow things up, set off sirens, or cause complete inoperation. So don't be fooled, suspect the obvious first! For the equipment junkies out there (you know who you are) erecting your "Rack of Doom" — beware! Systems with several components can complicate things immensely. It may be better to implement a mixer instead of a 12-step in-to-out-to-in patch chain. Your signal quality deteriorates slightly with every extra step it takes. Additionally, a MIDI thru box will eliminate MIDI delay problems associated with multiple MIDI "patch chaining." It's impossible to address every potential problem in this limited space, but a large percentage of what you'll encounter has been covered in this article. Print this page