Chapter 2 – Connections
Avoiding Ground Loops
In today’s studio, where it seems every piece of equipment has complex routing and computer logic, there are many opportunities for ground loop problems to occur. These show up as hums, buzzes or sometimes radio reception and can occur if a piece of equipment “sees” two or more different paths to ground. While there are methods to virtually eliminate ground loops and stray radio frequency interference, most of the professional methods are expensive and involve installing a separate power source just for the sound system. Here are some easy helpful hints that a professional studio installer might use to keep those stray hums and buzzes to a minimum.
¿KEEP ALL ELECTRONICS OF THE SOUND SYSTEM ON THE SAME AC ELECTRICAL CIRCUIT. Most stray hums and buzzes happen as a result of different parts of the sound system being plugged into outlets of different AC circuits. If any noise generating devices such as air conditioners, refrigerators, neon lights, etc., are already plugged into one of these circuits, you then have a perfect condition for stray buzzes. Since most electronic devices of a sound system don’t require a lot of current (except for power amplifiers), it’s usually safe to run a
¡KEEP AUDIO WIRING AS FAR AWAY FROM AC WIRING AS POSSIBLE. Many hums come from audio cabling being too near AC wiring. If a hum occurs, try moving the audio wiring around to see if the hum ceases or diminishes. If it’s not possible to separate the audio and AC wiring in some instances, make sure that the audio wires don’t run parallel to any AC wire (they should only cross at right angles, if possible).
¬TO ELIMINATE HUM IF THE ABOVE HAS FAILED:
A)Disconnect the power from all outboard devices and tape machines except for the mixer and control room monitor power amp.
B)Plug in each tape machine and outboard effects device one at a time. If possible, flip the polarity of the plug of each device (turn it around in the socket) until the quietest position is found.
C)Make sure that all of the audio cables are in good working order. Cables with a detached ground wire will cause a very loud hum!!
D)Keep all cables as short as possible, especially in unbalanced circuits.
If the basic experiments don’t uncover the source of the problem, consult your dealer or technician trained in proper studio grounding techniques. In some cases, a “star grounding” scheme must be used, with the mixer at the center of the star providing the shield ground on telescoping shields, which do NOT connect to the chassis ground of other equipment in the system.
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