Keeping Quiet
Learn to handle hum and buzz with a critical look at system noise from the ground up
Continued from Page 3

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Small systems
Ever notice that when flying at 20,000 feet (6,100 m), you have no sensation of motion? I do not mean turbulence or steering but the actual speed at which you are traveling. To a certain extent, this analogy can be applied to ground-related noises. So long as every device is flying on the same ground (no matter how noisy), no device sees the noise. You might say that this is the ground plane. You are allowed to laugh or groan.

Here is another analogy. With one foot on a building floor and another on an elevator floor it is obvious that the elevator is not as steady as the building. This correlates to what happens when a direct box inadvertently links the system ground (via the recording console) with a bass amp plugged into a utility outlet that is not connected to the officially sanctioned ground. The point here is to translate what we already know—the sound of hum and buzz—into what actually happens when two grounds are not at the same potential or cleanliness, relative to the earth or to each other.

Tie yourself to two horses facing opposite directions and the above analogies will start to make sense. The idea is that differences between two devices puts stress on their connective as well as internal wiring. The differences come from voltage and noise variations. The problems come from gear with poor internal grounding and from wall warts placed too close to unbalanced wiring. Even a small audio system can have problems that start when multiple power strips are haphazardly plugged into different wall outlets. Distribute power from a single outlet, and chances are most of the noises will go away. This test is safe assuming that you know the system will not exceed 75% of a 20 amp breaker (15 amps) and that nothing else is on that circuit.

Connect the first two power strips to a standard wall outlet, and to those power strips, connect the other power strips in the most symmetrical way possible. You can also use a two-to-six outlet adapter that screws into a standard wall outlet; all strips then plug into that. Remove all ground-lift adapters. The emphasis here is to use a single outlet.

Power up slowly so as not to overload the breaker, and, if possible, use a current probe at the breaker box to monitor demand. The system should now be significantly quieter. If not, find all the wall warts and make sure none of the audio cables go near them. This is only a test. If the tree solves the noise problem, and the breaker is not overloaded, you have a temporary fix. Finding the problem gear is not quite as easy, but the clue is to look for plastic-insulated jacks and products with unbalanced inputs.

An awfully big build up for what seems like a rather simple but temporary solution, right? When a customer asked for this noise reduction tip, it did not help because there was one piece of gear that had to be plugged into a convenient outlet rather than follow the discipline of using a single outlet. So much for science.

Most of the noise was a combination of using unbalanced sources and cabling (MIDI modules) to a mixer that hummed with so many cables connected and faders down. Taking advantage of balanced inputs and cabling would have helped tremendously, even with unbalanced sources. The downside to affordable technology is that it makes a professional installation seem rather expensive.

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