The EM Poll

Knowledge and Power

Oct 1, 2005 12:00 PM, By Eddie Ciletti

           

No matter what size studio you have, power-related noise can cause serious problems. The typical scenario in the personal studio goes something like this: the console is on one side of the room, and the keyboard and rack modules are on the other side. The system, however, always has power-related noise, sometimes even with the mixer faders down.

Power-related noises with analog gear are obvious and fairly easy to troubleshoot, because you can hear changes instantly as you experiment. Hums and buzzes in the analog domain may be the only clue to mysterious problems in your digital devices; power-related noises may not be audible but they can affect equipment performance.

When I used to make house calls for a living, I was usually able to pinpoint and resolve such issues. Even if I offered advice over the phone, it was never quite enough and my presence was requested anyway. Perhaps my explanation was too matter-of-fact, or the client never believed that they had the power to fix many of the problems. But you do have that power. In this article, I will address a number of power-related topics, from chasing down and minimizing a variety of noise problems to determining your power capacity and optimizing distribution.

If you choose to take the DIY approach, have respect for electricity: wear socks and shoes, don't stand in a puddle of water while working, and always keep one hand in a pocket while probing (with a meter, for example). Basically, you don't want the jolt to hit you across the chest, from hand to hand or from hand to foot. If the electrical investigation requires you to go beyond your comfort level, find a knowledgeable electrician who is sensitive to the needs of a multimedia system.

Tree, Trunk, and Limbs

Randomly plugging your gear into the most convenient outlets around a room can be the beginning of trouble. Power distribution in a home or office is not configured to audio standards, so there is an increased potential for noise when using more than one outlet.

FIG. 1: With the Tree, Trunk, and Limbs method, imagine that the outlet is the tree trunk and the outlet strips that are plugged into it are the branches.

The first questions that I ask a customer is how many outlets are in the room, and how many are being used? I suggest that everything be plugged into one outlet using the Tree, Trunk, and Limbs (TTL) approach to power distribution (see Fig. 1). Think of the outlet as the bottom of a tree trunk. Plug an outlet strip into the trunk and connect the branches (more outlet strips). Then plug your gear into the branches.

Typically, when I visit a customer's studio, I notice that at least two outlets are being used. When asked why, the customer usually explains that he or she didn't think one extra outlet would make a difference and that it's inconvenient to use only one outlet.

Although it may not be an ideal solution — it does have limitations — the Tree, Trunk, and Limbs method distributes the same power and ground to all your outlet strips and gear, which is the ultimate goal no matter what size system you have. If you have noise problems, that approach will most likely reduce or eliminate most of them.

Noise Noise Everywhere

Every electronic product you own dumps noise back into the power line. Power-related noises can be distributed by the power wiring or through the air by induction. The best receiver is the electric guitar, which acts as a divining rod for radiated electrical noises. That's because a single-coil guitar pickup and a power transformer — such as those found in amps, power supplies, and wall warts — have something in common: they are coils of wire wrapped around a hunk of iron. A transformer radiates an electrical field, and a single-coil guitar pickup does just as its name suggests.

A humbucking pickup has two coils, one of which is wired out of phase with the other. Any noise that is common to the coils and in phase is rejected. That type of phase cancellation technique is a common strategy for dealing with noisy lines.

Computer and video monitors also have coils, which coerce electrons into creating recognizable images on screen. Flat-panel displays have coils to generate voltage for the light source behind the panel. Both technologies radiate noise, so you should gather your audio harnesses with cable ties and dress them as far away from power sources as possible.

Light dimmers and fluorescent lights also generate electromagnetic interference (EMI). Bill Whitlock, president of Jensen Transformers, recommends using an AM radio to track down noise sources, such as defective transformers in fluorescent light fixtures. To do this, tune the radio to an unused frequency and walk close to any potential noise sources: the radio will pick up and amplify the interference.