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Sound Advice

Star Grounds, Loop Areas, & Electrical Safety In Project Studios, Edit Suites, & Other Compact Audio Installations Part IV by Neil A. Muncy

Surge Suppressors are widely advertised as the answer to noise and interference problems in all kinds of systems. Consider a few points. First, as mentioned in previous issues, conventional Metal Oxide Varistors (MOV) surge suppressors incorporated into power bars are in widespread use. Unfortunately, unless they are built to a robust standard, which many of the older ones weren’t, they may constitute a serious fire hazard, because when MOVs fail, they often get hot enough to melt the plastic housing of a typical power bar long before the fuse or circuit breaker operates. (Murphy at work!) Newer ones must meet a considerable more demanding UL/CSA specification, and are supposedly safer.

Let’s suppose the computer(s) in your installation are fed by a power bar with a built-in MOV. When a surge comes along, the “bad stuff” is diverted into the equipment ground conductor and supposedly finds its way back to the service entrance. If the equipment ground path is more than a few feet in length, the natural inductance of the equipment ground conductor will be enough to significantly limit the flow of high-frequency noise current, which is what transients and surges are made of in the first place. Instead of getting rid of surge energy, what happens is that for the duration of the event the entire computer systems’ ground reference voltage goes up towards the level of the surge itself, which can be hundreds of volts – if not more.

If the computer is sitting there all by itself and is not connected to any other equipment, this problem may be more academic than real. But if the computer is connected to something else, and the rest of the studio equipment is either not on a MOV surge suppressor fed by the same power circuit, which feeds the computer, or worse yet, is fed by a different power circuit altogether, during a surge there can be sufficiently high voltages between the computer’s “protected” ground reference and an “unprotected” studio equipment ground reference to cause major noise and even permanent damage.

If you are absolutely convinced that you need MOV surge suppression, the best way to minimize this problem is to first configure your studio power as described above, and then use the same kind of MOV suppressor on each power circuit feeding the room. Connect all of them to the central hub of your power distribution system, and then run all branch circuits from there. A much better solution is a new Series Mode surge suppressor technology, which does not contaminate equipment grounds. A bit more expensive than good MOVs, but much safer and much more effective in the long run. You can find out about it at www.surgex.com.

Getting rid of noise in audio systems is nothing more than applied Good Engineering Practice (GEP), the formula for which is: BP + GOCHS = GEP (Basic Physics + Good Old Common Horse Sense). The proponents of alternative esoteric grounding schemes would do well to keep in mind that Mother Nature wrote the original script for the show – and she don’t do re-writes!

Neil Muncy has been around since the days when recorded sound was analog mono and vacuum tubes ruled the audio landscape. He has been a consultant in the audio field for many years, and can be contacted by e-mail at: nmuncy@allstream.net.

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