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Lightning, Colorado Springs, CO, 1988. Photo by Roy Johnson; all rights reserved.

Protect your system against ETDs

By Roy Johnson, loudspeaker designer, Green Mountain Audio, Inc.

The AC voltage at your wall outlet is dirty and noisy. All that noise is bad for your sound and your video picture. Here are the options for protecting your gear against 'Electrically-Transmitted Disorders' while making better sound.

The problem

The electric current that powers your life is contaminated by radio-frequency noise from computer and television power supplies, your CD player, wall dimmers, and fluorescent lights. It has low-frequency hums and buzzes from appliance motors and power tools. The noises originate both from inside your home and outside from everyone else served by that same AC transformer down the block or at the corner.

How many of us have looked outside during a power outage and been amazed at the number of homes that shared our same predicament? The noises are less of an issue late at night when appliances and motors are turned off. As a test, check for any difference in sound and picture quality the next time you are awake at 3 a.m.

As if low-frequency hums and buzzes were not enough, your AC voltage waveform can be distorted with the harmonics from motors and power supplies and because those are 'in phase' with the original voltage, they travel to you from all across town. A `scope plugged into the wall would show a distorted waveform. If severe enough, these will also overheat and damage your motors and power supplies.

On top of that, your AC voltage can fluctuate from low to high, depending on the time of day. When everyone wants air conditioning, the local power company may not be able to generate or purchase enough power to meet the demand, which results in a 'brownout' or complete blackout. Voltage surges occur when power is restored.

To make matters worse, you can be the unlucky recipient of voltage spikes that occur when lightning strikes power lines, power substations, your home, or your power pole out back. When the latter two weather conditions are imminent, you cannot buy enough protection. That is when you should pull all plugs from the walls.

What to do?

You can choose products to take care of the surges and moderate spikes for little cost. Filtering out some of the radio noise costs a little more. Filtering out all of the noise and/or regulating the voltage variations will cost a great deal more. Other than cost, how does one choose? Consider the following options.

Surge suppression

US$10; these surge suppressors protect against the turn-on thumps when power is restored and also modest daily spikes. Given enough of those events, though, the absorption parts inside will fail as designed, but with no indication of being disabled.

US$40 and up; this next level of surge suppressors will filter off some of the radio-frequency noise while absorbing more powerful surges and spikes. Again, they will eventually fail but at least some do have an indicator light to show they are still protecting. Compare their ratings for absorption of 'Joules of energy.' The more, the better.

Noise filtration

Reducing the noise down to much lower frequencies -- far below radio frequencies -- will improve your sound and picture. Because of the additional and expensive parts inside, these noise filters will cost anywhere from a few hundred to a few thousand US Dollars. These are specialty devices from audio manufacturers such as Audio Magic, EquiTech, Furman Sound, Marigo Audio, and Walker Audio. Each works in different ways, and may be more suitable for an amplifier than a CD player, for example. Furman Sound makes a 'Power Conditioner' with a 'Power Factor Correction' circuit that seems very interesting.

AC regulation

To regulate your home's power line to consistently operate at the correct voltage and with very low distortion (no noise) requires an 'on-line' Uninterruptable Power Supply (UPS). These are not the US$200 models that have a back-up battery, which are commonly used for computers. Those deliver your wall's power all the time, drawing only from the battery when power goes off. Because of their price, that conversion from battery power back into AC adds huge amounts of noise and distortion to the AC. Again, this is not good for sound, picture quality, or reliability. Besides, these would only run your stereo for a few minutes. They are a waste of money for audio/video use.

Low-distortion regulation is expensive. Those units operate in one of three ways.

1. Switching to a different connection on an internal transformer (an 'autoformer') as the incoming voltage varies from high or low. That autoformer may limit the current needed by your large power amplifier on dynamic swings, so expect it to work best on your video and other audio gear, or buy a larger unit. Excellent examples are Furman Sound's AC Voltage Regulators.

2. Convert the incoming AC to DC and back to pure AC. For those without a battery, see the PS Audio brand of regenerators. For those with a battery, look at the 'on-line' UPS models from Mitsubishi Electric and Toshiba. They provide a little more isolation from the incoming AC, as they are always running from the battery to provide a very low distortion AC voltage and current.

3. Convert the incoming AC to 'balanced power' via a 'center-tapped transformer' from EquiTech, Furman Sound, and Balanced Power Technologies.

All three technologies work well. We suspect the balanced power unit would work best for sound and picture.

Recommendations

Comparing all of the above, if the power did not fluctuate much at home and we wanted the very best sound and picture quality, then we would recommend looking into the expensive noise filtration units instead of the equally-expensive AC regulators/regenerators. Ask your retailer for his recommendations for your system and specific power quality issues.

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