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SOURCE: November 2005 issue of Lighting&Sound America · POSTED: 01/05/06
How can these devices protect your gear?
It's a fact of life that AC voltage is not consistent, especially in environments where many lights and heavy-duty amplifiers are being used. Most of the time, 115V is wishful thinking instead of reality. Yet most electronic equipment used in North America is designed to operate at 115V, alternating at 50 or 60 times per second. Go too far outside of that range and you'll get problems—especially with digital equipment, which operates in a stringently regulated environment.
Power surges, voltage spikes, and electromagnetic noise can all cause potential problems with electronic equipment. There are many products available to address each area of concern, but one product group addresses all three problems. These nifty black boxes are called power conditioners or line conditioners. The correct term is power line conditioner, but, however you say it, in order to be considered a power line conditioner in the generally accepted sense of the term, the unit must incorporate surge protection, electromagnetic-interference/radio-frequency interference (EMI/RFI) noise filtering, and a certain kind of voltage regulation. For most professional installations, these devices should also be rack-mountable. Here's a look at the three issues that power line conditioners address.
At the top of the list is the line-leveling function, or voltage regulation. Most equipment can tolerate a fairly broad variance of line voltage, but each product has its limits. The voltage-regulation function of a power line conditioner establishes high- and low-voltage limits within the safe operating range of the equipment it is protecting, though today's digital gear tends to have tighter tolerances.
Ideally, the output of a power supply should be at a constant voltage. Unfortunately, this is difficult to achieve. Two factors can cause an output voltage change. As previously mentioned, the AC line voltage is not constant; the 115V reference level is just that—a reference. In fact, AC power can vary between 105-125VAC under normal conditions. The AC line voltage alone can be responsible for as much as a 20% change in the DC output voltage of a power supply. A change in the load resistance can also affect the DC output voltage. In complex electronic equipment, the load can change as circuits are switched in and out. Some regulators can maintain a steady voltage by stepping the voltage up or down. Stepping down is not a problem; stepping up lowers the available current (or amperage). That's not always wise if your equipment requires large amounts of current. For example, if you're running a conventional power amplifier at high volume and there's a sudden drop in the voltage when the amp must produce a loud or low frequency, your regulator will raise the voltage, but the amp can no longer draw the current needed to produce that note. That can cause a circuit breaker to trip, shutting down the whole rack of equipment.
Because most power supplies have a fixed internal resistance, they cannot absorb large fluctuations in AC voltage. As the load resistance decreases, the power supply's internal resistance decreases the voltage across the load. That can damage any electronic equipment; digital devices are especially susceptible to fluctuations in DC voltage.
In general, circuits are designed to operate with a particular supply voltage. When the latter changes, the circuit's operation may be adversely affected. That's where the voltage regulation function of a power line conditioner comes into play. By constantly monitoring the AC voltage level and limiting it when necessary, a more consistent voltage level is maintained, lessening the chances of damage.
Possibly the most critical function of a power line conditioner is surge protection. In addition to the constant variations on line voltage, many events and conditions can cause surges, or spikes, in the AC power line, damaging transistors, making logic chips behave erratically, and, under extreme conditions, causing transformers to explode.
Voltage spikes and surges are the silent equipment killers. You never know when they are going to occur, they happen quickly and rarely leave trace evidence (other than the damaged equipment), and they may damage one component—or all of them. Spikes might occur several times before inflicting any damage, or they could cause instant total product failure. Their ability to invade an electronic component and take out just one resistor, or change the value of just one capacitor, makes them more than dangerous. They can leave you scratching your head as to exactly why your equipment is behaving abnormally. And head-scratching in front of clients is a practice generally frowned upon and to be avoided whenever possible.
EMI/RFI noise filtration isn't a critical factor in preventing equipment failure, but it is an important step in ensuring that the best sound and picture quality are delivered on a consistent basis.
The terms EMI and RFI are often used interchangeably, though they are not the same. EMI is a specific type of noise that can be introduced into a power line, whereas RFI represents the frequency range (or pitch) of noise introduced. They often go hand-in-hand, but not always. Both can cause noise problems. Power lines can also act as antennas, picking up noise and transmitting it directly into the electronic circuitry, where it can produce an audible buzz or even cause equipment malfunctions.
EMI/RFI noise can be introduced into an audio or video signal path from many sources; the first course of action is to eliminate noise from the incoming power lines. Often, the noise comes from the equipment you're trying to protect.
In the case of power conditioners, filtering out the noise is usually accomplished with a series of passive resistors and capacitors applied to the power lines to create band-pass filters in much the same way that they are applied to a speaker system crossover to block high and low frequencies.
As more and more of the equipment people use is digitally based, the need for clean power will continue to increase. Regardless of the gear you specify into an install, some type of power protection is always a good idea. Power conditioners provide a nice combination of protection against so-called "dirty" power and noise that comes from your power source.