Technology Showcase: Power Conditioners
Oct 1, 2008 12:00 PM, By Bennett Liles
The wide spectrum of devices goes beyond controlling voltage fluctuations and removing noise.
The one common factor that today's various types of audio and video gear, recorders, processors, editors, mixers, monitors, and all the rest have in common is that they all require electric power to operate. On the face of it, that seems simple enough, but different types of AV gear have their own tolerance to power problems. Some can seem impervious to such things and just keep right on working, while others almost develop personalities in reaction to surges, spikes, voltage transients, and induced noise.
Today's power grid is aging, and at the same time, more devices are being connected to it that have a tendency to throw noise back into the grid. According to Furman Sound, there has been a hundred-fold increase in AC-line noise in the past 25 years. As AC power deteriorates, so does equipment performance. Devices commonly known as power conditioners or power-line conditioners primarily control voltage fluctuations and remove noise. The range in size and functions on these devices is huge, and many devices currently marketed will have other functions such as power sequencing built in as a complement to voltage regulation or power-line conditioning. Most devices in this arena provide surge protection, noise removal, and prevention of voltage fluctuations and power waveform distortion.
We've long known the benefits of using balanced audio circuits in which a third conductor is used to absorb noise-producing currents, but since 1996, that principle has been applied to power circuits as well. Rather than have one power conductor at +120V in relation to ground and one conductor at 0V, the power comes in at +60V to ground on one conductor and -60V on another, and a ground line connects to a center-tap position on the power transformer's secondary coil. This electrically puts the ground where the AC cycle crosses the zero-voltage point. Each output leg is 180 degrees out of phase with the other so that anything other than pure sine-wave AC, such as transient voltages and reactive current, sums to zero volts and is cancelled. This is referred to as common-mode rejection.
Stray noise-producing currents can come from air-conditioner, furnace, or refrigerator motors; fluorescent lighting; dimmer switches; personal computers; and radio signals being induced into power lines acting as radio antennas. The power grid was developed long ago, before many of these devices existed. It was never designed to deliver the ultra-clean power that much of today's professional AV gear needs in order to deliver crisp, color-bright video and a low noise floor for sound. This goes beyond merely eliminating rolling hum bars on video monitors and squelching hum in a PA system. Color depth and saturation can be significantly improved, while critical noise-level reduction in quiet music passages can raise dynamic range capability by 16dB or more. High-frequency electrical interference at or near the bit-stream rate can also be prevented from causing jitter in digital audio systems.
AC regeneration is the ultimate in power-line conditioning because it not only filters higher frequency noise with passive components, but it also completely renews the AC power before delivery to the outputs. The AC signal is first converted to smooth DC and then reconverted back to AC using circuitry very similar to that used in uninterruptable power supplies (UPS) for computers. The downside of AC regenerators is in increased size, heat, and of course, cost. These can run into several thousand dollars. Let's have a look at what's available in the wide spectrum of offerings in power-line conditioners.
The PowerTrip 8 from Alesis is a rackmounted unit that handles AV power needs up to a 15-amp total load. The unit contains an RFI/EMI interference filter and a high-voltage surge and transient suppressor that responds to voltage fluctuations in less than a nanosecond. The master switch controls eight rear-mounted, circuit-breaker-protected AC outlets. The unit also provides two pull-out lamp tubes and a dimmer knob to illuminate the panels of other rack gear; these lights are controlled with a separate switch. The circuit-breaker button pops out when tripped, and it is reset by simply pushing it back in. In the center of the panel is a display of the voltage level that is being delivered to the rear-panel outlets.
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