Part 3: AC Power Conditioners

An AC power conditioner plugs into the wall outlet and provides multiple AC outlets for plugging in your audio equipment. But before we talk about what a power conditioner does, let's look at the AC power line and its relationship to an audio system.

The AC power from the wall outlet is a 60Hz, 120VRMS sinewave that powers the audio system (see Appendix B for more detail on the power line). All your components are connected via the power line. In fact, your audio components are connected to every other electrical device in your house, and to every home and factory also using the power grid.

Power equipment on the AC line generates noise that travels back into the line where it enters your audio components. The FCC regulates the amount of noise that can be put back into the power line by appliances and industrial products. This noise is called electromagnetic interference, or EMI. Light dimmers, refrigerators, and other household appliances put high-frequency junk in the AC line. Vacuum cleaners and electrical power tools are a major source of power-line noise because the fibers in the motors' brushes are continually making and breaking contact. The line is also polluted by AM radio stations; power lines act as antennae, superimposing the AM signal over the 60Hz line.

Another source of EMI is your audio system. CD players, digital processors, CD transports, and any component using a microprocessor (some preamps, for example) put noise on the power line through their line cords. This noise then gets into preamps and source components to degrade their musical performance. In addition to putting noise in the AC line, audio components with digital circuits pollute other components by radiating radio frequency noise, or RF, through the air. Digital circuits work with clock pulses and electronic switches that operate in the AM radio frequency range; their operation radiates this RF noise, which is picked up by other components.

In addition to introducing noise in the AC line through the power cord and radiating it into the air, components also transmit noise to other components through the AC ground line. The AC ground connects all the chassis of an audio system. If you've got a noisy ground on one component, you've got a noisy ground on all your components. For example, digital noise in a CD player's ground can get into your preamplifier, with the AC power line acting as a conduit for this noise. Noise can also get in the ground by leakage through electrolytic capacitors in power supplies.

All of these problems can be controlled with a well-designed AC power-line conditioner. First, nearly all conditioners filter the incoming AC line to remove the high-frequency garbage generated by factories, neighbors, and your own appliances. The filters allow the 60Hz AC to pass, but remove noise from the line. Second, some filters isolate the components from each other with small isolation transformers on some of the conditioner's AC outlets. These transformers break the physical connection between components, preventing noise from traveling from one component to another. The isolated outputs are often marked "digital" for plugging in digital components, preventing a digital processor from polluting the AC supplying the preamplifier, for example. Third, a good line conditioner will reduce the amount of noise coupled to signal ground. Finally, AC line conditioners can protect components from voltage spikes, lightning strikes, and surges in the power-supply voltage. Not all conditioners perform every function listed here; conditioners vary in their design principles, with some addressing one problem but not another.

Cleaning up the power line for source components and preamplifiers is a different job from conditioning AC power for power amplifiers. Power amplifiers have very different AC requirements and thus must be treated differently. The description earlier of what a good line conditioner should do applies to source components and preamplifiers that draw very little current. Power amplifiers, however, draw enormous amounts of current from the wall. When the power amplifier delivers a significant amount of current to the loudspeaker-for a bass-drum whack, for example-the amplifier's power-supply reservoir capacitors are drained to supply the current. The amplifier then draws a huge amount of instantaneous current from the wall outlet to replenish its filter capacitors. The amount of current pulled from the wall can be so great that the AC waveform distorts under the amplifier's current draw; the waveform's tops and bottoms are clipped off under the load. Any isolation transformer or conditioning device in the AC path could limit the amplifier's ability to draw current, and thus degrade the amplifier's performance. Power-line filters that remove high-frequency noise can benefit a power amplifier, but transformers in series with the AC supply should be avoided. These AC line conditioners that work with power amplifiers operate in parallel with the amplifier. That is, they drain noise to ground without putting any electrical components directly between the amplifier and the wall outlet.

Some audiophiles have separate, dedicated AC lines for their power amplifiers. This reduces the chance of distortion of the AC line caused by power-amplifier current draw from affecting the preamplifier and source components. Dedicated lines are often wired with "hospital grade" AC outlets. These are orange in color, and are of higher quality and are more mechanically secure than standard household outlets. Running dedicated lines to your listening room can have a dramatic sonic effect. You can also improve AC power by providing a separate, isolated ground for the listening room's AC outlets. An electrician disconnects the grounds from the listening room's AC outlets, runs a wire from the ground outside your house, then pounds a copper ground rod into the earth and attaches the wire. Your audio equipment is no longer connected to the house ground.

Because the AC line voltage varies according to the time of day and the load on the line, one may expect a line conditioner to regulate the voltage and provide a constant 120VAC to your system. Regulation, however, doesn't improve the sound of an audio system, and can actually degrade it if the input voltage moves around the threshold at which a separate transformer tap kicks in. Moreover, most high-end audio equipment is designed to work within the tolerances of the AC line supplied by the electric company. This is why power conditioners for computers that incorporate line regulation shouldn't be used for audio systems.

When choosing a line conditioner, make sure its power capability exceeds the power consumption of the components you'll be plugging into it. Also look for the UL (Underwriters Laboratories) or CSA (Canadian Standards Association) seal of approval, indicating that the power conditioner meets certain safety requirements. Choose a conditioner with a sufficient number of outlets for your present and anticipated needs. As with all accessories, try the power conditioner in your system before you buy. Expect to pay a minimum of $250 for a conditioner with just a few outlets, to several thousand dollars for a state-of-the-art system. Many excellent conditioners cost less than $500. (Fig.12-3 shows an effective yet moderately priced line of power conditioners.)

(Fig.12-3)

A new type of power-line conditioning device has recently been introduced, designed to be used in conjunction with a standard conditioner. Instead of plugging your equipment into this new device, the device merely plugs into the wall near your hi-fi system. These products act as noise filters in parallel with the AC line powering your system. In theory, any junk on the line is shunted by the filter.

A power-line conditioner can't make poor audio components sound good; instead, it merely provides the optimum AC environment for those components so that they may realize their full potentials. The sonic benefits of a good line conditioner include a "blacker" background, with less low-level grunge and noise. The music seems to emerge from a perfectly quiet and black space, rather than a grayish background. The treble often becomes sweeter, less grainy, and more extended. Sound- staging often improves, with greater transparency, tighter image focus, and a newfound soundstage depth. Midrange textures become more liquid, and the presentation has an ease and musicality not heard without the conditioner.

If you haven't tried a power-line conditioner, you may not have heard your system at its best.

For more information on Monster Power, go to monstercable.com/power/.

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