Powerline Accessory Reviews

When I reviewed PS Audio's PerfectWave P10 Power Plant AC Regenerator,1 I found that it significantly improved the way music sounded through my system. I bought one. The main limitations I found with the P10 were its power—a maximum continuous load of 1200 volt-amps (VA, footnote 1)—and the number of AC outlets it provides: 10. When driving a 4 ohm load at even half its rated power, one PS Audio BHK 300 monoblock consumes 800W—and while 10 outlets sounds like a lot, I've run out more than once.

PS Audio's DirectStream Power Plant 20 AC regenerator (for short, they call it the P20) addresses both of those issues: It puts out more power than the P10, and it has 16 outlets. It's bigger, heavier, and looks more impressive than the P10, and has lower output impedance and better distortion figures. It also costs twice as much. PSA also claims that it sounds better—or, rather, that it makes the music sound better—a claim I investigated.

A specialized DSD-based DAC plus a high-power amplifier
The DirectStream Power Plant 20 is the biggest of three Power Plant siblings: the P20 ($9999), P15 ($7499), and P12 ($5999). According to PS Audio, the P12 replaces the old P5, producing 1200VA, which favorably compares with the P5's 1000VA. The P15 produces 1500 continuous VA—300VA more than the P10 it replaces. The new, top-of-the-line P20 puts out a continuous 2000VA and 3600VA at peak—enough to provide 70 amps of peak current—at an impressive 85% efficiency. "If our designs were only as efficient as most linear designs, they'd require far more massive heatsinks than they already have," says PS's director of marketing, Bill Leebens. It would also mean less power: 2000VA pushes the limit of what a 20-amp circuit can deliver.

Those heatsinks are massive enough as it is, contributing several pounds at least to the P20's formidable 96 lb. The rest of that weight comes from other big metal: a good-sized power transformer, gold-covered copper bus bars and other internal components, and an impressively thick faceplate with monumental handles, without which I could not have wrestled the P20 into position by myself (thank you, PS Audio).

Getting a full 2000VA out of a P20 requires a high-current (20A) circuit. The P20 has two IEC connections on the back: one fits a standard IEC C14 cable, the other an IEC C19 connector, which is standard for high-current 120V service (footnote 2). Via standard 15A service, the P20 is limited to 1200VA—same as the P12, which costs half as much, and less than the P15, which is also considerably cheaper. If you buy a P20, invest in an electrician to install a 20A circuit, if you don't already have one.

A good way to characterize the performance of an electrical source is via its output impedance, which tells you how any voltage source (including an AC power system) responds to an applied load. AC output impedance is cumulative, the sum of all the impedance sources between the plug and your electrical utility—transformers, wires straight and kinked, screw-down electrical connections, and so on.

Here's a new thing I learned while writing this review: There is no standard for AC output impedance in the US electrical code, apparently because the code emphasizes safety, not performance. Because of that, electrical systems built to code may still be "rife with impedance-related power quality problems," wrote Michael J. Russell, a consulting electrical engineer for a company called PowerLines, in a paper presented in 2000 at a conference on power quality (footnote 3).

Household electrical impedance can be all over the place, from a small fraction of an ohm to several ohms or more. It depends, for example, on how tightly electricians screw down wires in the various connections between you, the panel, and beyond. As in any electrical context, higher output impedance on an AC line means larger fluctuations in the source voltage in response to variations in the load—which is why the AC coming out of the wall is often flat on top. Linear power supplies recharge their capacitors—all of them, at the same time—near to the sinewave's peak, resulting in a sudden surge of current. That current causes the voltage to sag owing to that cumulative output impedance. Sagging voltage means that power supplies don't charge as quickly or as completely, and that their DC output is less steady. PS Audio engineer Darren Myers says that sagging voltage also means more hash feeding back into the AC line, where, if it isn't dealt with, it can feed back into other devices.

Leebens told me that the P20's output impedance is 0.049 ohm. That's about half the output impedance of the P10. Based on that factor alone, the P20 could reduce voltage sag during current spikes by a factor of 10 or so compared to what comes out of your wall. While "properly designed amplifier power supplies will somewhat reduce variations in the current supplied from the wall outlet," Myers says, "they cannot handle the massive swings often seen in urban power lines, nor can they correct distorted waveforms. Our power regenerators can, and do."

I've seen measurements that indicate that lower AC output impedance can significantly increase the current available during transients in attached devices, such as power amplifiers. Considering that the most common criticism of power conditioners—the more common, passive variety of power-treatment device—is that they can choke off current, it's not unreasonable to expect an AC regenerator to improve dynamics.

Apart from the increased power output, the main difference between PS Audio's new generation of AC synthesizers and the previous generation is in how the waveform is synthesized. Both generations begin with well-regulated DC voltage rectified from the incoming AC. A pure 60Hz waveform is synthesized in an internal DAC. The P20 then increases its power, turning it into a robust 120V 60Hz sinusoid (or whatever alternative you choose). The P20 and its siblings steal a page from the design book for PS Audio's DirectStream DAC, synthesizing a 60Hz sinusoid via pulse-density modulation (PDM), aka DSD, the calculations carried out in a field-programmable gate array (FPGA), as in the DirectStream DAC. (Previous generations of Power Plant used a standard PCM DAC chip.) The main benefit of using DSD, Leebens told me, is "more-precise and better-controlled waveforms." One result, according to PS Audio's literature, is significantly lower distortion—not only lower than previous generations, but lower than other, comparable devices.

Like previous Power Plants, the P20 can put out a pure sinewave, with adjustable amplitude, or it can alter the waveform in ways PS Audio has found to improve the sound. PSA calls such variations MultiWave. You can adjust the amount of MultiWave character from none to a lot, and you can adjust phase detection of the incoming AC waveform, which PSA says can improve distortion in really crappy power environments. An Auto Tune feature can adjust that phase automatically, and a Mode button lets you prioritize Low Distortion or High Regulation; the latter, the default mode, means fewer and smaller fluctuations in the P20's output voltage.

I tried MultiWave, and increasing the sinewave amplitude a little. The effect of those variations was small, I found, compared to the effect of the P20 in the system with its default settings. But I'm getting ahead of myself.

The US version of the P20 has 16 receptacles (six more than the P10, footnote 4), four of them optimized for High Current. The P20 is the first power-treatment device I've had in my system that's entirely adequate for reviewing: enough power for almost any audio purpose, and I can keep all of my devices plugged in and powered up—analog and digital sources, line and phono preamps, music servers, DACs, a network switch—while, for example, switching between two pairs of powered-up class-A monoblocks for comparative listening.

The P20's appearance—particularly its front handles, which are absent on the line's other models—puts me in mind of late maximalist art deco architecture. Think 30 Rockefeller Center (currently the Comcast building), but without the gold leaf. Visually, it signals power, which seems appropriate: shades of Ayn Rand's The Fountainhead. You may love the look; I think it's fine, but it doesn't matter much to me one way or the other. The P20 sat on the floor behind my equipment rack.

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Footnote 1: A volt-amp (VA) is like a watt (W), except that it doesn't account for the phase between the current and the voltage. If the load is reactive, the available power in watts will be smaller than the volt-amp rating.

Footnote 2: PS Audio has been making boutique power cords for many years, but they don't yet offer an IEC C19 cord. For now, you'll have to make do with something like Interpower's 86226020 cord ($34.02).

Footnote3: Michael J. Russell, The Impact of Mains Impedance on Power Quality," presented at Power Quality 2000 (Boston, MA: October 4, 2000).

Footnote 4: The European versions have fewer outlets because European outlets take up more space.