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POWERLINE ACCESSORY REVIEWS
PS Audio DirectStream Power Plant 12
Robert Deutsch | Apr 2, 2019
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In the November 2018 issue of Stereophile , Jim Austin reviewed PS Audio’s DirectStream Power Plant P20 AC regenerator ($9999). PS Audio had sent me the less expensive DirectStream Power Plant 12 ($4999), hence this review.
Why use an AC regenerator rather than plugging components straight into the wall?
Consider these two ways of powering an audio system:
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AC power is available at a precise standard voltage and frequency (in North America, these standards are 120V and 60Hz) that do not vary with time of day or load, with no distortion of the 60Hz waveform, a complete absence of electrical noise, and limited in terms of current flow only by circuit breakers and fuses. Audio equipment could then be designed and manufactured assuming the invariance of these characteristics of AC power. Such a power amplifier, say, could do its job without its owner ever being concerned about the flaws in less-than-perfect AC showing up in the amp’s output as audible distortion.
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Alternatively, while nominally 120V/60Hz, the actual AC power available varies with the time of day and the demands placed on the power supply, and its waveform may contain both noise and distortion products. It is then up to the designers of audio equipment to include in their products tolerance of deviations from the standard voltage of 120V, as well as ways to filter out AC-borne noise and distortion.
Although 1) represents an ideal that would benefit audio equipment manufacturers, as Nelson Pass said, in Jim Austin’s interview with him in the November 2018 Stereophile , “We try to build equipment that puts up with dirty AC lines.”
PS Audio’s approach (footnote 1) to the problem of dirty power lines is the Power Plant—basically, a sinewave generator combined with an audio amplifier. The Power Plants are designed to accept the power available from the wall receptacle, whatever its characteristics, and to output “clean” power at the nominal rating of the electrical supply. I reviewed the first Power Plant, the P300, in December 1999. That product was an overwhelming success, and virtually created the product category of “AC regenerator.” Since then, PS Audio has developed a range of Power Plants, with models varying in output, and refined the execution of the basic concept. I reviewed the Power Plant Premier in February 2009, and through the years, one Power Plant or another has been part of my audio system, most recently a DirectStream Power Plant 5 (footnote 2).
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The DirectStream Power Plant 12, or P12, can supply a continuous 1250W compared to the P20’s 2000W output. Jim Austin’s system includes such power-hungry amps as PS Audio’s own BHK Signature 300 monoblocks, but I thought the P12 would be an appropriate match for my more modestly powered system, which includes a McIntosh Laboratory MC275LE (75Wpc) and PS Audio’s Stellar M700 monoblocks (350W, class-D output stage), and might make for an interesting comparison with my P5. The P12 has the same form factor as the P5, but PSA says it’s a completely new design. The P5 uses a PCM-based sinewave generator; the P12’s sinewave generator is DSD-based, its design borrowed from PSA’s DirectStream DAC.
Auditioning
Pixel peeping is a term used in photography, often derogatorily, to refer to the practice of examining images in extreme detail on a computer monitor. There is no correspondingly pithy term for the audio equivalent of pixel peeping, but the practice certainly exists. I’ve been guilty of it myself, usually in A/B comparisons involving small differences. However, rather than sit in my listening chair and listen intently to how the amount of detail produced by Product A compares with that produced by Product B, I generally prefer to just listen to the music—not always sitting in my listening chair—at volume levels that vary with my mood. Then, if there’s no immediately obvious difference in what I hear with Product A vs what I hear with Product B, I move into pixel-peeper mode and start making more specific controlled comparisons.
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In this case, to calibrate my ears, I first listened to the system with the Power Plant 5 as the source of power, just playing a variety of CDs, and ending with the überfamiliar Best of Chesky Jazz and More Audiophile Tests, Volume 2 (CD, Chesky JD68). The sound was very good indeed: detailed, well balanced, with precise imaging. To beat this, the Power Plant 12 had its work cut out for it.
I then turned off all the system components and the P5, swapped power cords from P5 to P12, turned on the components and the P12, ran the P12 through its CleanWave degaussing function (as I’d done with the P5), waited 10 minutes, and put on the Chesky test CD.
No contest! As good as the system had sounded with the P5, with the P12 there was a major step forward in overall realism. With no change in volume setting, the sound was more dynamic. This was particularly noticeable with audiophile blockbuster CDs, such as Reference Recordings’ Tutti! orchestral sampler (RR-906CD), but it was also evident with more intimately recorded music, such as soprano Sylvia McNair and pianist Andrè Previn’s (with double bassist David Finck) Sure Thing: The Jerome Kern Songbook (CD, Philips 442 129-2).
In my initial bout of listening, amplification was provided by the PS Audio Stellar M700s, and as it’s likely that PSA “voiced” those amps with a Power Plant in their reference system, the P12 and M700 might be expected to act synergistically. And might it also be that amps with a class-D output stage, such as the M700, are particularly sensitive to the purity of the AC, but that this would not be the case with amps of very different design—say, my own McIntosh MC275 LE?
The improvement wrought by the P12 was, if anything, greater with the McIntosh. The midbass-to-low-bass region was clearer, with bass drums and timpani seemingly having a more solid foundation, and transients generally having crisper onsets and more rapid decays. The MC275 LE seemed to lose some of its “tubey” characteristics—it sounded more neutral, more like the real thing.
Measuring
The P12, like the P5, has an LCD screen that shows, among other things, its performance, with displays of Voltage In/Out and THD In/Out. With no music playing, the Voltage In was 129.3V—substantially higher than my house’s nominal supply of 120V—and the Voltage Out was 120.3V. The P12 was clearly doing a good job of regulating the AC voltage. THD In was 3.1%, THD Out was 0.1%—again, impressive performance. However, the P5 was nearly as impressive: 125.8V Voltage In to 119.8V Voltage Out, and 3.0% THD In to 0.21% THD Out. Given the clearly audible superiority of the P12, I expected the measured differences to be greater. What gives?
Summing Up
I asked Paul McGowan, CEO of PS Audio, to comment on the apparent similarity of the measurements. He said that the big differences were not in distortion as such, but in how the distortion would vary depending on incoming level and use. The P12 and its siblings are more resistant to influence by these factors. Perhaps even more important is the lowering of output impedance, from about 0.05 ohm in the previous generation of Power Plants to 0.008 ohm in the current models. McGowan acknowledged that the difference “might not seem like a lot, but it is a big deal,” the lower output impedance resulting in greater energy storage, peak current demand, and tighter energy regulation. “When an amplifier demands a quick burst of transient power, the straight wall socket can’t deliver it without dipping in voltage,” he explained. “And if a passive conditioner is attached, that gets even worse. But when the regenerator is there, it delivers the energy without batting an eye—and that’s where the magic happens.”
Magic, indeed!
Footnote 1: PS Audio, 4865 Sterling Drive, Boulder, CO 80301. Tel: (720) 406-8946. Web: www.psaudio.com.
Footnote 2: The P5 is a smaller version of PS Audio’s P10, which Jim Austin reviewed in July 2016.
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COMPANY INFO
PS Audio
4865 Sterling Drive
Boulder, CO 80301
(720) 406-8946
Read more at https://www.stereophile.com/content/ps-audio-directstream-power-plant-12#ugZpyzI2x3A5Thrh.99
the transformer noise moved to the P10. I have some kind of intermittent noise on my line that is apparently being filtered out by the P10. Within the house it could be a dimmer or LED lights, or it could be coming from the outside world.
