The PS Audio Power Plant P300 is simply a source of fresh AC power for your audio or video components. Think of it as a stereo amplifier that can only output one frequency at one AC RMS voltage. The P300 converts the AC from your wall outlet to DC, just like every amplifier. The positive and negative DC power-supply rails power the gain stages, just like every amplifier. There is an on-board sine-wave oscillator that feeds the input of the amplifier with any frequency from 50Hz to 120Hz in 5Hz steps. The P300 generates balanced AC power, which differs from the power most people have in their homes on the 120VAC circuits. Each of the P300's outputs has 60VAC on it, but they are phase shifted. This produces the full 120VAC that your components need to operate. Balanced power has the advantage of canceling a worthwhile amount of noise on the power line.

This kind of power-line product is called an AC regenerator because it converts AC to DC then generates new AC to feed to your components. The regeneration process removes harmonic distortion and DC offset from the power line. No ordinary PLC can do this no matter how much it costs. In addition, you effectively remove almost all the noise from the AC power line. You get a squeaky-clean 60Hz AC sine wave out of the P300. This new sine wave looks impressively perfect on an oscilloscope, but power analyzers and spectrum analyzers tell an even more detailed story about just how clean this AC power is, even if the AC feeding it is far from wonderful. There are limits though. Amplifiers of any kind are not perfect devices, but the fact that the P300 uses a solid-state amplifier to generate the output AC waveform ensures very low levels of harmonic distortion.

Operation

The P300's front panel has a dual-mode LED display. One mode shows the output frequency from 50Hz to 120Hz. The other mode shows the power output of the P300 from 0 watts to 300 watts. This display helps you to stay under the 200-watt-continuous operating level. There is a green LED in the display when power levels are 200 watts or lower. Exceed 200 watts and a yellow caution LED comes on. A push-button on the front panel switches display modes. Another push-button cycles the output AC frequency from 50Hz to 120Hz in 5Hz increments. The last push-button puts the P300 in standby mode with no output voltage but with internal circuits still on.

The P300's back panel has four orange hospital-grade outlets, a fuse holder, an IEC connector for the power cord, a ground post, and the "real" power switch, which completely turns off the P300. Also included is a surge suppressor for a 75-ohm cable from an antenna, dish or cable TV. Unfortunately, there is no internal shielding over the RF signal path inside the P300, and this connection may or may not be a significant source of internally radiated RF. But either way, it just seems logical to shield any possible RF source from the inside. Elimination of RF from the AC power is one of the reasons for employing a power-line conditioner in the first place, so it just seems counter-intuitive to have an internal RF-radiation source, even if the RF doesn’t impinge on any critical internals of the P300. If this concerns you, it is an easy thing to avoid -- just don’t connect your 75-ohm video cable to the P300.

One thing to note: PS Audio chose a confusing term, "power factor," to use for the name of AC power-line frequency. Defaulting to 60Hz for North America, you can manually select 50Hz, 55Hz, 60Hz, 65Hz, etc. -- all the way up to 120Hz. Instead of calling this "AC line frequency," which it really is, PS Audio chose to call it "power factor" instead. There is an actual term "power factor" that is related to the load efficiency and correcting loads to use AC power more efficiently. People who know what a power factor is may be confused by PS Audio’s terminology, but less knowledgeable owners will never notice the malapropism. By the time you read this, PS Audio may have reverted to the correct terminology; a recent press release indicated that they would drop the use of power factor in order to eliminate confusion.

The sweet, the sublime

What has made people so enthusiastic about the Power Plant P300 is the audio sound quality it helps produce. The P300 does more to improve the sound quality of source components than any power-line conditioner I’ve used. In fact, in the last 15 months I’ve evaluated 18 AC-power-related products from eight different manufacturers. None of them, even in combination, could do as much for sound quality as the P300. The improvements are most obvious in terms of smoothness and transparency. String sound, for example, is revealed to be considerably smoother than you ever before have heard from your system. It’s as if an extra layer of fuzz around the tone of each note is removed. Hearing string tone without that fuzz is very exciting the first time. The honeymoon period lasts a long time as you go back to re-listen to all your old favorites. And this doesn't apply only to bowed instruments. You hear it with piano, guitar, dulcimer, autoharp -- anything with strings.

Focus on woodwinds and there is a similar effect. Reed sound is purer and better defined. The body of the instrument takes on bell-like clarity. Brass instruments are similarly enhanced. The bite remains fully intact, but the tone is purer. Cymbals shimmer better and have a real-life sound to the mixture of percussion and ringing. Drums are hardest to hear any tonality improvement in, but subtle detail emerges from snare and kick drum that reveals them to be a better representation of the real thing. The raspy sound of the snare is more intact, and the kick drum has that solid, round tone you hear from the real thing. Tympani do show a tonality improvement, and I found that pitch differences from one tympani to another almost seem magnified.

In addition, the P300 does the "background silence" thing better than more traditional PLCs. This reveals subtle detail that was previously masked by noise. The goal of being able to forget the equipment and get lost in the music comes a step or two closer.

Line-frequency adjustment

No review of the P300 would be complete without mention of what happens to the sound when you use AC line frequencies lower or higher than the standard North American 60Hz. There is no technical reason that most audio components won’t operate just fine at frequencies other than 60Hz as long as the line voltage remains constant at 120 VAC. There can be exceptions, and P300 owners should check with manufacturers before changing the line frequency supplied to their components.

This review was written after an extended exposure to the P300, and since my earliest observations, I have reviewed, re-thought and re-tested what I heard when changing the AC line frequency. This re-evaluation caused me to alter my initial impressions. It is now apparent to me that lower AC line frequencies produce bass with full power at the actual lowest frequencies that are being reproduced. In other words, you get the most bass power at the lowest fundamental frequencies when you select 50Hz. While making this re-evaluation, the P300 powered my reference tube preamp and CD/DVD players and/or DACs. To hear what’s really going on in the bass requires main speakers or subwoofers capable of flat-to-20Hz performance. It was easy to be fooled when the main speakers started pooping out at 40Hz or higher. As you increase the AC line frequency above 50Hz, there are increases in impact at higher frequencies. If your main speakers do not go much below 40Hz, you might think that setting the P300 to 60Hz or 80Hz actually provided better deep-bass power, but it does not. Furthermore, as you get above 90Hz or so, you can think you are hearing improved bass impact when, in reality, you are hearing more impact in the mids and lower mids, which, when overlaying bass frequencies, can make the bass sound like it has more impact. Deep bass alone has no impact per se; it is rather soft-sounding. Just listen to a subwoofer with the main speakers disabled to hear what I mean. Bass impact really is a function of higher frequencies, mids and lower mids usually. With the P300, I found that higher AC line frequencies improved the presentation of higher audio frequencies, while lower AC line frequencies improved the power of bass delivered at the lowest audio frequencies.

If you don’t have a system that is flat to 20Hz, you can experiment with the AC line frequency to give you a little extra fill-in bump right where your speakers might need it the most. It is difficult to predict exactly where this improvement might be most useful due to differences in speakers, rooms and music being listened to. So each P300 owner should take the time to step through the various increments. Pick the one that sounds like the best overall match, and try to avoid concentrating only on highs or mids of bass when doing this as all three will be affected. You’ll need wide range music to make this evaluation. It may take some familiarization at each setting to get to the bottom of what’s happening in your system.

Feet and power cords? Of course!

Many audiophiles have discovered that they can get some interesting changes and sometimes even improvements in the sound of amplifiers by selecting certain feet and certain power cords to use with those amplifiers. What is the P300? It’s an amplifier. Just because it outputs AC voltage all day and night doesn’t mean it’s immune to the same kinds of changes you hear in normal audio amplifiers when you change feet and power cords. Of all the feet I tried, I ended up preferring Nordost Pulsar Points (aluminum) the most. The sound became more assured, firm and clear, more decisive if you will. The power cord that produced a noticeably better sound compared to all the others was the JPS Labs Power AC, an eight-gauge power cord designed specifically for amplifiers.

The bitter after the sweet

The rave opinions on the P300 tend to omit its drawbacks, and there are a few of them to consider. First, the P300 is large. It is not very wide, 8", but it’s deeper than many racks, 20.5" deep and 4.5" high. This makes it difficult to deal with from a shape-and-space point of view. And if you pull a fair amount of power from it, say 150 to 200 watts, it runs pretty warm, perhaps 110 to 115 degrees Fahrenheit. The entire chassis is the heat sink, so circulating air is required around the sides, top and bottom. You may not be able to place the P300 in a rack unless the shelves are quite deep and widely spaced. Even the front panel gets quite warm when you pull close to 200 watts continuously. So the size, shape and heat generated may banish it from the rack, but you shouldn’t place it on carpet either. The bottom of the chassis needs air too. Besides the cooling issue, the P300 sounds bad sitting on carpet.

Another consideration: The P300 really isn’t all that powerful, and you can’t run a whole lot of equipment with it. It might run eight DVD players, but who needs that?. A tube preamp with four tubes will draw 100 watts or so. A 27" direct-view video monitor will pull 100 to 200 watts, with 32" and larger tubes usually needing even more power than that. The P300 is rated for 300 watts peak, 200 watts or less continuous. The headroom is for momentary loads that go away after a short time. Most video monitors suck a huge amount of current on initial startup before settling down to a relatively steady load. In fact, the draw from a monitor power-on is so severe, the P300 can actually experience a rather severe voltage sag momentarily. These can sometimes be enough to turn off a DVD player or preamp that might be connected to the same P300.

The last bit information has to do with the operational stability of the P300. I experienced some problems using the P300 with a Toshiba 27" monitor. Something about the load this monitor presented to the P300 caused the P300 to go into "thermal runaway," which resulted in the review unit becoming physically very hot to the touch -- far hotter than it would run with a 200-watt load. This heat could even be present with the TV off, because as with most TVs these days, off is not really off; it is more like nearly off. Some power is used to keep the tube partially warmed and to hold your various settings in memory over long periods of inactivity. I was never able to use the TV with the P300 for more than a day or two before the thermal runaway would be encountered. PS Audio has no immediate explanation, but the output of the P300 does not like to see capacitance. You should not use after-market power cords with parallel capacitance, nor should you use most conventional PLCs on the output of the P300 due to most of them having parallel capacitance. The thermal-runaway condition did not affect the output voltage; the P300 continued to supply 120VAC at 60Hz (or whatever frequency you set it to). This was a frustrating situation since the P300 improved video-image quality of the monitor considerably more than any other power conditioning device I’ve tried.

So on the one hand you get this great improvement in image quality, but on the other hand, whenever this monitor is connected, the P300 runs hot enough that your fingers can take only one or two seconds before you are compelled to remove your hand. This is a sign that the load the monitor presents is not appropriate for the P300. The heat, however, seems to not have bothered the P300; it continues to offer its particular brand of magic with various audio source components. As long as I don’t connect the video monitor, I have no overheating problems. After experiencing problems with the Toshiba monitor, I tried an older Sony 25" XBR and a 27" Samsung monitor and both produced the thermal-runaway problem. Perhaps something was going on with this particular review sample, but I suspect that the P300’s aversion to capacitance on the outputs has something to do with the problems I encountered with video monitors. Fortunately, the P300 did not become permanently damaged as a result of the condition.

It remains to be seen whether the Power Plant P600 ($1995) will give video fanatics having large direct-view sets or moderate-size rear-projection sets a boost in image quality without the thermal-runaway problems.

Conclusion

The PS Audio P300 is unique among under-$1000 power-line products as it actually generates fresh AC power for source components. It is essentially a stereo amplifier with a 60Hz oscillator on the input and four AC outlets instead of binding posts. Used within the modest load limitation of about 200 watts continuous, the P300 can make a significant improvement in the sound quality of any appropriate component plugged into it -- preamp, DVD player, DAC, transport, turntable, CD player, surround-sound processor, whatever. In addition, the P300 provides the best video-image quality of any power filtering or enhancement product I’ve encountered to date -- with some potential thermal-runaway problems from video monitors. Audio perfectionists will appreciate the removal of a previously unnoticed haze from every sound, something not done by more traditional PLCs. Video enthusiasts will appreciate the deeper, more dimensional images. The $995 cost is not cheap, but it is fair given the degree of improvement the P300 offers.

...Doug Blackburn
db@soundstage.com

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