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In the Forum: Audio Discussions
In the Thread: It’s mad, mad, mad... electricity.

Post Subject: Line (grid) Power, waveform symmetry and THDPosted by floobydust on: 2/20/2009

Power from the company grid is usually pretty decent in most respects, or at least it used to be. In the last 25 years or so the average home has seen an increasing number of devices which have switching power supplies (computers, monitors, etc.) which are anything but a uniform load on the AC power. The amount of "dirt" that these devices can create (noise, distortion, RF, etc.) on the line can get pretty bad. Worse yet, many convenient end-user devices impose modulated RF on the power line for communications, which includes low-bandwidth networking, non-wired intercoms and more. The point being, that the average home and it's diverse devices probably contribute more distortion to the power line than anything coming in from the grid. Multiply this by all of the houses fed from the grid and various distortion components become significant.

The PP2000 is nothing new in concept. 30 years ago we referred to such a device as a "True" UPS, as there was no switchover but an AC to DC supply which kept a bank of batteries topped up which in turn fed a DC to AC inverter which powered the equipment (generally large computer systems). One specification that is not listed in any of the (PP2000) documentation is the THD rating. Audio equipment still uses THD as a measurement to declare a known operating parameter. It would seem only logical that the amount of distortion of the sine-wave power driving the equipment would have some effect if it gets too high. How high it too high? I doubt anyone has done much research on this and I'm certain it would vary quite a bit between different pieces of equipment.

There are other devices out there that provide line regulation and low THD as well. There are CVS transformers (Sola and others make these), fancy servo-controlled variac based units and of course high-quality sine-wave inverters which are common in remote battery and solar power systems available today. All of these devices are designed to supplement and/or replace grid systems and THD is a measured and published specification. Most of the larger systems are rated at less than 5% and some of the better (albeit smaller) units publish typical THD values of 1.5% to 2.0% as a maximum.

Before I would invest in a PP2000, I would perform some measurements on the grid power to see how bad it really is. I would be inclined to put a more robust and usable power system in with commercial gear and run a few extra dedicated and shielded lines for the audio gear. In the event of a larger power losss (somehow common in South Florida) it would certainly be more useful and the accuracy of the sinewave power would be well known. I could also listen to music when the rest of the neighborhood is dark... and make an espresso as well.

Regards, KM

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