Seductive Idea
So-called “balanced power” – or more properly, “symmetrical AC power” – is another seductively appealing idea.
Explanations of the concept often mistakenly assume that the internal capacitances from power line to chassis that exist in all equipment (C1 and C2 or C3 and C4 in the figure as shown in Figure 4) are equal.
Of course, if this were true, the normal “leakage” currents in these capacitors would completely cancel because the voltages across them are equal but of opposing polarity.
But this assumption is not valid for typical real-world equipment, where one capacitance is often several times larger than the other. Therefore, real-world noise reduction is usually less than 10 dB and rarely exceeds 15 dB, a fact even promoters admit.
In audio systems, 10 dB improvements rarely “solve” noise problems. But 10 dB might be cost-effective if it makes a “hum bar” disappear from a video display. Increased cancellation of noise would require manufacturers to better match power line to chassis capacitances in their equipment, which is unlikely.
In systems where all equipment uses two-prong (ungrounded) power connections, filters and isolation transformers will have little effect on noise, but balanced power may offer some improvement. However, in systems where some or all equipment uses three-prong power connections, the effects of leakage currents pale in comparison to magnetic effects in premises wiring.
By transformer action, current flow in line and neutral wires create a magnetic field that can induce significant voltages over the length of the safety ground wire. Although this is a major source of ground voltage differences between outlets (contributing to system noise), power conditioning has no effect on it whatsoever.
Explaining Benefits
When power conditioning is installed, usual practice is to power most, if not all, system equipment with its output. The fact that all system equipment is powered from very closely spaced outlets may drastically reduce ground voltage differences between pieces of equipment.
This may explain most of the benefit usually attributed to the conditioner. But this can be done with an ordinary outlet strip or, at the very least, by powering all system equipment from the same branch circuit.
Although ground loops often involve safety ground connections, it cannot be emphasized enough that disabling them with “lifters” or ripping out the third pin is both highly dangerous and illegal. I’ve seen pricey audiophile power “accessories” whose most notable features were an internal disconnection of safety ground and, of course, lack of a UL label.
Generally, the most dramatic and cost-effective solution to system noise is to locate and eliminate the ground loops or other problems that allow noise to couple into signal paths in the first place. This approach solves the fundamental problem, which tampering with safety grounds does not.
Bill Whitlock has served as president of Jensen Transformers for more than 20 years and is recognized as one of the foremost technical writers in professional audio.