Minimizing noise in audio circuits is a well-known subject pioneered by the innovators of telecommunications: the phone companies. More basic even than negative feedback was the idea that audio could be sent over a pair of wires, where the signal on one was 180 degrees out of phase with respect to the other. As is well known by now, this “balanced” approach allows any noise or interference induced onto the two wires to be cancelled at the receiving end. A similar technique called balanced power can offer improvements to the quality of power delivered to audio equipment, and the results can positively impact the low-level noise capabilities of a system. Balanced power is found in some of the leading mastering and recording facilities where noise floors must be at the absolute minimum.
Balanced power can be produced in a nearly identical manner to balanced audio, where a transformer accepts an input and produces two signals, 180 degrees out of phase and a center tap, which becomes the common or ground. In practice with AC power in the United States, this creates 60 V from one side to the center tap, and phase inverted 60 V from the other side to center tap. From side to side, the total is 120 V, but very importantly, the grounded center tap is clean thanks to common mode cancellation. Obviously, the same would hold true in other countries with higher voltages, the point being that the power is split or balanced around a center common point. Note that the National Electrical Code in the United States recognizes balanced power, although many electricians might not be familiar with it. If you are ever looking at power from an outlet and see the strange sight of 60 V between each side and ground, have no fear, it could be balanced power.
There are products from several manufacturers that accomplish this 60-0-60 (or 115-0-115 for Europe) balanced power output, and one source for additional information can be found online at http://www.equitech.com/faq/faq.html.
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