Ask Eddie: From the Ground Up

Oct 1, 2011 9:00 AM, By Eddie Ciletti



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With no wiring diagram in hand, I had to start with the tried-and-true: The ideal is a “star” ground system. That’s one simple sentence for man, one complex novel for mankind! Copper rods (roots) are inserted into the earth; the power company does this, but to ensure a long-term clean connection for audio purposes, sometimes multiple rods are used (and must be periodically maintained). From this literal earth connection, a large-diameter cable feeds a bus bar (tree trunk), to which are connected individual but still significant cables (branches) reaching out to each “audio rack,” within which is another bus bar feeding individual ground wires to each piece of gear in the rack (leaves).

The purpose of a dedicated zero-volts distribution system (ZVDS) is to be substantial enough to maintain low impedance between the “central star” and each piece of equipment, no matter how far away. Impedance is the AC version of DC resistance. Because our power distribution system is AC, all of the potential differences—from chassis to chassis—will be some combination of the 60Hz fundamental, plus various related harmonics (buzzes). The ZVDS will be so much more substantial than the safety ground as to literally be the path of least resistance. It is also the most cost-effective.

To the best of my detective abilities, I learned that the client’s only ground-distribution scheme was exclusively through the isolated-ground “hospital-grade” power outlets of the orange variety. This is a good start, but remember that the power outlet ground is for safety, not for low noise. Conventional 120VAC power distribution is unbalanced: The wide blade of the plug is neutral (tied to ground), and only the narrow blade is actually hot. The round pin is safety ground so you won’t get electrocuted while shaving in the shower.

The client had two rack0mounted balanced power boxes. BP uses 120-volt transformers with a center tap tied to ground so that 60 volts appears on each blade—120V from blade to blade. I have never been convinced that BP is “The Big Solution,” primarily because, due to cost, it tends to be used “selectively” rather than system-wide. There are other reasons.

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