Drubin wrote:
If shorter were better, than no cord at all would be best. Why not just continue the Romex out from the wall and hardwire it into the component? (Has anyone tried this?) This would be the equivalent of no power cord since the PC's function is simply to handle that last six feet anyway.
I'm afraid that it is not equivalent. That last six feet of power cord can have 1/5 to 1/10 the inductance of the ROMEX in the wall. Therefore, if you run 36 feet of ROMEX directly to the component, and you compare this to 30 feet of ROMEX and a 6-foot low-inductance cord, then this is like 30 feet of ROMEX compared to 36 feet of ROMEX. The full-ROMEX solution will have higher inductance. Shorter is better. you can read more about inductance and its effect on a power feed on my website: http://www.empiricalaudio.com
This is because these cords are not merely supplying the last six feet but are also doing *something* to the power--filtering or whatever--to improve what gets to our components. If this is the case, it could be reasonable to conclude that longer might in fact be better because it will provide more of that whatever-it-is it's doing.
No, longer is still not better. There are two scientifically verifiable effects that power cords can have:
1) lowering inductance of the entire power feed
2) filtering the ground noise
The second one has to do with ground-loops. IF your system is completely wired using balanced IC's, then this is a "dont-care". However, most systems are single-ended, and therefore prone to noise from ground-loops. Filtering on the ground lead of a power-cord can reduce or eliminate some of this noise, particularly at high-frequencies. The other thing to understand is that this ground-loop noise is not continuous. It is sometimes related to the signals in the wires itself, causing crosstalk between left and right channels for instance. This is because the ground-loop noise is realted to the voltage drops in the ground-return paths of the interconnects. Single-ended systems are a knarley problem at best...