What are 6 feet going to do for me?

Ozfly wrote:

1) Would larger/more capacitors negate the need for a low inductance cord (i.e., is there a substitution effect?)

To some extent, this is true, although there are effects from the inductance of the traces and wires in the power supply as well that are not improved by adding more caps. There is also the added inductance due to the size of these caps and the surface area that they consume on the circuit-board etc... Adding more caps does not necessarily improve the transient response either, since caps, particularly large ones, tend to have large internal resistance. Adding smaller low "ESR" caps can sometimes be more effective and they consume very little space. Power supplies that respond well to high-power transients at all frequencies usually have a mix of different cap sizes and types.

2) Are shorter cords better than longer cords since the inductance would decrease?

Absolutely. Like all cables in audio, shorter is always better, unless of course you are using the cable as a tone control, whihc I do not recommend.

Warrenh wrote:

Since you say that cheaper cords have higher inductance than the more expensive ones: Is it possible to find a $200 cord with the same inductance as one for $1000?

I suppose it is possible. Generally, the things that cause inductance to be low tend to make the cord big, inflexible and more expensive due to more individual wires inside. It is more likely that you will find a cord with less profit built-in that is low-inductance.

Is there a way to know what the exact inductance rating, if there is such a thing,is?

Absolutely. This can be measured with an LCR meter at several frequencies. I like to use 20kHz. All my cords and cables have published measurements. Unfortunately, I am the only manufacturer that I am aware of that publishes power cord characteristics. I believe the reason is that most vendors do not really understand why their cables work or modify the character of the sound. They also are probably suspicious of inductance being the primary factor. They amay be afraid that if they were to publish their inductance numbers, their cables would not rate well. Many of them feel that cords should do some level of filtering. I have found this to be detrimental myself. There are probably situations, particularly with line-level components where filtering the line current could make an improvement, but I believe that the vast majority of these can be attributed to common-mode noise from ground-loops in the systems. Filtering the power-cord is a band-aid at best and does not get at the root-cause of the problem, which is the ground-loop.

If so, is there, then, any other reason to get the $1,000 over the $200 one given identical inductance stats? OR, do we just assume the inductance level is low because they are expensive?

There may be reasons, such as lower dielectric absorption. The use of Teflon insulation in one cord and PVC insulation in another cord with the same inductance can make a difference in the transient response, because their dielectric absorption willl be different. This is a more difficult parameter to measure, and its effects are more subtle. I would be willing to bet that you would notice the difference, though. It gets down to splitting hairs at this point. And, you cannot expect the inductance to be low just because the cost is high. Many cables are sold at prices that people are willing to pay, due to hype, advertising, reputation etc... has nothing to do with performance.

And, how low is low? Do we get to a point of inaudible differences?

Low would be <.05uH/foot. As far as point of diminishing returns, I believe this depends on your amplifier power supply. If it is really poorly designed, you will probably hear improvements for every notch you go lower all the way to .00001 uH/foot. Also depends on how much ROMEX there is in the wall, after all the last 6 feet of a 25 foot run behaves much different than the last 6 feet of an 8 foot run. For all practical purposes, <.01uH/foot is impractical and probably could not be built without using superconductors or really wide copper strips, like a Goertz cable.

Audioengr, you say that "like all cables in audio, shorter is always better." I speak with no engineering authority, but I want to suggest that this may not be true with power cords.

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 think our collective experience would predict that hardwiring in this way would not be better, at least not better that what some of the great PCs do for our systems. 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.

As someone once put it to me: If you like what your power cord does to the sound of your system, why wouldn't you want more of that?

Warren,

From my experience I'd say that this is all incrimental. I'm using a Stealth too and yes things do get better again when you upgrade the cable that is feeding it. I would not say that the improvement is as dramatic as when I first installed my Stealth, but it's there. The question is how much money do you want to spend. It seems that there is no end to this power stuff. Don't go crazy with spending tons of money. I upgrade and play with things a little at a time when my cash flow permits.

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...