After Market Power Cables - Gold or Snake Oil?

Amplifiers demand current from the power-line when the capacitors in their power-supplies become momentarily discharged due to high-current transients in the music signal. This discharge condition must be quickly recharged from the power-line, through the power-supply transformer, or a voltage sag will occur. Such voltage sags can cause audible distortion at the loudspeakers. If the power-line has significant series inductance in the path from the power panel to the amplifier, this can prevent the capacitor bank from recharging in time to prevent a voltage sag from occurring at the amplifier output transistors. With a low-inductance cable, the voltage drop across the cable will be insignificant during high-current transients, minimizing the voltage sag. This allows all of the current needed by the output transistors to be supplied when they need it, resulting in fast, dynamic response to transient signals.

What is important to understand is that typical rubber cords have many times the inductance of the ROMEX in the wall, so adding a rubber power cord is like extending the ROMEX from 20 feet to 30-40 feet. Here is a calculation based on actual measurements:

A typical 6-foot 14 AWG rubber cord and 25 feet of ROMEX has inductance of 7.2 uH and resistance of 235 mohms, ignoring the plug resistance effect. Therefore, the voltage drop at 20kHz will be I*(wL+R)= I*(.905+.235) = I*(1.14). With a 6-foot Magnum2 and 25 feet of ROMEX, the inductance is 5.9 uH and the total resistance is 147 mohms. This is an 18% reduction in inductance and a 37% reduction in resistance. The voltage drop for this combination will be I(wL+R) = I(.741+.147) = I(.888). So at a fixed dynamic current I, the voltage drop in the entire power feed at 20kHz is 22% smaller with a Magnum2 power cord. I would consider 22% to be significant. The reality is even more compelling. When you add in lower plug and receptacle resistance and the fact that the di/dt on the power cord will have spectra well above 20kHz with some amplifiers, the low-inductance cord makes an even bigger difference.

Once I was reading about a modification to the crossovers in my speakers. The author explained that one of the inductors in the crossover was attached with a metal screw that changed the inductance of the circuit; and removing this screw and replacing it with a plastic one would have a great impact on sound quality. I removed the screw, and was amazed at the sound improvement. Weeks went by, and I couldn't beleave how such a small thing could make such a big difference.
Then it hit me; I had disconnected that part of the circuit months earlier, and the inductor was not even connected. So much for my highly trained golden ears!
What I learned from this exercise is that sometimes I hear improvements that are real; and sometimes I hear improvements that I expect to hear because of changes I make to my system - but they are all in my head.
As for power cords, perhaps they offer some RF/EMI filtering which is of some benefit in certain applications. Perhaps they are like the screw I removed from my crossovers. A power cord looks kind of like a snake. Perhaps there is a correlation..

Swklein, at the risk of sounding contrary, scientists do know how aspirin works. A simplified explanation can be found here http://www.howstuffworks.com/aspirin2.htm. Also, no one has ever proven that bumblebees can't fly. That notion is an urban myth and its origins are touched on here: http://www.maa.org/mathland/mathland_3_31.html.

Nonetheless, these analogies do have validity here. For example, any scientist worth his salt would observe *bumblebees* in flight and willingly argue that they CAN fly! The key is in observation of the phenomena. Whether it matches their original expectation or not should be a moot point. The same method can be applied to cables.(Note the emphasis on the pluralized versions of the subjects: one example does not make a case either for or against.)

Like most good scientists I hypothesised, then experimented and observed the results. Given that my understanding of electricity, similar to Checkmate110's, is pretty basic this test was undertaken with mild pessimism. My knowledge at the time was that, given Checkmate110's similar assumption that the wiring in the wall was equal to the cord's, upgraded power cords would not make a difference in how the system sounded. The results surprised me by proving this belief wrong. The outcome was further tested against multiple listeners with similar results. It has since been proven to be the case at multiple residences (hence completely different wiring installations). In all instances the aftermarket power cords were better than the stock ones.

Why were they better? Well, having had my original assumption disproven, I did look for basic substantiation. The aftermarket cords in my system are made with larger gauge (originally considered) and higher purity wire, use better connectors and insulating materials, are better shielded and are made with a different construction method and design. Lacking an o'scope I can't comment on their electrical properties per se, though a VOM does show them to have different resistance. In the end, the biggest reason I know they're different is because I, and others, observed their effect first hand.

Along that line, but back to the bugs again, the "proof" that bumblebees can't fly came from a physicist who initially used equations for fixed-wing craft. The product of these computations was erroneous because unlike an airplane bumblebees have moving, flexible wings. Like this scientist, my knowledge was just deep enough to allow me to make the wrong assumption initially. My believe in observation was the saving grace as it allowed me to accept the outcome even though it differed from my original premise.

Slightly off topic, but still relevant, please be aware that I am not prone toward exaggerating a product's effect on my system's overall sound. Seeing words and phrases like "transformed" and "night and day difference" used to describe a product usually leads me to believe the writer is either lacking in vocabulary or experience, overly imbued with enthusiasm, has a vested interest in promoting the product or some combination of the above. Why? Because I have not yet had an experience that warrants such a pronouncement. The best I've mustered so far is "significant" and "worthwhile investment."

That said, and to make a long story short, all of my cables, power cords included, are of the aftermarket variety. I do still question the validity of laying down "huge sums" (a quite relative phrase) for cables, but won't naysay them as I have not personally tried one I consider "outrageously expensive."

FWIW, my power cords retailed for ~$300 each. I bought them here for ~50% of that price. If you still question whether they can make a difference my suggestion would be to buy one of Subaruguru's DIY kits for $32 and give it a try. No better proof than that of the first hand variety!

I am a Building Inspector and my primary responsibility is the complete inspection of new housing. How and why PC’s work baffles me. I have asked a lot of experts and the best answer I receive is “resistance vs. load“. Another way to look at the subject is, something’s are true weather you believe them or not.

Recently I was talking with the designer/president of a prestigious cable manufacturing firm about his various AC cord offerings. Get this: even *he* doesn't completely understand why they do what they do for a sound system! No argument from me that they do work wonders; no question about that at all. Certainly the builder has his theories, but all the numbers still don't explain everything...

Case in point: based upon feature-set alone, about 18 months back I bought a fantastic famous-name $10K preamp sound-unheard. Initially I was not all that satisfied with the sonic performance, although very good, it just wasn't what I expected it to be. In fact in some respects it was less satisfactory than the $2K preamp that it replaced. Since I only change one thing at a time, after about a week allowing for some burn-in time I then decided to experiment. Shelving & footers accomplished some audible changes, but that wasn't the answer. I figured that the AC cord was fine because I had experimented extensively with different cords on the first preamp & had found a good combination. Finally I decided to change the AC cord again & I am still amazed at what happened; the new preamp completely came alive & sang just beautifully. I'm now very happy with it of course.

So use your ears & don't worry about the physics. And if you haven't done so already, burnish all of your AC cord prongs with at least an ink eraser, or better get some crocus cloth from a good hardward store & shine up those prongs bigtime. Follow with a quality contact cleaner. Your ears will thank you.