Why do AC cords make so much difference?

Here is my explanation - and the theory behind my cable designs:

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.

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 (my older cord) 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.

Thanks, Audioengr. Can anyone add to BWhite's initial comments on a parallel thread re resonance-damping?... i.e.,
use of fillers to isolate/absorb/quench electro-mechanical stuff (60 or 120Hz?...higher?) thought to be functional here.
Furutech yells about non-magnetic materials, and even grounds the steel clamp-screws in their IEC, while a cable manufacturer or two fills their stuff with steel grit or even magnets (!), and obviously totally opposite approach!
I'm experimenting with high-density NON-ferrous dampers as a moderate-cost methodology to address these purported nasties. Could I be just creating a low-pass filter rather than further cleaning up the noise-floor?? Thanks for the input. Ern

Depends on the dampers and their position with respect to the conductors. In general, adding parallel (shunt) capacitance is not a problem, but adding series inductance is. If you had an LCR meter this would tell you whether you are degrading it or not. As long as the fillers are non-ferrous you can be relatively sure they will not increase inductance.

I'm going to start marketing some power cords very soon and decided to share the design here with you folks.

First of all, you start off with heavy ( 8, 10 or 12 gauge ) bare copper wire. You then take all three conductors and twist them together as tightly as possible. Select one wire as the hot, one as the neutral and one as the ground and wire them into the AC plug and IEC jack accordingly. I will GUARANTEE that this design will allow a greater amount of current flow in less amount of time than any commercially available UL approved design on the market. The initial amount of energy that is drawn upon first use of this cord will amaze you. I guarantee that the results will be so drastic that you would swear it was like the first "bang" for those of you that believe in the "BIG bang" theory. On top of that, you will not believe just how quiet your system is and how much the noise floor has been lowered. You would swear that your equipment was not even turned on it is so quiet. Your "black background" will be SO black that it resembles charcoal. I GUARANTEE IT !!! Sean
>

PS... The above is all a hoax. Do not follow these directions unless you want to burn down your house : )

Audioengr,
I love your calculations and I think your intentions are good, but unfortunately -

1) Capacitor banks in power supplies are designed to handle transients at peak power levels. At normal listening levels only a fraction of that capacity is used. I agree that peak transients at full volume might distort due to voltage sag on the power rails, but I would be more worried about hearing loss than distortion in this case.

2) The AC power in the U.S is 60HZ, not 20KHz. (Duh...) If you are worried about a 20KHz component getting into the signal path through the power cord, then you would want a power cord with higher capacitance to filter it out. Any amplifier that doesn't have adequate bypass and isolation in the power supply shouldn't be in your system in the first place... so any power cord that results in an audible improvement would be a band-aid rather than a fix to the root cause of the problem.

To be fair, I should say that there are probably homes out there with enormous amounts of noise on the AC power. While replacing the power cords to all of your equipment could conceivably make a difference, the proper remedy would be to install a power filter/conditioner.