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.

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.

Redbeard - I suggest you measure the current in your power cords. I suspect that you will find spectral components higher than 20 kHz. Current, not Voltage ...Duh. Unless you have an expensive power supply that is designed properly in your component, this will always be the case.

Also, I recommend strongly against filtering, except on the ground lead to eliminate ground-loop currents.

I do not buy the capacitance argument. My cords add only a few hundred pF of capacitance, yet they are 10X lower inductance than the ROMEX in the wall. Until you have heard a really low inductance cord for yourself, you cannot know what the improvements are.

Baloney - there is no requirement for an earth ground. There is no "shunting" of noise necessary unless the power supply is letting power line HF noise through - this is unlikely. My transport has no earth ground and it is superb.