Why do AC cords make so much difference?

Hdm, I wouldn't know as have not had a ground in over twenty years....The ground in my house only extends as far as kitchen, baths and laundry....

The info that Mr Crump presented about iron core transformers vs toroidals is pretty well known to anyone that has ever measured various aspects of transformer performance. Bob and i are basically on the same page in this regard and on several other AC related "beliefs". As such, you now know several of the reasons why i have preached the superiority of "old school" Iron Core ( E-I ) transformers in the past. They are quieter ( blacker background ) due to increased AC filtration and they ( typically ) offer better dynamics / bass performance due to reduced core saturation. I don't know anyone that doesn't want equipment with a lower noise floor and increased dynamic range.

I mentioned something similar to what Bob brought up earlier today prior to seeing these comments. You can follow along on the thread entitled Best Cable Tweak Ever. I'm trying to find a source on the web to support some of the info that i posted and as soon as i can, i'll forward a link to it in that thread or cut and past the info that i find. Sean

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.