Power cord? Why?

Although this has been asked and answered many times here, I'll add to the database of discussion.

There are many reasons power cords make a difference, and "what sonic difference they make" is dependent on a myriad of design factors such as inductance, impedance, shielding, dielectric, contacts, wire type and gauge..etc etc..

Contrary to the popular refrain "why should the last 6 feet of fancy power cord make a difference at the end of two miles of Romex?" The truth is that the "last six feet" is NOT the last 6 feet from the perspective of the component, it is the FIRST six feet. In addition, EMI and other high frequency noise and interference do not travel down power lines like debris travelling down stream-- most HF noise is radiated from point sources. This radiated noise loses intensity the farther you move awat from the source, and then most of this type of noise is gone, entirely.

Now, the relevant issue becomes what are the point sources of noise that because of proximity, are potentially the most significant in effecting system performance?

Generally speaking, components in an audio visual system are all within a few feet of eachother, they are all interconnected and are tied to a common AC source (dedicated lines help). All of these components have power supplies that radiate EMI noise, and all pass noise in varying degrees back onto the power line via ground. As you approach this combination of power supplies, all of these radiating feilds of energy and noise are converging.

A system of electronis often acts as a "loop" of sorts for radiated noise and energy fields that can not possibly be (entirely) ameliorated by traditional power supplies or out-board conditioning/filtration . The type and form of AC signal isolation applied in those "first" few feet outside a component has the potential to impact the condition of the AC signal as it passes into the power supply. Of course, power supplies have their own methods of dealing with incoming noise, but most manufacturers of electronics will admit, there is no perfect way (yet) to eliminate the effects of noise riding in on the power line.

Of course, there can be exhaustive technical discussions, arguments, counter claims and the like on these forums, but the bottom line is: you HAVE to try these products for yourself within the context of your own system to judge their value and effectiveness. And because the many power cord designs on the market vary widely in terms of quality and design, you should try more than just one type or model.

There are many studios, including those owned by Phillips and Sony, and mastering engineers, recording artists, producers etc. who have found after market power cords to be a valuable tool in improving their systems and recordings. Many manufacturers of electronics/speakers in this industry use and endorse them as well. I think we've past the point where there can be any question whether there are power cord designs that can make a positive difference in system performance. The only relevant issue left is proving to yourself whether a specific product can make positive difference --in your system. Forum Q and A's all become moot at that point.

Happy listening!

Are you asking, How does a power cord affect the sound? Or are you asking, What changes in sound do audiophiles notice when they switch power cords? The answer to the first question is, they don't. The answer to the second question is, the sky's the limit.

Eldartford & Bomarc, you should consider joining the "Flat Earth Society". After all, if the earth was round, we would all slide off! And if the earth were round and also rotating, we would just be flung off into space. About the same logic here as you guys make in your posts! Or perhaps your systems are just not of the caliber to benefit from the sonic improvements of a good after market power cord. Kind of like re-jetting the carburetor on a Yugo to get better performance!

I beg to differ. Powercords do change the sound of any system. Or, am I the only one that hear a difference in every powercord I've plugged into my system? (That would be an argument for me having golden ears. However, I can't hear the difference between different isolation tweaks under my cd player.)

Here is my theory as to why they make a difference, with analysis and measurements.

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 low-inductance 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 the low-inductance 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.

And please don't give me a lot of flack about 60Hz current in power cords. The currents are very high in frequency - just measure them...