Power cord? Why?

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...

Viridian - the point is that if you cannot measure anything, then your mind may be playing trick on you or you have not gotten to the root-cause of the sonic change. At least if there are measurements that coincide with sonic changes, then theories as to why the changes happen are more feasible. It provides some basis for explanation.

Batteries, like AC power sources have impedance. Some batteries will have lower internal impedance than others. Some will work well during transient current demands and others will not work as well to provide the transient current. There is no surprise here.

TWL wrote: "I'm currently using a large capacity lead acid automotive battery with 650 cold cranking amps, located about 24 inches from my amplifier. I have the terminals directly connected to the power input barrier strip on the amp, with 12ga OFC copper stranded wire."

24 inches of ANY wire represents a large inductive impedance. You need what is referred to as "decoupling caps", which essentially decouple the power source from the load by providing local energy storage. This means low ESR (equivalent series resistance) capacitors located as close as possible to the load. And a combination of HF caps (.01 UFd to .1 UFd) and some swamping caps (1 UFd to 100 Ufd) are needed to supply current at a broad frequency of transient currents. It would not hurt to have even a 1000Ufd close-by as well.

You may not be able to measure what you hear. Depends on the noise floor of your sampling oscilloscope. You MUST use differential probing technique for this to avoid ground-loop noise as well. This is not a trivial measurement.

You would be better off to measure the voltage drop (scope capture) across the power cord when transient music passages are being played. IF two cords have different voltages, this means that more current is getting to the amp with one than the other. If the cords didn't matter, then the currents should be identical.

"Also, the greater voltage drop in a wimpy power cord does not translate into degraded sound provided that the power supply is robust."

So, show me one amp which has a "robust" power supply. I have never run across an amp yet that did not benefit from a low-inductance power cord, except those that have inductors already in series for filtering (bad idea IMO).

Seans guidance on the power cord construction is very good. The star-quad achieves the lowest inductance. Multiples of them will be very effective.

I would be wary about using "high-temperature" wire. The copper in these is usually sub-standard for audio purposes, as is alarm, telephone and control wire. Find a good Alpha or Belden hook-up wire with pTFE insulation.

Iasi - what type of power amp do you have? Does it have an AC input filter?

Eldartford - you can buy hookup wire at: alliedelec.com

Copper quality matters, whether it's power IC's or speaker cables.

Iasi - I have had the Innersound ESL amp in my system for a couple of weeks. I know the design of this amp (by Coda Technologies) - no negative global feedback, strictly class A/B and lots of protection fuses etc.. - however, you have to be careful about removing IC's before it's fully discharged. My power cords definitely made a difference with this amp. Maybe you have not tried the right power cord yet.

Hbarrel - I will not be driving from Oregon to Akron, sorry. BTW - Power cord effectiveness has little to do with how clean the power is.... See my FAQ page at:
http://www.empiricalaudio.com

Eldartford - 99% of modern copper wire is oxygen-free. It's mostly marketing bruhaa.. There are a few examples of poor wire, but if you use a reliable source like Belden, Alpha or Carol, it's all good stuff.

Now, if you want the best-sounding wire, you should try continuous-cast copper. This is good metallurgy. you can get this at vampirewire.com.

Iasi - I understand that Roger contracted Coda Technologies to design the Innersound amp for him. Same guy that designed the Coda and Continuum amps. I have heard from one of my dealers that Roger is not a cable believer, however he does spec a low-capacitance cable for his speakers.... It is hard enough to convince believers.......

Sean - what I heard from Roger (via my dealer) is that he is concerned about the capacitance of the speaker cable resonating with the transformer windings of the speaker. I don't believe he is concerned much about the amp oscillating. I believe Roger has a treatise about this on his website.

Corona, I agree with you completely. My brother is a metallurgical engineer with 25 years experience. He has taught me a lot about this. This is why the wire needs to be fabricated properly and handled carefully in the assembly process. This is how my "Perfect Crystal" stays perfect.

S23Chang - the equivalent wire gauge is what is important, not the gauge of a single wire. Low inductance cords are always made using multiple wire to get that low inductance. Resistance is only one piece of the pie. Inductance must be low as well and larger gauge just does not get this for you.

Sean - been at HE2003, but I'm back now. Regarding Goertz, these cables make a lot of sense technically. There is no way to get lower inductance than this. Not sure why Roger would be concerned about the amps. They should be able to drive these - particularly given they do not have any global negative feedback. His concern is probably more about the speakers themselves.