OFC madness: Facts, not fantasy, regarding power cables for high-end audio equipment
By Howard Johnson, PhD -- EDN, March 1, 2007
| More from Howard Johnson: Check out EDN's news Tech Clips section, where you can watch short videos of Johnson presenting on technical topics such as PCB trace losses. |
Ernie, a sometime correspondent, writes: The power cord on my oscilloscope broke because we stepped on it too many times. I heard that OFC cryogenic power cables are really good but expensive (hundreds of dollars). Should I replace my cord with one of those?
Howard: In this context, OFC stands for oxygen-free copper. Such copper must smelt in a special oxygen-free atmosphere to reduce the amount of oxygen latent within the copper. Sound expensive? It is. Physicists use the stuff inside vacuum chambers to reduce oxygen outgassing.
The term “cryogenic” implies that the conductors making up the power cable have been cryogenically cooled, probably in liquid nitrogen. That process can in some cases produce large, uniform crystalline grains within the body of the conductor.
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What kind of exotic, high-tech application could possibly justify the use of such elaborate techniques for its ac power cable? Several suppliers would have you believe it is something you already own—your audio amplifier.
Ernie: You are right; it does seem to be an audio thing. I checked out some audiophile reviews on the Web, and they say that OFC cryogenic power cables can “restore the texture, dimension, and spatial cues in sound and video that EMI and RFI often obscure” and provide “deeper, blacker backgrounds and a richer tonal balance.”
Howard: Let’s look at the facts, not the fantasy.
Ordinary 60-Hz power travels miles from the nearest power station over ordinary, oxygen-rich, noncryogenically frozen wires laden with bird poop. It goes through a local distribution transformer (gobs more regular wire in there) and then travels hundreds of feet more through your house wiring to a local outlet. Do you think the last 6 ft of cryogenically altered, helically wound, hand-braided, eight-gauge wire makes any sensible difference?
You could probably solder together old, rusty coat hangers and do just as well, provided you don’t have any young children or pets in the house.
So what do you really need in a power cable? Insulation is a good idea. Stranding is good, too. Stranded wire is flexible enough to bend many times without breaking. That’s all the technology you need.
Ernie: How about shielding? A lot of high-end audio-power cables are shielded.
Howard: It’s a nice idea, but because all the other wires in the house lurking behind the dry wall remain unshielded, it doesn’t help to shield the last little 6-ft chunk.
Ernie: OK, how about silver plating? The best power cords have to be silver-plated, don’t they?
Howard: Silver plating minutely reduces skin-effect losses at high frequencies. Some RF applications use it. It has no measurable effect on small power cables at 60 Hz.
Ernie: What about EMI-noise rejection?
Howard: Your equipment, if it is worth its salt, already has a built-in power-line noise filter.
Ernie: I’ve heard that a good power cord aligns the flow of electrons into your equipment for maximum performance.
Howard: What? That whole idea is bonkers. The mean free path for electrons in copper is about 0.039 microns. Electrons are constantly slamming into something and changing direction. There is no “aligned flow.” Only superconductors can do that. The only super thing about an OFC power cable is the profit margin.
For your application, just get a heavy-duty cable with a thick jacket, and put a rubber floor mat over it.
| Author Information |
| Howard Johnson, PhD, of Signal Consulting, frequently conducts technical workshops for digital engineers at Oxford University and other sites worldwide. Visit his Web site at www.sigcon.com or e-mail him at howie03@sigcon.com. |
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I totally agree that so-called 'high-end" power cables are a waste of money! You have stated it so logically! Too bad so many people throw $$$ at those things!! Wake up, people!! It's right there in black and white!
Don Westbury - 2008-21-10 17:23:00 PDT -
To the engineers who find this ort of thing fascinating, and I'm one of them for the last 40 years, there are a large number of links about this (including the snake oil parts) on the Boston Audio Society website links page.
Certainly we would agree that gold plating "helps" as opposed to, say, a raw 6/40 solder coating... the issue is where to draw the line? Current carrying capacity? dielectric losses? wire capacitance or inductance? ...and so on. Enjoy!
Barry Ober - 2008-6-3 09:48:00 PST -
I'm hoping Pat Giacomo had his tongue firmly in cheek when he wrote his comment! If not, I'm not sure what to say, except that anyone who tries to convince me of something so contrary to common sense and engineering data had better have some hard, repeatable data to back it up. Bob Pease (of National Semi) has challenged the audio cable guys for years to come to a blind A-B "listen-off" to see what (if any) perceived difference there would be between the monster cryo/OFC/gold-plated EXPENSIVE cables and a collection of varying lengths of hookup wire when used as speaker cables. I believe he is also offering a cash prize if the cable guys can show a consistent difference. So far, no one has taken him up on it. Hmmmm... I wonder why?
Dave Telling - 2007-5-9 15:24:00 PDT -
There is just one small problem.
Power cords actually do sound different. Granted, the excuses marketing departments come up with only sound good to the lay person. And, yes, the goal is to make exorbitant profits on something as simple as wire.
Granted, wire is just wire. But my life (and job) would be a lot easier if it all sounded alike. At one time, I tried to reconcile why a cheap piece of wire could have any effect electricity travelling untold amounts of even cheaper wire.
At my age, the goal is to find an inexpensive cord that sounds decent to include with the products my company makes.
Only to have the customers say "Why didn't you put a better power cord with this? Didn''t you ever hear the.........XYZ Brand one.......?"
Just be thankful that you don't have my job..........
Pat Di Giacomo - 2007-18-7 13:52:00 PDT -
Myths proliferate in low level technical world. Thanks for your refreshing words.
There are many misconceptions about batteries, neutral (at mains), wave shape THD over SMPS, etc.
Hector Ibarra - 2007-29-4 14:16:00 PDT
