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Positive Feedback ISSUE 30
march/april 2007


We sent out the same 20 questions to 50 manufacturers, the following are their responses. The intent of the survey is to address basic questions as to design along with any questions raging on various sites, while minimizing potential chest-thumping and friendly, or unfriendly, bashing of others....

Click here to read the other interviews in the series.



Paul McGowan of PS Audio
by PFO

PFO Why do cables make a difference? Interconnects, speaker, and AC cords?

PM One of the more obvious aspects of this question is the basic nature of what we're trying to do in the first place: connect one piece to another without adding or subtracting anything.

This is a near impossible task, so the quick answer is that anything you do to the signal will have some effect on its outcome—and it won't be good. Can't be good if we're talking about passive connections as there's no way to add energy you can only lose energy.

The best we can hope to do is have as little negative effect on the signal as possible.

Let's take an extreme situation for a moment: a turntable setup. Here, we have a coil of wire and a magnetic structure (the cartridge), tethered to a high gain amplifier (perhaps 70dB to 90dB of gain) through a wire. The opportunities for error are huge. Just shielding this length of wire from magnetic fields, electrical fields etc. is quite a challenge and if great care is not taken, you'll be quite unhappy with the results.

So one extreme would be a bare wire, the other extreme a properly shielded cable. One could imagine the differences we might hear between the two extremes.

A better question might be, why would anyone think cables do not make a difference?

PFO What about metals ...copper versus silver versus gold versus what? What about blends?

PM One of the other important considerations in developing a high-performance audio, speaker or power cable, is the grade of copper to be used.

If you look at the conductor materials available, typical high purity electrical-grade copper has approximately 1500 grains (or crystals) per foot. The boundaries of all these crystals must be crossed by the signal in the process of being transmitted across the cable. It is not hard to imagine that crossing all of these boundaries must cause some sort of loss and/or distortion of the signal. This may be similar to the effects of stranded wire, and it does seem to cause the same sort of audible distortion. In video cables, this would also cause loss of information.

The next grade above normal high purity electrical-grade copper is called OFC (Oxygen-Free Copper), or sometimes Oxygen-Free High-Conductivity (OFHC) copper. This term is quite misleading, because OFC copper is not really oxygen free. It is cast and drawn in a process where oxygen content is limited, thus reducing the formation of copper oxides, which lead to a larger number of crystals. The oxygen content for OFC is typically in the range of 40 PPM (parts per million), while normal grade copper is approximately 235 PPM. The end result is that OFC has approximately 400 grains or crystals per foot, as opposed to 1500. There are significantly less boundaries for the signal to cross, and thus the signal is degraded far less. This is a substantial improvement over normal high-purity electrical wire. OFC and OFHC copper materials are not all the same, however, and these are much-abused terms. The oxygen content does vary, and it is a range, rather than a finite definition. Performance levels do vary with the quality level of the material, and not all "OFC" copper sounds or performs at the same level.

The next higher grade is an elongated grain copper sometimes called "linear-crystal" (LC-OFC), "mono-crystal", or "long-grain" copper. These coppers have been carefully drawn in a process that results in only about 70 grains or crystals per foot. Since OFC copper typically has approximately 400 grains per foot, this is clearly an improvement, and the reduced amount of crystal boundaries causes far less signal loss or distortion.

The best level of copper for audio and video applications would obviously be totally free of crystal boundaries.

Professor Atsumi Ohno began the study of the solidification of metals in the mid 1960's, and published his landmark book, Solidification; The Separation Theory and its Practical Applications, in 1984. In this book, Ohno describes his many theories and concepts regarding the processing and solidification of molten metals, and the resulting crystal structures. He goes on to describe his unique process for casting metals with virtually no crystal structure, the O.C.C. process. This concept was first conceived of in 1978, and utilizes heated molds in a continuous casting process. Eventually, international patents were granted for O.C.C. (Ohno Continuous Casting).

The copper produced by this method is small rods of O.C.C. pure copper, from which wire can be drawn and which can have Copper grains of over 700 ft in length.  A Japanese manufacturer is currently using this process and produces O.C.C. under the trade name PCOCC (Pure Copper by Ohno Continuous Casting).

From a sonic standpoint, we find PCOCC to be the best sounding materials for audio cables, although a careful blend of pure silver and PCOCC can make for an interesting and, sometimes, wonderful blend of materials.

PFO What about dielectrics... Teflon versus what?

PM Dielectrics are a necessary evil but in general, we'd like to us either PE or preferably PE foam (this is where nitrogen bubbles are injected into the PE to form a thin dielectric.

Most cable designs are an amalgam of gauges, materials and dielectrics. The art of designing cables really hinges on the experience of the designer.

PFO What about measurements... what do they tell us? what do they not tell us?

PM A TDR can tell us quite a bit about how a cable can or will sound. We use TDR measurements in almost everything we design in cables.

PFO What about connectors... how important?

PM Honestly? I don't think connectors play a huge roll in cables and their performance. Certainly a crappy connector will hamper performance, but a properly designed connector vs. an exotic connector makes, IMHO minimal differences.

For example, we go to great lengths on our power cables to machine special connectors out of solid metals. The metals themselves seem to have very little effect on the performance. What DOES have an effect is the way they are connected. We machine our connectors so we can cold and hot weld them directly to the wire—that connection process is key, not so much the connector itself. The construction of the connector is key to allow us to make the proper connections which does in fact have a great deal of effect on the performance.

PFO Why this geometry... ribbon, twisted, braded, spiraled...?

PM I am going to let one of our chief cable designers, Jay Victor, comment at length on this question:

"It is well accepted among most designers of Audio cables that different gauge (diameter) wires tend to sound different. For this reason, most of the highest end cable designs use solid core conductors of varying gauges, and preferably individually insulated. It can be noted with experimentation that larger diameter conductors tend to favor, or more accurately reproduce, the lower frequencies; medium gauge conductors, the mid frequencies; and fine gauge conductors, the high frequencies. The reasons for this are not clearly agreed upon by all, but theories can be postulated, and most relate to skin effect, although theoretically, this should have no bearing within the audio range. Listening, however, seems to indicate otherwise.

Flux density is often cited, and larger conductors are said to have a higher density of magnetic flux that concentrates in the center of the conductor. This may effectively choke off the higher frequencies, and force them to the surface of the conductor. Depending on the gauge of the conductor, this will happen in varying degrees, and yield different amounts of high frequency, bass, and mid-range information, depending on how much of it has been affected by the flux density and size of the conductor. A lot of the differences in sound between different gauge conductors can probably be attributed to interactions between the different frequency ranges, probably due to magnetic effects. The resistance of a conductor also varies with gauge, and this may also play a role. Skin effect is a well known principle in cable theory, and the higher frequencies tend to travel on the outside diameter of the cable. Skin depth varies with frequency, so differing conductor diameters should have an effect on all frequencies. Depending on whether the diameter of the cable is large, or small, the surface area that the high frequencies will travel on is clearly different and the ratios of the skin depth to conductor size related to frequency will also have an effect. This should all have an impact on sound reproduction, and perceived tonal balance. The surface area of different gauge conductors also varies, and the amount of surface area in contact with the dielectric material will also affect capacitance. The capacitance will also have an impact of high frequency reproduction.

If it is established that conductor size has an influence on sound, it is not hard to imagine that the shape and design of the conductors might also play a role. It has been established that flat, or rectangular conductors, do have extremely beneficial sonic characteristics. This may be related to the surface area of these conductors, and it may also be related to the fact that based on skin effect theory, bass signals tend to migrate to the center of a cable. Since a flat or rectangular conductor has no magnetic center like a round conductor, this may tend to prevent the concentration of low frequencies, and give a different sonic response. It also appears that flat conductors, as in round wire, do tend to have some frequency relationships related to size. In listening tests, it appears that flat conductors tend to reproduce the midrange particularly well."

PFO What about cryoing? What is going on with this?

PM We cryo treat our fuses, and this seems to have a beneficial improvement to the sound. I have, on several occasions, sent our audio and power cables to be cryo treated and honestly couldn‘t tell one from the other.

PFO Why shielding? Why not shielding?

PM You have to shield. One of the precepts of any good cable design is to make sure you keep out what wasn't there in the first place. Shielding has its downsides: too much of it will restrict the sound, but unshielded cables (while sounding more open) just don't cut it in my opinion.

PFO What about run-in? Why is/isn't it important?

PM Run in? It really works, I've never heard it not work and while I've heard dozens of theories on the subject, most of them sound like voodoo or BS. I do not know the real reasons. What I do know is they need burn in.

PFO What about lengths? Why are/aren't they important?

PM They are important. Remembering that cables can only damage the sound, never enhance it, then it stands to reason the longer the cable the worse the performance. Technically, the longer the cable the more roll off you get due to higher capacitance—but in many cables, this may well be beyond anything we can hear, even if you take into account phase relationships (that also change with capacitance). But more than rolling off the highs, or screwing up the phase, one of the worst things you can do to a preamp, for instance, is place a long interconnect on its output. Especially a tube device. Why? Because you're loading down the preamp's output stage. Try an experiment to prove it to yourself. Use a short interconnect to tie your amp/preamp together. While listening, add a 10 foot or longer interconnect onto a parallel set of outputs on the preamp. The soundstage collapses almost immediately. It's an easy test,.

PFO How did you get into cables or audio or both?

PM Well, they're sort of hand-in-hand but I got into this some 35 years ago as a music lover and neophyte design engineer. I had never even heard of an "Audiophile" but I was involved with broadcasting and music and my friend Stan Warren really got me involved in the high end side of things.

PFO What is your fundamental design philosophy/goal?

PM To do no harm. Cables shouldn't enhance or detract. Rather they should be as neutral and "not there" as humanely possible. I think that's one of the reasons I work so hard at sourcing different geometries, different materials, different philosophies of design: it's all an effort to wring the most of what's there out into the open.

PFO How do you approach accomplishing those philosophies/goals?

PM First from a philosophical point of view, then from an engineering perspective, finally from a listening and voicing perspective.

I first decide what I am trying to accomplish (make the BEST cable I know how, or perhaps make the best AFFORDABLE cable I know how, etc.). Then, philosophically, how might one go about accomplishing this task.

Once decided what the "spirit" of the project is and how it could be achieved, I then start the engineering, looking at materials and geometries that will fill the bill. We built prototype cables and then the listening begins.

Listening, testing and voicing: if I change this what happens to the sound? Once I learn this about a cable, I proceed to try and manipulate the design with extremes – if this makes a fuller sound, how far can I go with it and what else am I losing…etc. It's a lot of work.

PFO How successful do you feel you have been at achieving the goals that you have set for yourself?

PM In power cables, extremely successful. I have compared our designs with just about everyone's and we win hands down. I think we've got the world by the tail when it comes to power cables.

Audio cables, we have really good ones but frankly there are a few better. Like Walter's NBS cables, they're nuts to build but they sure sound great!

PFO How do you plan to push beyond what you have already accomplished?

PM I can't discuss that right now, but we have something in the works that you may see in another year that's simply stunning.

PFO Where is this all heading?

PM I haven't a clue. I am not much with the crystal ball actually.

PFO Others that you admire?

PM Walter Fields of NBS, Bill Lowe of AudioQuest, and Ray Kimber of Kimber Kable.

Click here to read the other interviews in the series.