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Old 1st November 2008, 08:22 PM   #10101
PMA is offline PMA  Europe
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Iron? Or metal dissimilarity junction?
 
Old 1st November 2008, 10:03 PM   #10102
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Actually I am more interested in talking about even more subtle properties of specific materials, first.
 
Old 2nd November 2008, 12:03 AM   #10103
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Before I discuss metal purity and its implications, I might again point out that two separate areas of cable optimization are possible. There is material purity and quality, and the other is geometric configurations. Geometric configurations have been around since the late '70's and started with Litz wire twin pairs or by special winding configurations to change the arrival time between the high and low frequencies (Bruce Brisson).
For example, Mendota Research used Litz wire as the primary and return connector, put clear Teflon tubing around each conductor, then put both Teflon covered Litz wire leads in a copper shield, and attached quality connectors to each end. This allowed that the shield be completely separate from the ground return wire. We tried these for a few years, and sent samples to Harry Pearson at 'The Absolute Sound'. The best recommendation that I got was that Harry wanted more, if possible, for his audio system. That is a true recommendation, as he had so many other choices at the time. If anything, these cables sounded better, if slightly 'tizzy'. Still they were my choice for many years.
The other geometry used a dual spiral winding on a non-magnetic former with the large wire on the inside and the small wire on the outside. While this can seem confusing, it actually becomes a 'reverse' equilizer of sorts, removing accumulated nonlinear delay. At least, I think that is the way it works. I can give some other examples, later.
In either case, skin effect is very important for the effectiveness of either geometry.
 
Old 2nd November 2008, 02:30 AM   #10104
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John,
I assume you are describing a speaker or interconnect cable, not a wire used for preamp/amp internal wiring?

Internal wire is a simple solid or stranded Teflon insulated cable. Signal and ground path are routed separately.

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Old 2nd November 2008, 03:47 AM   #10105
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I am speaking ONLY of interconnect cables at the moment, but it could be also internal wiring of amps and preamps as well, if applicable. Speaker cable is entirely separate in this case.
 
Old 2nd November 2008, 09:49 PM   #10106
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My personal opinion is that the case for skin effect and audio is highly overstated. Hawksford's study for one has been discredited by at least one person whose expertise is more suited to the problem. Mathematical results at this level of sophistication are easily misinterpreted.
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Old 2nd November 2008, 09:52 PM   #10107
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Now I would like to bring up a few points that I uncovered while looking through some books on electron flow in metals:
I had heard of different conductivity of various offerings of copper due to purity or annealing, but I had no real understanding of it at first.
Appearently it is easy to bring out these differences, that seem so subtle at room temperature, at very low temperatures. Then, different copper samples can measure quite differently from what would be expected at room temperature. It is a bit like what we do when we are measuring THD in circuits. You might say that the room temperature measurement is much like looking at a sinewave passing through a component on an oscilloscope. Unless you are clipping or have really high crossover distortion, you won't be able to tell the difference between components by just looking at the oscilloscope only. However, IF you should 'notch out' the test sine wave, and then look at the results on the oscilloscope, you will find lots of extra stuff (distortion) that is what makes components sound different. Virtually all techs and engineers when measuring THD, have looked at both the raw output signal and the 'notched signal' at the same time on a dual input oscilloscope. An FFT is another way of measurement, and is not what we are discussing here.
Well, super cooling a piece of copper or any other metal does much the same thing. Once you remove the fundamental resistance mechanism, you are left with a 'residual'. It is the 'residual' that I would like to address in future comments, and what contributes to it.
 
Old 2nd November 2008, 10:58 PM   #10108
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Quote:
Just checked, BF862 has very bad 1/f noise in reality. 80nV/rt.Hz cited at 10 Hz.
green is BF862
Attached Images
File Type: gif a-b-bf862-noise.gif (8.7 KB, 697 views)
 
Old 2nd November 2008, 11:07 PM   #10109
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Scott, you proceed this comentary. The mechanisms that cause 'skin effect' in my two examples, have nothing to do with Dr. Hawksford's work. You would do well by reading Dr. Hawksford's commentary, rather than relying on others. I have known Dr. Hawksford for about 25 years, and have had him over at my office. I was the one who contacted him when he was being blindsided by your associate, and I have read the correspondance between them. I also spoke to Dr. Hawksford after the discussion of his work had died down. He stands by his original statements, and I will give him the benefit-of-doubt, since he is a full professor, has looked at the criticism by others, and stands by his work.
 
Old 2nd November 2008, 11:11 PM   #10110
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Dimitri, an associate of mine also measured the BF862 and found it fairly quiet. He used a calibrated Quan-Tech and I trust his results, also. It may be batch dependent. That is something that I worried about, initally. The manufacturer does NOT promise or even rate low frequency noise on the spec sheet.
 

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