Friday, September 16, 2011

Cable effects

I've engaged in lengthy discussion with a friend of mine about cables this week.  To a first approximation the result is I now think various cable features such as dielectric, skin effect, resonance, stored energy, etc., can be important, and these are not always easily known as say, capacitance, which is usually specified (and which I can easily measure if it isn't specified because I have a pf capacitance meter).

High end cables such as the original Blue Heaven flatline cable may be somewhat flawed because of lack of shielding and underdamped high frequency LCR resonance in the 100Mhz region.  While you can't hear 100Mhz, it may make your equipment complain audibly.  That cable was very low capacitance, but rather high inductance, leaving me to believe it is not an interleaved cable as I had thought, but a flat cable with polarities on opposite sides.  The lack of interleaving further increases susceptibility to RF pickup, and makes for rather high inductance.  It might make a nice FM or HDTV antenna.  If that's the price for super low capacitance, I think I'll pass.  Nordost has completely changed the design in Blue Heaven II, making it a more conventional shielded design now, like all their other current interconnects, and you can guess the reasons.  But the original Blue Heaven got huge praise in the audio press.  Well, it was different.  I'm thinking of trying the Baldur XLR 0.6m interconnects I ordered by mistake; it looks reasonable.

Silver is a better conductor than copper at DC and low frequencies, but worse at higher frequencies (above about 60Hz) because it is more magnetic.  The effect of this is that less silver may be better than lots of it.  Very very thin silver plating may be better than pure copper because copper oxides are non-conductive much less than silver oxides.  My friend claims that for coax you want center conductor, if silver plated, no thicker than 30 gauge, but pure copper can be larger.  I haven't worked the details on that out in my mind yet.

Nordost cables are now using FEP for dielectric, my friend insists actual Teflon (PTFE) is still the best, with FEP and various PE formulations about comparable.  Teflon is rare in audio cables (it's not easy to make a cable with Teflon because it's not very strong) except very expensive ones, but can actually be found in various relatively inexpensive RF cables.

Belden tends to make cables with foamed PE, and their coaxes and balanced cables used for audio by Blue Jeans cable have respectable capacitance and inductance and presumably little tendency toward extreme resonance in RF because they were originally designed for video and digital audio.  They tend to use unplated copper, in stranded form for the balanced cable, and I wonder if that's actually the best.

For what little it may be worth, here's a white paper by a company that makes pure silver cables with some but not all teflon in the dielectric.

Friend suggests LL120 From Harbour Industries, but it has 21 gauge silver plated conductor, not the 30 gauge he recommends.

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