@j
4. Highly triboelectric polymer insulation can cause unwanted signals when mechanically stressed (e.g., vibration), especially in high impedance circuits, from shield and inner conductor reptation.
@ed, I routinely tap capacitors when choosing them. As I've said before, name brand mass production polyprops (e.g., Wima, Panasonic) give little to no response. The worst I've seen are "audiophile" caps with Teflon or paper dielectrics.
4. Highly triboelectric polymer insulation can cause unwanted signals when mechanically stressed (e.g., vibration), especially in high impedance circuits, from shield and inner conductor reptation.
@ed, I routinely tap capacitors when choosing them. As I've said before, name brand mass production polyprops (e.g., Wima, Panasonic) give little to no response. The worst I've seen are "audiophile" caps with Teflon or paper dielectrics.
For whatever reason cables can be pretty microphonic. I may have mentioned this elsewhere but coaxes can make great burglar alarms strung through fences. It may be mostly the piezo properties of the dielectrics or the triboelectric effects inside the cable. I had wondered about the impact of moving a center conductor inside a shield affecting the capacitance since it would seem to have very little effect.
Perhaps "Audiophile" parts are the ones that have the most pleasing reverb tail from acoustic excitement. Caps, cables, mechanical construction, turntables (very few people seem to advocate acoustic isolation of turntables ??) are all sensitive to vibration. Cable hangers will help increase the acoustic susceptibility of cables. Most systems I see are set up as shrines between two speakers ensuring a thorough acoustic bath from the reproduced sound. Maybe Pioneer was on the right track 30 years ago. Pioneer SR-202 Reverberation Amplifier - Hi-Fi Database - Other
What seems to happen is that the layers of the cable move inside of each other as the cable is flexed. The usual fix is a conductive rubber layer between the insulator and the shield.
Exactly. This causes rubbing as the shield and insulator (or center conductor and insulator) rub across one another. Conductive rubber is not an audiophile-approved insulation, but this effect can be minimized by using a low triboelectric insulator or giving the insulator a tiny amount of conductivity by adding a little antistat. Not useful for ultrahigh impedance circuitry, but for general audio use, easy to do.
At approximately what level of source impedance (assuming the usual high load impedance) would these capacitive cable effects become a problem? It seems to me that any voltage generated in the cable is going to have a very high Thevenin impedance so easy to short out. Is this just another one of those issues which is only audible if you use sources with unusually high output impedances?
Keithly makes ultra-low noise triax, but it's for use up to 10^15 Ohms at BOTH ends.
jn is right BTW tribo is from charge retained by contact or friction.
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I ran into it with some Teflon cable driven from 600R and terminated with 1M.
watch out for fakes
One must also be concerned that the PRC producing the carbon from confiscated Tibetian temple ware or even worse fake copies. The use of recycled blowup doll for the latex has been found to be sexier to some ears.
John (N)
SY stole my thunder about tribo electricity. I test with a 10K load and it shows up with no DC bias. With DC I get much higher levels of noise.
Please note audio interconnects are to my view poor quality coax. The shields are often just spiral copper wires. Then there is the frequency range of interest. I do not expect uniform field distribution due to the gaps or grouping of the shield conductors.
I suspect bending of the inner conductor through the spiral shield can occur at tight bends. That should really mess up higher frequency use.
I am not planning on publishing any of this as it is so cable dependent and the ability of so many to graft their own viewpoints on it would create too much heat.
I have just been curious as to why there are different forms of distortion in some of the cables I play with.
I don't think there is anything really new here, just looking at what is often ignored.
ES
P.S. I noted you said the change in C is very very low. -40db would meet that for some so we may actually not have any disagreement in our own observations!
SY stole my thunder about tribo electricity. I test with a 10K load and it shows up with no DC bias. With DC I get much higher levels of noise.
Please note audio interconnects are to my view poor quality coax. The shields are often just spiral copper wires. Then there is the frequency range of interest. I do not expect uniform field distribution due to the gaps or grouping of the shield conductors.
I suspect bending of the inner conductor through the spiral shield can occur at tight bends. That should really mess up higher frequency use.
I am not planning on publishing any of this as it is so cable dependent and the ability of so many to graft their own viewpoints on it would create too much heat.
I have just been curious as to why there are different forms of distortion in some of the cables I play with.
I don't think there is anything really new here, just looking at what is often ignored.
ES
P.S. I noted you said the change in C is very very low. -40db would meet that for some so we may actually not have any disagreement in our own observations!
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Two comments:SY said:
- I am surprised that this can be seen at 600R; was this an unusually long cable so high capacitance? The capacitive reactance of the cable is effectively the source impedance of any internally generated audio voltages.
- Given this, why are some people so keen to use Teflon insulated cables? Do they prefer this effect i.e. it avoids 'cold, sterile' sound?
Which is consistent with a compressive capacitance change
It is a very serious issue for coaxial cables, bending... I'm responsible for installing a bit over 2000 coax cables running 500 mhz signals into lots of cable tray and conduit, and I had to give a small presentation to the muscle doing the install, about 20 kids. The times micro 240 all the way up to the 1/2 inch heliax all have minimum radius specifications, and if I bend it more than that, the shield will ellipse on me, the core will be off center, and the cable will start to have magnetic field outside the shield. That increases the cable inductance, increases it's characteristic impedance, and drops it's propagation velocity. Since we are sensitive to about 60 picosecond time of flight deviations between 4 cables at a time, I had to read them the "cable bending radius riot act". edit: I almost forgot...Overbending opens the loop area of the cable, and the electronics reading those coax cables will interpret ground loop intrusion and coupling from power cables (535's, 262, 4/0) as an error in the system reading, and will attempt to correct. A bad cable will mess up the entire machine.. Since I would be called in to troubleshoot at 2 in the morning, I would not be a happy camper.
For audio, overbending the cable will cause local inductance deviation, and that means coupling to magfield as a result of local geometric loop area.
That is unfortunate. The testing and results are worthwhile, as well as suspicions as to what cause and effect are. As long as conclusions are prefaced with the statement that they are theorized.
Agreed. The question of piezo or tribo in the dielectric vs faraday's law and earth's field are interesting however.
j
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I've never really explored why this happened- cable length was not excessive. I just vowed never to use that (promising looking, Teflon and silver) cable again. So many interesting problems, so little time to explore them! I still have some lengths of the offending cable in case anyone else wants to play with it.
I would suspect (though no proof) that my experience was exceptional and that most other Teflon cables could be fine. Other than fashion, it's unclear to me why that would be preferred for audio- perhaps the superior properties for timing circuits?
No, I got this cable before there was an Internet.
Maybe 1980? My observation was ca. 1985. It was leftovers after building a piece of lab equipment (this was for a detector for a T-Jump experiment) which found its way into my apartment rather than the dumpster.- Status
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