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[Larrchild]

Still bloody expensive.
Time for "engineering samples" eh?

[bushwick]

"So why didn't you tell the world, eh?!?!"

Larr, every time I see that photo, I can hardly help myself and sometimes I just can't. Apologies.

Its fairly obvious that its one of my favorites. May this be my last outburst round here.

[Larrchild]

Funny, since that person who's name is George showed up with a dim, faulty copy of mine, I've been mulling this new one.

[mukul]

The reason for microphonic noise in a shielded cable is the friction between plastic insulation and metal shield - when the cable vibrates, it results in static.  If the plastic insulation is covered with carbon (semi-conductive) coating, there is substantial reduction in microphonic noise.  I agree with you and sympathise about problem in removing carbon coating on the end-connections.  And, it appears the cables with carbon coating are not too expensive.

I think there are certain misconceptions about Teflon in audio applications. This has perhaps to do with the fact that DuPont has given Teflon brand name to many different thermoplastics, including PTFE, FEP and PFA, all of which have very different dielectric properties.

[Larrchild]

Welcome to our discussion, Dr.Mittal!
What is the best compromise of flexibility and microphonics?
Say, for high impedance instrument cables.
Instrument, in this case, being musical!

[bruno putzeys]

mukul wrote on Thu, 10 January 2008 04:36

I think there are certain misconceptions about Teflon in audio applications. This has perhaps to do with the fact that DuPont has given Teflon brand name to many different thermoplastics, including PTFE, FEP and PFA, all of which have very different dielectric properties.

But all of them have similarly high contact charge. None of the dielectric properties of fluorinated polymers have any bearing on audio. For the time being it's still most reasonable to presume that certain sectors of the audio public simply go for the fanciest materials.

[mukul]

Thank you Larry for the welcome.

Where vibration noise is critical, the best option is to use so-called `low-noise' cables (with carbon coating on the plastic insulator).

I have done some work on interconnects for high-end audio, as well as for speaker cables, using litz construction and expanded PTFE insulation. I also read up a lot of material on various websites.  The results of my work on interconnects are somewhat preliminary, but I am informed that the performance is very good.

[Jay Kadis]

And thank you Larry for that image.  I'll never be able to look at a triode schematic again without remembering that.

[Michael Brebes]

Bruno Putzeys wrote on Tue, 08 January 2008 11:59

@mbrebes: I think I know the carbon tape you're speaking of. A carbon-loaded kapton coated with teflon which fuses with the teflon insulation of the conductors. Du Pont sells this stuff in exchange for, I believe, an arm and a leg.

The cable was horrible to work with.  We had to use thermal strippers that burned the teflon jacket.  Then cutting the stainless steel braid wasn't easy either.  The twisted pair inside had to be cut apart, then we used those green Scotch brand scouring pads to get the carbon layer off of each conductor.  Then back to the thermal strippers to strip each conductor back.  And yes, the cable was very expensive, but it was the only thing that would work to hook up an accelerometer(like a piezo pickup but with much more mass) to the amplifier.

[bushwick]

Larry, I'm pissed you didn't make it up to AES.

[Chris Ilett]

You don't come across as young OR inexperienced. You did everything right. You traced the line right to the source, and even went back and checked it.

[JGreenslade]

I'm currently looking into buying a relatively expensive stripping tool for PTFE-insulated cable at the 'mo.

Am I correct to deduce that PTFE / Silver-plated cable is the worst choice in terms of microphony? What about the firms who trumpet their usage of the cable as a selling point? It's rugged and lasts long - we know that.

Are we talking about a case-by-case scenario here? I.e. the cable will only be microphonic in very specific scenarios? And is the single-strand cable just as prone as coaxial?

I remember when I was a kid and my cartridge died, I could get a relatively strong signal just by playing the record with a strand of wire from the arm!

Thanks in advance.

BTW - I hope you wear breathing apparatus if you're using thermal strippers on PFTE insulation...


Justin

[MagnetoSound]

JGreenslade wrote on Fri, 18 January 2008 13:40

And is the single-strand cable just as prone as coaxial?

Not as prone, but yes, capacitive contamination within the insulation of single strand wires in high impedance circuits can cause microphonic effects. If you read the first half-dozen posts in this thread again, this should become clear.

Cloth-covered wires in old Fender amps are particularly prone, IME.

(You edited your post as I was typing. Sorry if this post is redundant.)

Dan

[mukul]

JGreenslade wrote on Fri, 18 January 2008 19:10

Am I correct to deduce that PTFE / Silver-plated cable is the worst choice in terms of microphony? What about the firms who trumpet their usage of the cable as a selling point? It's rugged and lasts long - we know that. Are we talking about a case-by-case scenario here? I.e. the cable will only be microphonic in very specific scenarios? And is the single-strand cable just as prone as coaxial? ... Justin

I don't agree that PTFE/Silver Plated cable is bad for microphony.  If you are concerned with microphonic noise generated by cable vibration, you need the low-noise type of cable (with carbon coating on dielectric), that's all.

By single-strand cable, do you mean plain insulated wire without braid shield and outer jacket?  That would be no good.  With coaxial construction, at least the grounding of shield can help in reducing microphonic noise somewhat.

[JGreenslade]

MagnetoSound wrote on Fri, 18 January 2008 13:48

JGreenslade wrote on Fri, 18 January 2008 13:40 And is the single-strand cable just as prone as coaxial? Not as prone, but yes, capacitive contamination within the insulation of single strand wires in high impedance circuits can cause microphonic effects. If you read the first half-dozen posts in this thread again, this should become clear. Cloth-covered wires in old Fender amps are particularly prone, IME. (You edited your post as I was typing. Sorry if this post is redundant.) Dan

It's pretty clear - thanks. I was thiking out loud a tad, and the fact that I got about an hour's kip last night hasn't improved my IQ....

I guess silver / PTFE wire should be kept for power wiring (particularly in HT valve applications), and - definitely - not used in DI circuits etc.

For signal wiring, I've been using the Van Damme twin-pair (the stuff that was supposedly developed for SSL). It's an absolute bugger to strip (almost as tricky as PTFE) and - worst of all - has a massive propensity for strip-back when even a millisecond of heat's applied... It's convenient though... Hmmm... I can always use heatshrink to disguise the strip-back...

Justin