RG179 (75Ω) with silver plated copper clad steel center. Teflon® insulation. Silver plated copper braid that's 95% coverage. And low capacitance for it's small diameter. Expensive from big name dealers but available on eBay for relatively cheap, especially short lengths. Sounds very good too. And lower capacitance per foot/meter then RG316 or RG174. I use it a lot.
What does it matter anyway, whether it is analogue or digital? In either case no need for silver. Given silver, teflon is a bad choice for the insulation.
For digital connections any flexible coax with the right characteristic impedance. For analogue connections any flexible coax with lowish capacitance.
For digital connections any flexible coax with the right characteristic impedance. For analogue connections any flexible coax with lowish capacitance.
Sorry, I should have made myself clear. I'm talking analogue inputs to the valve preamp
I used predominantly PTFE/silver during my years as a MIL spec wireman. It's just something I'm more comfortable using.
Unfortunately I'm limited by the steel chassis which I have to work with. Have already mounted the transformers on SRBP spacers and star pointed the ground system to minimise magnetic fields and ground loops. The sensitive valve preamp stage is picking up only a small amount of hum from the chassis now which can be eliminated by moving the unscreened existing signal input cables to the valves. My hope is that by using screened and grounded (at one end) cable I will be able to route the cables tidily without picking up hum.
Coax deals with electric and magnetic fields. Unbalanced twisted pair only deals with magnetic field; most internal connections are unbalanced.lcsaszar said:
OK. I guess they use PTFE for low flammability.BikerBod said:
Screened audio input cables should be grounded to the audio ground at the circuit input. The external input end should be grounded to the socket outer, but not to the chassis i.e. you need isolated sockets.
The analogue input signal travels along two wires.
If you use coaxial cable then the signal flow travels along the coax core and the signal return travels along the coax screen/shield.
These two wires MUST be connected at both ends, otherwise the signal route is broken.
Well, I suppose one could make a pointy-headed physics argument for static charge triobelectric effect. But that is not the important criteria. Dielectric absorption is. Teflon has the lowest dielectric constant of all materials superseded only by air or a vacuum. And I think polypropylene is a close second. It's the capacitance properties of cables that makes this important. AND, many audiophiles that use their ears agree that silver/teflon just sounds better.
I'm not in the habit of repeatedly rubbing my coax
But if you do, it still makes no difference Cu vs Ag. They're very close together in the triboelectric series so no difference there.
The thing which pointy-heads and flat-heads have in common is that they are both subject to the same laws of physics. They only differ in their understanding of this.HollowState said:
DA is of little relevance in a capacitor, and no relevance in a cable insulation. This assumes, of course, that the cable is not a few km in length and it is not driven from a very high impedance. Neither are likely in competent domestic audio.
It may just be possible that silver/teflon sounds different. The triboelectricity could introduce a small degree of cable microphony. I guess if you have paid enough for an 'upgrade' then any change in sound is perceived as an improvement.
So don't use Teflon with copper either.dgta said:
When screened cable is used inside a chassis it is common practice to only connect the screen at one end. That is to prevent a ground loop. But, as Andrew implies, when the screen is only connected at one end it can only protect against electric fields. Magnetic fields are still picked up according to the size of the loop formed by the signal cable and the return current path.
If the signal return current can be made to flow in the screen, the loop area is minimised and we have protection against magnetic fields as well.
If we use an insulated input socket and connect the screen at the socket and at the first stage tube, we can minimize magnetic field pick up. But where the signal and return connections arrive at the tube we usually have a combination of grid stopper, grid-leak resistor and cathode resistor (with possibly a bypass cap) to put the signal across. I've never tried it, but perhaps those components could be bundled together to minimise loop area at the tube socket end?
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There is no "common practice", rather common Laws of Physics. You can pass a common ground wire through the shield when it makes sense, or you can ground it from one side if it would create ground loop path for some current. All depends on layout, according to laws of physics. Just remember about parasitic capacitances, resistances and inductances, that's it.
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