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Psilonaught

Conductive Aluminium Tape ok to use for cable shielding?? DIY cable question.

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Posted (edited)

I'm about to order 15m of 0.7mm pure silver cable for a x2 pair XLR cable build, and had a question about the shielding/ ground connector on an XLR socket.

I intend to run a single run of wire, insulated in teflon, for each of the hot and cold pins, and then use Conductive Aluminium Tape to 1) shield and 2) create a twist of cable to solder to the ground pin.

I will then encase everything in 8mm PVC sleeve (more teflon seems overkill and a waste of money).

Does this all sound sensible?

I was going to use copper braid but I think it will be hard to pull the outter PVC sleeves over the top of braid.

Edited by Psilonaught

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Super Wammer

I would not be to keen on the Silver tape, as you have a rubber adhesive insulating each layer. Rather than a screen you could have the effect of quite a long loop. I would prefer braid as each layer is in electrical contact with its neighbour.

Alan

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What you ask is possible regardless of the foil tape. I didn't read everything about the foil tape.

Follow the XLR arrangements shown here: https://www.rane.com/note110.html

Don't forget to actually read it, not just look at the pictures.

For the connection to pin 1, it may be best to use a bare copper wire running the length of the cable, so you can solder it, not the tape (many tapes aren't solderable) - but it's connected to the tape where the tape wraps. You will have to ensure there is metal on metal contact between the foil tape and the ground wire you run somewhere. I'm saying this as many tapes are only conductive on one side and I wish you to avoid using an extra wire only to have it insulated on the sticky side of the foil tape. However, if you are smart over how you use the tape, you can ensure conductor on conductor arrangements easily.

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Braiding shield will be separate to sleeving.

I searched RS Components, but the shielded sleeves are only sold in long expensive reels. If I choose 10m instead, the following search shows the options:

https://uk.rs-online.com/web/c/cables-wires/cable-accessories-ties-tools/cable-sleeves/?applied-dimensions=4294861397,4294848544

From there, you'd have to pick the inner diameter that meets your requirement, then be mindful of the outer diameter so that you buy outer sleeving that will fit over the top.

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use a shielding with a low capacitance (dielectric) is my advice. Go from here.

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Moderator

I agree with Alan here. As the tape is effectively insulated on one side and adhesive on the other, you are going to create a sort of coil if you wrap it spirally around the signal wires. Not to mention that aluminium is not ideal in the first place. Also, it may be solderable, but it's designed for things like heating ducts, where you can solder a grounding wire to it once it's stuck onto something. If you just 'scrunch up' the end, you're going to have a mixture of aluminium and rubber adhesive, and I wish you luck trying to solder that without it ending up a right mess.

Assuming it's low level, then you need effective, continuous screening. The only sensible way is to use a metal screen. Try here: https://www.copperbraid.co.uk/tubular-shielding-braids/?gclid=EAIaIQobChMIo7qEzd3R4QIVDpztCh3NmwRLEAMYASAAEgJ-SPD_BwE they have various diameters available to buy online. I've not used them, but it looks ideal for what you need. As long as you tidy the ends first, it won't be a problem to run a 'normal' insulating braid over the top of this if you want. To make it really easy, trim, tidy and 'tin' the connecting wires first, then heat shrink over the ends of the metal braid before you put the insulating braid over (and then heatshrink over the lot at each end). Time consuming, but way, way better.

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Or this one (same supplier) https://www.copperbraid.co.uk/product/copper-stocking-braid-6-mm2/

It looks like about £20 for a 5m length with VAT and bits and is more expandable.

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There's this. https://www.ebay.co.uk/itm/bgb13-1m-3-3ft-13mm-Flat-Tinned-Copper-Braid-Sleeve-Screening-Tubular-Cable-DIY/301570180336?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 

BTW, if you wrap the whole screened cable in PTFE tape, it holds the whole thing together and makes sliding anything else over it a lot easier.  I also use it to cover the bare ends of cables to slide heatshrink or expandable braid over, then take it off to solder the wires.

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On 15/04/2019 at 13:37, awkwardbydesign said:

There's this. https://www.ebay.co.uk/itm/bgb13-1m-3-3ft-13mm-Flat-Tinned-Copper-Braid-Sleeve-Screening-Tubular-Cable-DIY/301570180336?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649 

BTW, if you wrap the whole screened cable in PTFE tape, it holds the whole thing together and makes sliding anything else over it a lot easier.  I also use it to cover the bare ends of cables to slide heatshrink or expandable braid over, then take it off to solder the wires.

Good shout!

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I've postponed this build until my new teflons caps in my preamp settle down. They have turned a very neutral system bright. Cap rolling is SO frustrating!

Adding silver right now might compound the problem.

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Moderator

If they're those Russian ones, assuming they're the same values, give them plenty of hours. They look very large, so presumably are rated for a much higher voltage than you need. In which case as they're likely to have been sitting around for ages, reforming will take a while.

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Yeah ft-3. They are bloody HUGE!

They are .22 and they replaced 0.33 sonicaps however photos of the preamp I have on the manufacturer site shows 0.22 so hoping the brightness isn't down to that. Not sure why they changed the value. I'm tempted to try some Jensen copper oils but I need to try and be patient! 

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It would make a poor balanced interconnect cable indeed.  It would have very high Shield Current Induced Noise (SCIN)! The best balanced interconnect cables are Shielded Twisted Pairs (STP) with a braided shield. The best cables have very symmetrical center conductors with relationship to the shield. It takes big expensive machines and an excellent Quality Control department to make the best cables. Just stick with the major bulk cable manufactures.

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