BigYinUK Posted September 9, 2013 Share Posted September 9, 2013 Good morning everyone A while back I reported an issue with some XLR cables I'd made up. http://www.blue-room.org.uk/index.php?showtopic=58683&st=0&p=480534&fromsearch=1entry480534 Finally found some time to have a good look at the leads/cable and have found the reason for the problem but it is (IMO) utterly bizarre. Certainly I've never seen this before. I discovered that outer (black) insulating sleeve around the red and white signal carrying wires is actually conductive. When I made up the cables, I was stripping the outer and inner sleeves (of the signal carrying cores) together and in some cases it appears that the black outer sleeve was touching the copper core. This is where the noise was coming from. I'm now avoiding this situation by stripping the sleeves off each layer at different points which will prevent this happening. The outer sleeve appears to have a resistance of approx 2.4k/m Presumably there is a good reason for this, noise reduction maybe? See attachment. http://www.jon-norris.mistral.co.uk/mcable.jpg Now got the lovely job of resoldering the eight cables all over again ! Link to comment Share on other sites More sharing options...
Brian Posted September 9, 2013 Share Posted September 9, 2013 Interesting. What part number was the cable? Link to comment Share on other sites More sharing options...
BigYinUK Posted September 9, 2013 Author Share Posted September 9, 2013 http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/530043.xml Note how the picture shows both sleeves cut at the same point as I was doing. Regards Link to comment Share on other sites More sharing options...
Brian Posted September 9, 2013 Share Posted September 9, 2013 There's your answer...Braid 80/0.10mm bare copper + conductive PE Link to comment Share on other sites More sharing options...
paulears Posted September 9, 2013 Share Posted September 9, 2013 Er.... it does say double screened in the description and Copper braid + PE shield in the details? Handy when you are running unbalanced mono for crosstalk reduction purposes? Link to comment Share on other sites More sharing options...
Electrolytic Posted September 9, 2013 Share Posted September 9, 2013 that aside is it good cable? Link to comment Share on other sites More sharing options...
BigYinUK Posted September 9, 2013 Author Share Posted September 9, 2013 ** laughs out loud ** that'll be me not reading/fully understanding the cable spec. In all fairness, not all the cables I made up were suffering with the noise, but if you cut the insulation the way the picture shows, ie both sleeves at the same point, which I guess is the way most folks would do it, then it seems that it is definitely possible that the PE sleeve can touch the conductor and cause problems. Mind you, if you were making the cables "professionally", you'd be using a proper cutting/stripping tool and this probably wouldn't happen ever - I don't have that luxury and use sidecutters which do pinch the insulators as you cut so exacerbating the problem. In an ideal situation I would usually purchase ready made up leads but in this case, I needed 4 x 25m jack to jack cables for one job ONLY so thought that if I bought a 100m reel of cable and 8 jacks this would be ideal as I could then chop the jacks off, cut the 25m cables in two, solder XLRs on and end up with 8 x 12.5 metre XLR leads which are always useful. Lesson learned? BTW Yes it seems very good quality cable, very flexible, quite tough and quiet when not suffering from the above problems :) Link to comment Share on other sites More sharing options...
paulears Posted September 9, 2013 Share Posted September 9, 2013 It's actually not that common at all - and the conductive screen touching against the copper does a good job. The plastic screen isn't that good without a copper screen too. I used to love the musiflex cable, but it wasn't as good near dimmers and lighting cable. Pretty good, but not excellent. This one could be rather useful. I'm not expert enough to comment on the common mode rejection properties, as each core is separately screened - maybe somebody else will comment on the pros and cons. Link to comment Share on other sites More sharing options...
Simon Lewis Posted September 9, 2013 Share Posted September 9, 2013 I don't think I have seen a commercial cable (admittedly mainly guitar cables) with a carbon loaded conductive plastic screen which has actually been stripped back from the central conductor... I used to look and then peel back the plastic with a thumbnail as a matter of course. Link to comment Share on other sites More sharing options...
BigYinUK Posted September 9, 2013 Author Share Posted September 9, 2013 All cables now resoldered and *silent*. Bit of practice for my soldering, some even look quite neat and tidy :) Cheers everyone Link to comment Share on other sites More sharing options...
BigYinUK Posted September 21, 2013 Author Share Posted September 21, 2013 @jplevene Thanks for that, makes sense. Regards Link to comment Share on other sites More sharing options...
TimmyP1955 Posted September 29, 2013 Share Posted September 29, 2013 It really messes up guitar cables, as the impedance drop loads the crap out of the pickups. Link to comment Share on other sites More sharing options...
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