Cat 5 has no foil or drain wire, Can I attach 15U to something else?

[pingpongcomputer]

What should I do about 15U since my cat5 cable has no drain wire or foil?

[Paul Birkeland]

Contact replacementparts(at)bottlehead(dot)com and let them know.  There is CAT5 for the speaker kit that has no foil or drain wire, then there is the CAT5 that you're supposed to have with foil and the drain wire.  I would strongly recommend waiting for the correct wire to arrive before proceeding.

[pingpongcomputer]

I shouldn't have, but I already went ahead.  Is there a fix, or do I need to de-solder everything and wait for the correct cat 5?

[Paul Birkeland]

I don't know, you'll have to smoke it and see.

[mudvin]

If you have no foil in your cable then it is likely unshielded.

I would hazard a guess that it may work fine because the cables are still twisted pair inside, which should do a pretty good job of deflecting hum / noise by itself.

The only way to tell would be to fire it up and listen

[Deke609]

Blue Jeans Cable, a popular maker/retailer of audio cables, has an article on cable shielding and hum rejection: http://www.bluejeanscable.com/articles/humrejection.htm


I can't vouch for the results of their experiment, but I've come across at least one other "study" (I use that term very loosely here) that found that double shielding with braid offers more protection than various combinations of twisting wires and single shield layers.


But I don't know whether the signal cable in your amp would be exposed to enough outside interference for shielding of any type to make a difference. My suggestion would be to build the amp now with the cable you've got and order the replacement length of cable from BH (and if the kit supplies nylon ties for the cable and you've already used them, I'd ask for replacements of those as well). This way you can enjoy your amp sooner, and if you're curious down the line about what effect if any the shielded cable would make, you can swap in the new cable and have a listen.


cheers,


Derek

[mudvin]

I'm not sure that Blue Jeans Cable is correct with their base assumption in that article, that twisted pair only rejects hum on a balanced setup.

Looking around, twisted pair seems to be part of the original telephone circuit patent, by Alexander Graham bell, in which he explains how it works.

Regards, Rob

[pingpongcomputer]

Thanks everyone for the info, I finished the build.  It passed all resistance and voltage checks and I'm not getting any extra noise.  Incidentally an electrical engineer from Shure overheard me talking about it and said not to worry.  Bottlehead got in touch and is sending me the correct shielded CAT5 cable which I will install if I go back in for tweaks.