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resci 15th October 2012 08:14 AM

groundless xlr
 
need advise....
after running in audio cable into a recording studio which a thought was twin pair, turns out the cable only has one ground between the 2 pairs!
at first i thought just split the ground between the 2 but but the strands may be crossed over then i thought making 1 xlr normal and another with out pin 1 (ground)?? rewiring the studio is not an option!! any suggestions??

Chris Daly 15th October 2012 10:07 AM

Hi Resci
Some info on XLR's here: XLR connector - Wikipedia, the free encyclopedia, including controversy over the shell also being wired to Pin 1

XLR's are usually used balanced, that is, there is a conductor for positive ( Hot ) and negative ( Cold ) and Ground.... 3 wires for one channel, and another 3 wires for the other channel XLR's therefore are mono type plugs - one for Left and one for Right carrying balanced wiring. see EIA Standard RS297-A

They can also be wired unbalanced - but it defeats the purpose of using balanced wiring which is very much the standard in good studio wiring. Particularly when wired just with XLR's :). Some installations i have seen depart from this, using XLR wiring part of the way ( particularly radio stations ) then using telephone switchboard wiring- dreadful :(

Cheers / Chris

resci 15th October 2012 12:47 PM

will it be ok then if i wired it pin 1 as ground (not shield) and pin2 (hot) with no pin 3 the cable consists of 2 pairs of shielded wires with 1 ground situated outside of the 2 aliminium shields... i understand that i won't have phantom power but will i still get signal into the pre amp?and will there be more noise if pin 3 is absent? and should i attach some of the wire of pin 1 to the chassis?
also thanks for your reply and your time :)

resci 15th October 2012 11:03 PM

OH! i see what your saying now! wire pin 1 to the chassis... that sounds logical thanks again :)

chrispenycate 17th October 2012 11:22 AM

You need pins 2 and 3; pin one, the shield, is a luxury (well, except for phantom power). I ran a PA multicable with only one overall screen for twenty-four twisted pairs, at mic level, and PA is generally a lot electrically noisier than studio (you're less critical, certainly, but a buzz coming out of big speakers is severely annoying anyway) for years, and was more often removing grounds to clear ground loops than bemoaning the lack of connection. How are you planning to connect – a panel with mounted XLRs on it, or flying leads? If the former, it's easy; you link your pin ones, and keep a selection of ground isolated cables (pin one not continuous). If the latter and it's foil shielded cable you're going to have to put some kind of insulating sleeve round it, anyway, right? Heat shrink or something? When you make the "Y" split in the cable add an extra, insulated wire, soldered to the drain wire at one of the XLRs and running back through the sleeve to the join and out again, all inside the sleeve; that's tougher than splitting the drain wire itself. You could do the same at the console end, even if (theoretically) this is creating a ground loop; it's short enough, and close enough that it probably won't pick up much except mobile phones, and you are banning them from the studio, aren't you?
Otherwise leave one of the pin one's disconnected.

resci 17th October 2012 01:25 PM

thank you :)
and mobile phones now band! thanks for that one too.

turk 182 7th November 2012 04:15 AM

resci
i think what you've come across is called "quad conductor" mic line it contains 2 pairs of conductors wrapped in foil shields and a single ground wire as opposed to the standard braided shield you'd find in most common single pair with a ground braid the difference is the "quad" is trading an overall ground braid with 2 foil sheilds and a drain wire
in xlr applications the quad is wired by twinning the common coloured wires together and these insulated pairs are wired to pins 2 and 3 respectively leaving the drain/ground for pin 1 i guess the premise of these is that if one shielded pair is good two is better
if you make a ground lifted xlr cable mark it visibly at both ends you would not want to mistakenly use a ground lifted cable in some applications in either a studio or pa
1:1 splitter transformers are also useful in eliminating ground loop induced noises all the the while keeping balanced connections happy

mickeymoose 7th November 2012 11:06 PM

I believe turk is right. Read up on the subject here: http://www.canare.com/UploadedDocume...ifications.pdf

turk 182 8th November 2012 01:40 AM

thanks mickeymoose
it's nice at have someone validate me
i've taken a few lashes on another thread
gotta learn how to do the copy, paste,link quote stuff all the while trying to learn how to type with more than two fingers

Pano 8th November 2012 02:50 AM

Star Quad mic cable comes with braided shield, too. We have miles of it at work, Canare brand. 2 twisted pairs inside a single shield that carries only one signal. The extra strands are suppose to be better at noise rejection that a single pair. Seems to work, but is a royal pain to wire up.

In a pinch, you can wire these to carry 2 signals, 1 on each pair. There can be some crosstalk, tho.


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