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Topic: Wiring CAT5e to XLR (Read 4690 times) previous topic - next topic
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Wiring CAT5e to XLR

Hi All

I have some leftover CAT5e cable which I'm hoping to utilise in my studio for some short runs between CD players and other various kit to my mixer (all analogue, balanced).

This is the cable - http://www.blackbox.co.uk/gb-gb/fi/1234/12925/CAT5e-F-UTP-Shielded-Stranded-Bulk-PVC-Cable,3048m/

My question is do I connect the drain wire in the cable to pin 1 on each XLR? If so, should I connect the drain at one end only or both? Opinions online seem to differ.

The cable also has an outer aluminium/Mylar tape which I guess I don't have to connect to anything?

I've done some reading online and opinion is divided about whether to bother with the drain or not (so essentially some are suggesting nothing is connected to pin 1 at all).

Re: Wiring CAT5e to XLR

Reply #1 –
My issue with Ethernet cable is that most of it is solid conductors and tends to break at connection points.  Be very careful when you strip it not to nick the conductors.  Nicked copper conductors will break after being flexed a few times.

Regarding grounding, it depends on whether your equipment has the "pin one problem".  With properly designed equipment, where pin one is connected directly to the metal case, without running through the box, best RF immunity is with the shield grounded at both ends. 

However, much legacy and some contemporary equipment improperly grounds pin one inside the box, where it does more harm than good.  In this event, you may get hum or buzz, or RF interference with the shield grounded at both ends (or with the shield connected to pin one at all!).  If that happens, try grounding at one end only, it matters little which end. 

I'd check for two things when done.  First, with the equipment in its final location, turn up the gain fully (obviously with no CD or other item playing), listen for hum and/or buzz.  Then if good, put your cell phone near the cable and see if you get interference. 

In reality, at line level, properly designed balanced audio gear is pretty immune to noise as long as the interconnecting cable is well twisted (as cat 5 is) even with no shield at all.  People have even used unshielded cat 5 or 6 cable at mic level with good results, the tight twist cancels out both capacitive and inductive fields better than most shields, which at power line frequencies only cancel capacitive coupling anyway. 

Many years ago I connected an intercom speaker (which worked as a microphone when listening) to a loading dock 4 floors below using a pair "stolen" from the unshielded telephone riser cable in the building, as I was too lazy to run my own cable.  It was in service without issue for about 30 years, without any issues of hum, noise or crosstalk.

For further information I'd start by spending some time on Jim Brown's website: http://www.audiosystemsgroup.com/publish.htm He is one of the top authorities on grounding and has done a lot of research.  The other useful site is maintained by Jensen Transformers, worth a Google.

Re: Wiring CAT5e to XLR

Reply #2 –
schmidj - thank you for your detailed reply, very helpful and much appreciated!

The drain wire that's built into the cable - I guess that's the one I connect to pin one?

Also, I've seen a few installations where one pair is used per pin. Never understood the reasoning behind this. I intend to use one pair only, so connect one cable in the pair to pin 2 and the other to 3, leaving the remaining pairs unused. Does it make a difference?

Re: Wiring CAT5e to XLR

Reply #3 –
Yes, the drain to pin 1.

What you've probably seen is quad mike cable.  there are two pair, one side of each pair (both the same color) connected to pin 2 (high) the other side of each pair to 3(low).  Various trade names from several manufacturers.  Supposedly somewhat lower noise pickup.  I say supposedly because I've never measured it.  Probably has an advantage.  I own some quad mike cables.

You wouldn't want one pair to one pin, the other pair to the second pin.  Very bad noise/hum pickup, as the fields don't cancel that way.    Similar situation to "split pairs" in telco copper wiring, where accidentally a circuit is wired half on one pair, half on another.  Hum, noise and crosstalk like crazy.  I've had to chase those down more than once, pretty obvious when it happens.

Re: Wiring CAT5e to XLR

Reply #4 –
Look for Patch cable.
It is commonly multistranded cable hence less prone to break
TheWellTemperedComputer.com

Re: Wiring CAT5e to XLR

Reply #5 –
Thank you both! Feeling confident about the install now.

The cable is stranded.

Re: Wiring CAT5e to XLR

Reply #6 –
Quote from: schmidj on
What you've probably seen is quad mike cable.  there are two pair, one side of each pair (both the same color) connected to pin 2 (high) the other side of each pair to 3(low).  Various trade names from several manufacturers.  Supposedly somewhat lower noise pickup.  I say supposedly because I've never measured it.  Probably has an advantage.  I own some quad mike cables.
Quad cables (star-quad to be precise) are not two separate pairs, they have 4 wires twisted together. You take the two wires together which are opposing each other in the quad. The idea is that the the two wires that are taken together have a virtual center in the middle of the cable, where it coincides with the center of the other two wires. In effect, the thing behaves as if the two signals were running through wires that are in the same place. Hence the chance of inducing a differential signal gets minimised.

Star-quad is quite effective in reducing inductively coupled interference, mainly hum. But of course, if a single twisted pair is good enough already, there's little incentive to use something more complicated.

A secondary benefit of quad cables is that a breaking wire isn't going to bring down communication.

Re: Wiring CAT5e to XLR

Reply #7 –
You are quite correct about quad mic cable being four conductors twisted together, and that the opposite conductors should be connected together.  (the opposite conductors are the same color.)  Calling it two pair is over simplification.
Properly made, it "supposedly" cancels out magnetic EMI better than twisted pair, but be aware that the pitch of the twists and the symmetry of the pair has a big effect on magnetic cancellation too.  In fact, that's why the cat5/cat6 cable is as immune to EMI as it is, very tight pitch and very closely controlled geometry.  They further control crosstalk by varying the pitch of the different pair, and in some cases, particularly CAT6, adding spacers to keep the different pair further apart.

"Star Quad" is a trade name of Canare, Mogami's quad is trademarked Neglex.  There are several less expensive brands, of somewhat questionable quality also available.  Even Wikipedia seems not to recognize Canare's trademark...

Most people seem to feel the added capacitance between conductors causes some added high frequency rolloff when using long lengths.   This would be very dependent on the output impedance at high frequencies of the microphone being used.  Probably more pronounced with transformer coupled mics than direct coupled solid state mic output configurations. 

You should always consider the microphone/cable/preamp setup as a system, with no two different ones sounding the same, some similar but not exactly the same, some drastically different.  That's why you have a mic locker with a good assortment of mics, and an assortment of preamps.  Add to that the (probably less evident) effects of different mic cables, plus, often the cable from the mic jack to the mic preamp that is part of the studio permanent wiring.  Quite a few variables.

Re: Wiring CAT5e to XLR

Reply #8 –
Quote from: schmidj on
Properly made, it "supposedly" cancels out magnetic EMI better than twisted pair, but be aware that the pitch of the twists and the symmetry of the pair has a big effect on magnetic cancellation too.  In fact, that's why the cat5/cat6 cable is as immune to EMI as it is, very tight pitch and very closely controlled geometry.  They further control crosstalk by varying the pitch of the different pair, and in some cases, particularly CAT6, adding spacers to keep the different pair further apart.
This has to be viewed in the light of the interfering signal's frequency (or rather its wavelength). CAT5/6 cable is made to minimise interference in the frequency range that is used by network protocols (i.e. Ethernet). That range starts above the audio frequencies and extends to the 3-figure MHz range, depending on the speed of the network link. Crosstalk and interference are a problem particularly at the upper end of the range, because there the wavelength approaches the length of a twist. This is the most important reason why such cables are more tightly twisted, because that pushes up the maximum frequency of immunity. On the other end of the frequency range, when we deal with hum and buzz coming from the mains, the tightness of the twist is less of an issue. Manufacturing tolerances still are, however.

For frequencies in the audio range, tight twisting and/or spacers between the pairs are not going to matter much. Here, quads are effective, and shielding can help against capacitive coupling.

Quote
"Star Quad" is a trade name of Canare, Mogami's quad is trademarked Neglex.  There are several less expensive brands, of somewhat questionable quality also available.  Even Wikipedia seems not to recognize Canare's trademark...
I wasn't aware of the trademark. The literal translation into German has been in use for a very long time; maybe it was the inspiration for Canare's naming.

Quote
Most people seem to feel the added capacitance between conductors causes some added high frequency rolloff when using long lengths.  This would be very dependent on the output impedance at high frequencies of the microphone being used.  Probably more pronounced with transformer coupled mics than direct coupled solid state mic output configurations.
Capacitance does cause such rolloff, that's a simple enough fact. The details, however, are case-dependent. In most cases the output impedance of professional microphones is low enough to make this a non-problem until your cable length goes well beyond 100m. In some cases, when the output impedance is partially inductive, the cable capacitance may create resonances. In such cases you are right to point out that the setup is a system that needs to be considered as a whole. Having such a lot of variables influence the outcome in potentially mysterious ways is a pain in the ass, however. You'd wish manufacturers paid attention to minimizing such interdependencies.