How To Wire An XLR Connector Properly

On the face of it the title of this blog may seem like teaching your parents mothers to imbibe an ovum. After all, connecting a piece of wire to that most universal of audio connectors is simple enough, is it not?

Well it is. But to do it well and not making a mess of it in the process does take a little practice and the learning of a few tips. Ok, I accept pre-wired cables are readily available, but sometimes you will have to reach for the soldering iron  to make a bespoke cable up, or repair an existing one. So when you do, you may as well make sure the job properly. (Top Tip: For your own sanity steer clear of the IDC connector versions of the XLR – they are simply horrible)

The accompanying photos are all real-world examples of good and poor XLR wiring, forming a step-by-step guide on good practice and what not to do.

We want to have something a bit better than this. Why? I mean the right wires are connected to the right pins. Screen to 1 (X) Hot to 2 (L) and the Cold to 3 (R). But just look at it! Blobby solder, no overall screen sleeving and MAINS cable being used.

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For the purposes of this article I will assume you have some soldering experience, know the melting point of your chosen solder and thus the temperature of the soldering iron. I also assume that you are familiar with the safety aspects of both soldering and handling solder.

Tools For The Job
You will also require:

  • A knife.
  • Side cutters and pliers of a suitable size for the job i.e. not ones designed to cut or grip mains cable. Tube expanders (also known as "Helleman" pliers).
  • Mineral oil for lubricating the rubber tube.

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  • A rubber sleeve, known by the brand name "Helleman" sleeves, of an unexpanded diameter just smaller than the outside diameter of the cable.
  • Suitable sleeving to slide over the earth wire. Silicon sleeving, universally known as “Symol” after the brand name, is recommended, but you can also use a smaller diameter version of the rubber sleeving used to go over the cable sheath.
  • A decent quality soldering iron with a bit that is the right size for the job – i.e. not a brazing bit!
  • Solder.
  • Something to hold the connector pins. I use a “helping hands” to hold the connector but I have seen others use small bench vices, bulldog clips screwed to blocks of wood or the opposite sexed panel mount connector set into a block of wood. Anything that works for you in holding the connector steady whilst you solder it is fine. Trying to hold it by hand or chase it around the bench as you fill the solder buckets is not recommended.

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  • Depending upon your chosen model of XLR connector a small screw driver to assemble it. Top Tip: Given the choice, opt for Neutrik screw-less types every time: Either the NC3 X or XX series.

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The secret of a good XLR termination is in the prep of the wire that will be connected to it.

First cut about 3cm of the sheath off, being careful not to cut the braid screen, if the cable has a foil screen remove this.

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If the screen is a braid type, separate into the individual strands and then twist it into a single thicker length. If the screen is a foil/drain wire combination then remove the foil screen and separate out the drain wire.

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Sheath the screen wire using suitable insulating sleeving (heat-shrink, silicone or rubber sleeve)
Cut the insulation of the screen and the two conductor wires back. If it is a stranded conductor then twist the strands to make a solid conductor.

Tin all three conductors. Note: In the pictures “Starquad” cable is being terminated. This is a four-wire version of balanced audio cable. Two pairs of wires are created from the four in the cable by twisting them together. However the principle of soldering it to the XLR is the same as standard twin/earth audio cable.

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Depending upon the XLR connector design, slide those parts onto the cable that will need to be fitted prior to soldering the pin section on. This very important if you want to avoid the subsequent swearing when you go to assemble the connector!

Using tube expander pliers and mineral oil slip a rubber sleeve over the join where the cable sheath meets the inner wires. Many people skip this step deeming it unnecessary, but doing so will ensure the prepped wire not only looks nice but more importantly completely insulates the screen and gives the connector chuck a better grip on the cable. And we are not at home to Mr Cut-corners are we?

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Fill each solder bucket of the connecter about 75% full of solder.

Solder each wire to the correct bucket ensuring there are no dry joints and that all wires are seated in the bucket with no ends or strands hanging out.

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Assemble the connector ensuring that the cable is adequately strain-relieved and that the individual wires have some play between the cable clamp and the solder buckets.

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Job done!

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You can see that is more than just three soldered joints. There is quite a bit going on within the body of the connector: Flexibility, connectivity, strain-relief and insulation.

Ok. Now you have done one, repeat for the other 50 or so on the back of that mixer!