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XLR shell earthing


chris_bollard
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Connect the grounding tab to Pin 1. The very very rare exception is in permanent installationa where there is a specific and rational grounding scheme plan that calls for keeping the audio ground (pin 1) separate from the chassis ground (connector shell). Notice that this rare exception would almost never apply to this group.

Connect the grounding tab to Pin-1 of both ends of the cable.

gt

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In general, Glen is correct that pin 1 should be grounded to the shell. There are a couple of situations where this may not always work best though:

1. If the shell is in contact with other metal (especially electrical equipment, or metal that is grounded), you may get some induced noise.

2. There is unfortunately some poorly designed audio equipment out there that does not have pin 1 at chassis potential. Sometimes just connecting pin 1 to the chassis will cause an internal ground loop. Bill Whitlock has addressed some of these situations in his excellent "Grounding and Shielding" workshop (highly recommended).

Beyond that, connecting pin 1 to the shell is almost always best practice.

--S

Connect the grounding tab to Pin 1. The very very rare exception is in permanent installationa where there is a specific and rational grounding scheme plan that calls for keeping the audio ground (pin 1) separate from the chassis ground (connector shell). Notice that this rare exception would almost never apply to this group.

Connect the grounding tab to Pin-1 of both ends of the cable.

gt

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Assuming that the XLR connections in question are for location production sound kits, it doesn't depend on anything else.

Jump pin-1 to the grounding tab at both ends of the cable, 100% of the time. If there is a hum that a ground lift adapter or isolator can't fix, clip the jumper as a last resort, which will probably still have no affect, then repair the clipped jumper.

GT

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Assuming that the XLR connections in question are for location production sound kits, it doesn't depend on anything else.

GT

In all fairness to the Senator's overly tiresome mantra "it depends" (and I do ask myself, why be fair), this specific question of whether to ground (earth) the shell, either or both or none, is still being asked, year after year even by seasoned sound mixers who have made up hundreds of cables. In my rather long career (42 years to the day), I have heard the absolute 100% definitive answer(s) hundreds of times. The correct answer is always: 1- connect the shell to pin 1 on both the male and female end, 2- connect the shell to pin 1 on just the male (or just the female) but never to both (and female end seems to be preferred), 3- never under any circumstance connect either shell to any pins.

So, even with the utmost respect I have for Glen, on this issue I think the jury is still out. Anyone else wanting to weigh in on this, I will offer a little guidance on the relative "wisdom" of the other choices that I have heard over the years. First, we must agree that we are talking about XLR mic cable that is to be used to connect primarily microphones or line level sources, possibly up to a distance of 100' to devices, typically a mixing panel or a recorder. Short device to device interconnects may have different factors to consider. One of the reasons I have heard to NOT ground the shell, ever, is that when laid out across the set, if the shell were to come into physical contact with some other cable or connector or voltage source that is not properly insulated or grounded (and this could be a high voltage AC source), there is as risk of electrical damage or shock potential.

I would love to hear the true definitive answer that takes into account the way in which the cable is to be used in the real world.

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I would love to hear the true definitive answer that takes into account the way in which the cable is to be used in the real world.

Jeff, I don't think that the length of the cable would be a factor in whether or not to connect the XLR connector grounding tab to pin-1.

Also, if the shock hazard of a metallic shell is reason to have an ungrounded XLR, then all of our equipment carts should be fully insulated and isolated from ground.

The primary "use in our real world" factor is that we don't know what our XLR cables will be used for from time to time. They are kept on hooks, or in a Pelican case, or in a bag until needed for whatever we might want an XLR cable for. But even for XLR cables built for a specific purpose in location production sound, the shells should be grounded.

So, for the work this group does with XLR audio cables, the definitive answer is to ground XLR shells to pin-1 at all cable ends.

Glen Trew

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"So, for the work this group does with XLR audio cables, the definitive answer is to ground XLR shells to pin-1 at all cable ends."

I am very close to finally accepting THIS particular definitive answer --- what a relief it would be after all these many years to have THE answer. My comment about length was really just an attempt to clarify that we're talking about basic mic cable (and I agree we don't know exactly what it will be used for when it comes off the hook or out of the case) to differentiate from short interconnects.

I would still like to discover any potential high voltage (AC) ground - no ground issue that could occur since that is the most serious of all the scenarios I have heard over the years.

I will add that when I DO accept this answer it is unlikely I will go back to the hundreds of feet of mic cable I have and add a jumper from the shell.

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Anyone else wanting to weigh in on this

20 + something years ago I made all my XLR's with the pin 1 jumped to the shell on both ends. I would occasionally get hums or other offending noises.

Not long after that I clipped all my ground jumpers and in the past 20 or so years I can count on one hand the number of times I have had issues. Also don't know if this is relevant but all my cables are star quad.

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Thank you everyone for your learned insights. I have made all my own XLR cables for the 20 years I have been in the business. My question was prompted by a random buzz (probably from a dimmed Kinoflo light) I had in a non quad cable running from my CS3e to my 788. The cable in question is one that was "swapped" for one of mine at the end of a show. I opened up the connectors for a visual inspection and noticed that there was no pin 1 to connector shell link, though there was evidence of one having been snipped. This made me wonder if the connector earth had been in place if the if the buzz would have been present.

I swapped in another cable and the sound was clean

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Thank you everyone for your learned insights. I have made all my own XLR cables for the 20 years I have been in the business. My question was prompted by a random buzz (probably from a dimmed Kinoflo light) I had in a non quad cable running from my CS3e to my 788. The cable in question is one that was "swapped" for one of mine at the end of a show. I opened up the connectors for a visual inspection and noticed that there was no pin 1 to connector shell link, though there was evidence of one having been snipped. This made me wonder if the connector earth had been in place if the if the buzz would have been present.

I swapped in another cable and the sound was clean

It's possible this is because you were using a non quad cable and swapped for a quad cable. The star quad design came about to improve rf rejection over a twisted pair.

Just a thought.

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Never encountered hazardous voltages, but a lot of times I've encountered edison ground contacting the shell... either because of a grounded box and plate in a permanent installation, or because the shell was touching a stand or rack or conduit that had chassis-grounded equipment (including lights) mounted on it.

If the audio input is pure balanced/floating (i.e., transformer with no center tap) it's not a problem.

But if the input is grounded to the audio ground in any way, and the audio ground is connected to edison ground even through something as innocent as a video feed from elsewhere... bingo: ground loop.

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When the Shure SM-81 first came out, I clearly remember when I got my pair, that the instructions with the mic specifically said to not connect pin one to the shell on the XLR's, but that the cable supplied did, in fact, have the pin 1 jumpered to the tab (shell)...

or was it the other ways around..??

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