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[Andrew Broughton]

All anyone needs to know.

[Lee Buckalew]

In EE school, we were taught that shielding on communications cabling should be only connected at 1 side in order to avoid ground loops but still provide a drain for the shielding.  Shouldn't this be the case for microphone cables also?  In the case of a microphone cable, the male end would be the one to connect the shell to the shield.

Also, it seems better to me for the Pin1 signal ground to be isolated from the shield but I haven't noticed any microphone cable with a dedicated shield.

All mic and line level balanced audio cables have a dedicated shield.  They are twisted pair plus shield with the shield either being an overall foil with a drain wire or a braided/woven/wrapped shield overall.

On mic cables it is necessary that the shield be connected to pin 1 at both ends of the cable in order that they can carry phantom power.  Only in certain circumstances would you lift pin 1 of the mic cable.

It is very typical for only one shield end to be connected on line level cables in studio or rack wiring.

It is not normal for pin 1 to be connected to the case of the XLR.  There are many situations where this is not preferred.  Because of this it is more common for there to be a switch on the component chassis that allows the connection between pin 1 and case to be made or broken as required.

Lee

[Geoff Doane]

And that response tells me all I need to know.

From Neumann per the link above;

[snip]
 
There is no reason why the conductive shell and microphone housings should not be connected to the shield of the microphone cable directly via the terminal expressly provided by the connector manufacturer for this very purpose. With this in mind, there is also no reason why you should shy away from adding this connection (jumper between pin 1 and the shield terminal) yourself on improperly wired existing cables...  "

There's a very good reason why they shouldn't be connected, as Ivan points out.  Maybe the Germans don't have to bond their electrical raceways to electrical ground, but we do have to in North America, and I have seen the Gotham mic cables which Neumann includes with the U87s cause exactly this kind of problem in a recording studio.

Further on in the Neumann thread Bob quoted, somebody mentions using Neutrik EMC XLRs instead of regular ones if RFI is likely to be a problem.  They ground the shell through capacitors, which will provide RF shielding, but not cause a ground loop.  Probably the best of both worlds, although at some increased cost.  I've only read of one actual occurrence of RF getting into cables because of ungrounded XLR shells (a recording session on the CN Tower in Toronto), but I've never experienced it myself.

Contrary to the advice in that Neumann thread (to connect pin 1 to the case of all your existing cables), the Gotham cables don't actually connect the shell to pin 1, they have 3 insulated conductors for the three pins, and then a braided shield for the shells.  By themselves, they would be OK, but every microphone I've ever seen (including the U87) connects pin 1 to the mic case, and that causes a ground loop with those cables.

GTD

[Art Welter]

I guess that was long as every piece of gear in the system is properly designed not to have pin 1 problems, then you "might" be OK.

I still stand by my "understanding and experience" and will NEVER connect pin 1 to the shell of an XLR cable or on a jack on a wall plate.

Why invite problems?

But maybe that is just me-------------

Me too.

Connecting the shield to the microphone case does help shield the microphone element, but there is no good reason to make that connection other than at the microphone itself.

Art

[duane massey]

+1 per Ivan. I'm not an "educated" electronics guy, but my 45 years in the business taught me a long time ago that connecting the shell of a mic cable to the shield gained nothing but could (and did) cause problems.

[Bob Leonard]

I have to agree to disagree. Yes, I have had problems resolved by lifting pin 1. No I have not had problems specifically caused by grounding the connector shell to the cable shield.

[Ivan Beaver]

I have to agree to disagree. Yes, I have had problems resolved by lifting pin 1. No I have not had problems specifically caused by grounding the connector shell to the cable shield.

Or as the saying goes-"you just haven't done it long enough"

[Andrew Broughton]

I have to agree to disagree. Yes, I have had problems resolved by lifting pin 1. No I have not had problems specifically caused by grounding the connector shell to the cable shield.

Have you read the article I linked? Basically grounding the shell fixes RF issues, but can create ground loop issues. Check out the article if you haven't already.

[Luke Geis]

I know in the guitar amp building world, that any " signal " that passes through a coax cable within the amp has the shield connected to ground at only one end; not both..... This is to reduce RF introduction and ground loop potential.

I could see where having only one end of the XLR cable shield connected to the shell would be effective in eliminating RF introduction, but have never had an instance where RF and or crosstalk was an issue. I like the idea of being able to lift pin 1 if needed, although I find I need to less and less these days.

[Bob Leonard]

Maybe we're not speaking the same language. I do not condone grounding pin one (1) to the shield and the shell of the connector. What I do condone is using the cable shield as a ground to the connector shell at either one or both ends. This has been my standard practice for going on 50 years (Ivan) when building my own cables. This is a chassis ground/earth which has never been a problem for me in the past or present as this ground has no attachment to pin #1. Of course this connection can only be made using 3 wire cable that is shielded. Please keep in mind that my first experience with XLR type cables dates back to the early 60's when XLR cables were used for much more than just microphones, and was at that time common practice.

In short order Wiki happens to reflect my understanding, so to each his or her own concerning this matter, and, as long as pin 1 is not grounded to the shield I don't see where there is an issue, especially concerning RF interference where this technique should be desirable.

"Although covered in industry technical standards, there is still some disagreement on the best way to handle the use of pin 1 for grounding (earthing). The main controversy is whether the shell of the connector should be connected to pin 1 or the shield, or left floating. AES standards recommend that shells of cable-mounted connectors should never be connected to pin 1 or the shield, because inadvertent contact of the shell with another grounded surface while in use can create unwanted current paths for fault current, potentially causing hum and other noise. On the other hand, equipment containing active circuitry should always have pin 1 connected to the conductive enclosure of the equipment as close as possible to the point where the signal enters the enclosure.

The argument centers on the radio frequency shielding provided by the shell of the connector, which may be reduced if it is left floating. An alternative solution is to connect the shell to pin 1 and the shield through a small value capacitor, providing RF shielding but allowing very little audio-frequency current to flow. This capability can be built into a fixed jack or a cable terminated with XLR connectors."
 
Luke,
There are multiple grounding points inside of a guitar amplifier and within each stage of the amplifier. Additionally the incoming A/C shares that ground (chassis) in modern amplifiers, and with a switch and cap in most amplifiers prior to the early 70's. The purpose is of course to insure a common ground circuit within and between the amplifier stages and A/C eliminating noise and 120 and 60 cycle hum. The shielded cable you mention is generally used from the 1/4" input jacks to pin 2 of the first stage preamplifier tube, the input. This is actually a practice that came about in the early 70's, a result of faster production and sloppier point to point wiring,
One end of the cable shield will always ground to the outer shell and one side of the potentiometer. From that point the pot is grounded not only to the chassis mechanically, but also by using a solid wire from chassis ground. In amplifiers prior to the early 70's you will not find this shielded cable specifically because the point to point wiring was done in a more meticulous manner. What you will find in a Fender amplifier from the 60's is a single red wire running from the input jacks to pin 2 of the first input stage 12AX7. Neater and properly routed wiring eliminates the need for the shield. Just an FYI.   

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