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Author Topic: wiring 3 conductor mic cable to 3pin xlr ???  (Read 21418 times)

Rich Barrett

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wiring 3 conductor mic cable to 3pin xlr ???
« on: May 31, 2014, 07:36:07 PM »

I have a home studio so none of my runs are over 30' nor do I anticipate a rats nest of different voltage wires laying on top of each other. I bought some Gotham GAC-3, 3 conductor mic cable to try out with Neutrik NC3's. I used some of Gotham's 4 conductor wire for headphone rewires and fell in love...

long story short, they are a foreign company and the wiring suggestion on their website has me baffled. (image attached) - it reads as follows;

Quote
GAC-3 XLR-Connector:
   
1 = green pin 1
2 = brown pin 2
3 = white pin 3
4 = screen pin 1

Microphone wiring diagram (3 conductor cables wiring)

We do not recommend to solder the XLR-Connector shell to pin  1 (Ground,)  since the connector, once not pluged in, could make contact to a different ground, being loose. Contact Pin 1 to ground shell is only made once a connector is actually pluged in!

My mixer (Yamaha 02r) manual states the XLR inputs conform to IEC 268 standards (pin 1 ground, pin 2 hot, pin 3 cold) and this is for condenser mics so phantom power is applied.

If it were a normal 2 conductor mic cable, I'd have my cables done. Instead I'm sitting here with my soldering iron and am not sure what to do ... My thoughts are;
pin 1: green
pin 2: white
pin 3: brown
shield: connected to mixer side xlr shell only

BUT if I do that, I feel I'm breaking the signal balance by using the green conductor for pin 1. Any ideas?
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Rich Barrett

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #1 on: May 31, 2014, 08:50:52 PM »

I have a home studio so none of my runs are over 30' nor do I anticipate a rats nest of different voltage wires laying on top of each other. I bought some Gotham GAC-3, 3 conductor mic cable to try out with Neutrik NC3's. I used some of Gotham's 4 conductor wire for headphone rewires and fell in love...

long story short, they are a foreign company and the wiring suggestion on their website has me baffled. (image attached) - it reads as follows;

My mixer (Yamaha 02r) manual states the XLR inputs conform to IEC 268 standards (pin 1 ground, pin 2 hot, pin 3 cold) and this is for condenser mics so phantom power is applied.

If it were a normal 2 conductor mic cable, I'd have my cables done. Instead I'm sitting here with my soldering iron and am not sure what to do ... My thoughts are;
pin 1: green
pin 2: white
pin 3: brown
shield: connected to mixer side xlr shell only

BUT if I do that, I feel I'm breaking the signal balance by using the green conductor for pin 1. Any ideas?


I found this on a resellers website pertaining to the same cable...

Quote
Why three conductors for an audio signal? Here are some answers: Grounding/shielding: With the third conductor put to ground, together with the two shields, we have increased RF-rejection to 115dB (20dB better than standard) at 25 kHz. This fact has also been conformed at the AES-paper held by Mr Neil A. Muncy ("Noise Susceptibility in Analog + Digital Signal Processing Systems") in November 1994.
 The GAC-3 was named the best performing microphone cable available. Round Construction: 3-conductor constructions are round constructions, and since the cable has the freedom to move in all directions, especially on the strain relief of a connector, the cable will survive more movement cycles. Phantom Power: The 3rd conductor can be wired as a drain wire for a reliable connection of phantom power to the
 microphone without affecting the shield. Each of the three conductors consists of 96 (!!) strands of 0.05mm copper wires being the finest stranding for audio cables available which gives you improved flexibility, better signal transport and longer lifetime (moving cycles).
 (Heavy duty version with 5.8mm Ø also available).

using the 3rd conductor as a drain wire???
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Geoff Doane

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #2 on: June 01, 2014, 10:35:33 AM »

I found this on a resellers website pertaining to the same cable...
using the 3rd conductor as a drain wire???

Yeah, it's a bad idea, and here's why.

If you're just running from a mic to console, no problem.  But if the case of that XLR touches another ground, and your console is fussy about the "pin 1 problem", you are likely wind up with hum.  If you have a wallbox (permanently installed snake) in your studio, by code the metalwork must be bonded to electrical ground.  This can easily create a ground loop, and the noise that results.

I've seen this happen in a studio with the cables supplied with Neumann mics.  They were wired similarly to what you describe, except pin 1 wasn't connected to the case (inside the XLRs).  But it was connected inside the microphone (every mic I've ever seen does this), and that resulted in the wallbox ground contaminating the audio ground.

These days, with more fault tolerant consoles, you may get lucky and not have a  problem, but why temp fate?  There is no upside to this wiring scheme, despite some marketing hype.

GTD
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Kevin Graf

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #3 on: June 01, 2014, 10:51:35 AM »

First: that vendor's reference is incorrect.  Neil Muncy (RIP) never suggested that.
Second: In his later work on Shield Current Induced Noise (SCIN) he showed that a 3rd wire or even a bare drain wire was a bad idea.
Third: AES Standard 54 states that a cable's shield should not be connected to the shell for the reasons listed in the above posts.

So what would I do?
Connect the Green wire to pin 1 at both ends.
Connect the shield to pin 1 at the send end.
Not buy anymore of that cable.
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Rich Barrett

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #4 on: June 01, 2014, 12:37:46 PM »

Thanks for the help thus far guys ... In my situation, the cables are for mics installed at specific locations in my home studio so I don't have to worry about grounding out or adding extension cables. And they won't be used for anything else as long as my studio is here.

I was just confused by the mfg's schematic which according to how I was taught to read them (US military) shows the shield EXTERNALLY connected to ground on the mixer end, NOT through pin 1.

Kevin, am I right in understanding the reason why you would only connect the shield to pin 1 at the SEND end is because of a possible difference in potential between pin 1 ground in the mixer and mixer common ground?

And thanks for the heads up on SCIN - gonna see if I can find a free copy of that paper floating around ...



First: that vendor's reference is incorrect.  Neil Muncy (RIP) never suggested that.
Second: In his later work on Shield Current Induced Noise (SCIN) he showed that a 3rd wire or even a bare drain wire was a bad idea.
Third: AES Standard 54 states that a cable's shield should not be connected to the shell for the reasons listed in the above posts.

So what would I do?
Connect the Green wire to pin 1 at both ends.
Connect the shield to pin 1 at the send end.
Not buy anymore of that cable.
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Kevin Graf

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #5 on: June 01, 2014, 01:22:44 PM »

XLR pin 1 is a shield and is only connected to the chassis at the connector.  It's true that the Main Audio Ground (or star point) is also connected to the chassis. But that's their only connection together.

Jim Brown has all the articles on his website.
http://www.audiosystemsgroup.com/publish.htm
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Kevin Graf

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #6 on: June 01, 2014, 01:56:30 PM »

******************************************
Kevin, am I right in understanding the reason why you would only connect the shield to pin 1 at the SEND end is because of a possible difference in potential between pin 1 ground in the mixer and mixer common ground?
******************************************

Some experts recommend connecting the shield at both ends even in the largest multi-building movie studios.
Some experts recommend connecting the shield at only at the send end, when each end has a different AC power source.
Some experts recommend connecting the shield at only at the send end in all situations.
Some experts recommend connecting the shield at only at the send end and using a hybrid connection at the receive end.
(the hybrid is a small capacitor)

So take your pick.
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Rich Barrett

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #7 on: June 01, 2014, 02:24:57 PM »

Some experts recommend connecting the shield at both ends even in the largest multi-building movie studios.
Some experts recommend connecting the shield at only at the send end, when each end has a different AC power source.
Some experts recommend connecting the shield at only at the send end in all situations.
Some experts recommend connecting the shield at only at the send end and using a hybrid connection at the receive end.
(the hybrid is a small capacitor)

So take your pick.

LOL - that's pretty much as concrete an answer as anyone else on other forums has to offer.

In my mind, I think of the shield as metal conduit and the conductors as wires going through it. So I would think that I want the potential of the shield to be the same as the cleanest ground in the circuit which to me is pin 1. (Assuming a chassis ground is not connected in the circuit)

I say that because if I remember correctly, from what I previously read while doing research about something else, that in lower quality gear, pin 1's path to ground is through the circuit board ground plane, or common ground which has a higher potential than chassis ground so to connect two devices together (one high quality, one inferior), grounding each other through the shield, it will induce noise.

Granted a mic has no ground of its own which is what my cables are connecting to.

I'm using phantom power on all my mics so I'm stuck using pin 1 ...

That said, would connecting the green conductor to pin 1, which is intertwined to the other two conductors break my line balance? Or is it inert because it has the lowest potential out of the 3 conductors and will therefore help absorb any stray EMF those conductors create?   

« Last Edit: June 01, 2014, 02:30:13 PM by Rich Barrett »
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Jordan Wolf

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #8 on: June 01, 2014, 03:19:08 PM »

Rick,

Bill Whitlock (of Jensen Transformers renown) has a great presentation on system grounding.

It's definitely worth a read, then a re-read.  Keep it in the bathroom, too...you never know when you might get the urge to read about grounding. :-)
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Jordan Wolf
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Rich Barrett

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Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #9 on: June 01, 2014, 04:40:07 PM »

Rick,

Bill Whitlock (of Jensen Transformers renown) has a great presentation on system grounding.

It's definitely worth a read, then a re-read.  Keep it in the bathroom, too...you never know when you might get the urge to read about grounding. :-)

Great read, am reading it now ...
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ProSoundWeb Community

Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #9 on: June 01, 2014, 04:40:07 PM »


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