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Title: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett 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?
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett 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???
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Geoff Doane 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
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Kevin Graf 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.
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett 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.
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Kevin Graf 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
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Kevin Graf 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.
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett 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?   

Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Jordan Wolf on June 01, 2014, 03:19:08 PM
Rick,

Bill Whitlock (of Jensen Transformers renown) has a great presentation on system grounding (http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf).

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. :-)
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett on June 01, 2014, 04:40:07 PM
Rick,

Bill Whitlock (of Jensen Transformers renown) has a great presentation on system grounding (http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf).

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 ...
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Steve M Smith on June 01, 2014, 05:35:36 PM
If you have a wallbox (permanently installed snake) in your studio, by code the metalwork must be bonded to electrical ground.

Really?  For microphone signal level wiring?


Steve.
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett on June 01, 2014, 06:27:06 PM
Rick,

Bill Whitlock (of Jensen Transformers renown) has a great presentation on system grounding (http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf).

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. :-)

Well I know how to electrically wire my new studio when the time comes! lol - and I bout sh!t myself when his article called out my ebtech line level converter as useless ... no info on mic cable with more than two cores tho. 
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Rich Barrett on June 01, 2014, 10:25:45 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

I JUST got a reply from JIM BROWN ... read some of his papers and decided to email the man - very of nice of him to respond in detail. His reply as follows ... Enjoy!!

Quote
Hi Rich,

Sadly, many of those who manufacture equipment have yet to see the
light. I have a lot of those Gotham cables left over from 40 years ago,
and had to clip the Pin 1 to shell jumper. They are otherwise very good
cable, but no better than Belden 8412 and some excellent Gepco cables.

The AES Standards for audio wiring (written jointly by Neil Muncy, Bill
Whitlock, Bruce Olson, and myself with support from other members of the
AES Standards Committee Working Group on EMC) all call for the following:

For balanced wiring:

Pin 1 - Shield
Pin 2 - Signal High
Pin 3 - Signal return

ONLY inside ACTIVE equipment (including microphones), Pin 1 shall ALWAYS
be bonded straight to the shielding enclosure (usually the chassis).
"Active equipment" means something that includes electronics.

Outside equipment, there should NEVER be a connection between Pin 1 and
the shell. In other words, cables should NEVER have a connection between
Pin 1 and the shell. Such a connection is provided inside the equipment.
For purposes of these Standards, snake boxes, patch panels, and
multicables are treated as cables, even though their terminations may be
in boxes. A mic splitting system would be "active" only if it included
electronics -- for example, a digital snake system that multiplexes many
mic circuits on a single circuit.

Those Standards are AES48, AES54-1, AES54-2, and AES54-3. They are free
to download for AES Members. If you're not a member, you should be. In
addition to access to those Standards, you'll become a member of your
local section, where you can learn from other professionals in your area.

Regards, Jim Brown
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Brian Jojade on June 02, 2014, 11:32:16 AM
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?

The audio signal is passed on pins 2 and 3. The shield is simply there to drain off any external EMF that may be around.  The 3rd wire paralleled with the shield would be beneficial for your phantom power in the event that the shield conductor is broken in any way. 

On the cables, NEVER connect anything to the shell of the XLR.  I always have my cables wired with 3 all 3 conductors.  If there's a need to break ground for whatever reason, I use short adaptors for that purpose.
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Kevin Graf on June 02, 2014, 12:10:03 PM
Rick,
Bill Whitlock (of Jensen Transformers renown) has a great presentation on system grounding (http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf).
It's definitely worth a read, then a re-read.  ................................

There is an Audio/Video presentation of a Bill Whitlock seminar.

"Bill Whitlock Presented “Effective Audio Grounding Design” In Chicagoland"
http://www.prosoundweb.com/article/bill_whitlock_presenting_effective_audio_grounding_design_in_chicagoland_ne/technician

*********************************************
It is mostly audio, the video is the PowerPoints in the above link. It's about 1 hour 45 minutes long and still only covers 2/3 of the paper.
It is a large file, and the link will expire on June 11.
The tech expo was a success!!  Many of you have requested, and Bill Whitlock’s power and grounding presentation can be found here.
http://soundmarketingreps.com/bill-whitlock-presentation-available/
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Geoff Doane on June 02, 2014, 03:42:30 PM
Really?  For microphone signal level wiring?


Steve.

Steve, I'm a bit late getting back to you on this because I wanted to get my facts straight.  I'm working on a project at the day job right now that involves several P.Engs, so I asked one of them about it.  All troughs and wallboxes must be bonded to electrical ground regardless of what wires will be in them.  It may be because an electrical inspector doesn't know what voltage is on any of those wires, he just wants metalwork grounded. 

It's also a safety thing on another level.  If some kind of fault occurs in the audio equipment, or if a totally unrelated electrical wire gets snagged on the trough, you don't want that voltage to be conducted all over the plant by what is assumed to be "low voltage" trough.

In our particular facility, there is a slight exception made to this rule.  All equipment racks are connected to "technical ground", which in turn is connected to electrical ground at the ground point for the building.  This prevents the inevitable electrical ground currents from contaminating the technical ground.  The equipment racks sit on wooden plinths to insulate them from casual contact with anything else metallic, and special care needs to be taken with any ventilation ducts at the top of the racks.  All the equipment in the racks is powered from isolated ground outlets, with two grounds: technical that goes to the equipment, and electrical which grounds the conduit.  We don't let the conduit touch the racks.

GTD
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Kevin Graf on June 02, 2014, 05:08:49 PM
Once we get into AC power wiring, Middle Atlantic has an execlent paper.

"Power Distribution and Grounding of Audio, Video and Telecommunications Equipment" White Paper

http://www.middleatlantic.com/resources/white-papers.aspx
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Steve M Smith on June 02, 2014, 05:27:55 PM
Steve, I'm a bit late getting back to you on this because I wanted to get my facts straight.  I'm working on a project at the day job right now that involves several P.Engs, so I asked one of them about it.  All troughs and wallboxes must be bonded to electrical ground regardless of what wires will be in them.  It may be because an electrical inspector doesn't know what voltage is on any of those wires, he just wants metalwork grounded.

Thanks for replying.  It would appear that compared with us here in England, the US has a lot more regulations and inspections than we do.

Here, if someone wanted a permanently installed, metal boxed multicore. it would just be fixed to the wall, plugged in and used.

Domestically, we have rules about ground bonding metal pipework and public buildings require all exposed metalwork to be grounded, but that's about it.


Steve.
Title: Re: wiring 3 conductor mic cable to 3pin xlr ???
Post by: Geoff Doane on June 02, 2014, 08:16:14 PM
Thanks for replying.  It would appear that compared with us here in England, the US has a lot more regulations and inspections than we do.

Here, if someone wanted a permanently installed, metal boxed multicore. it would just be fixed to the wall, plugged in and used.

Domestically, we have rules about ground bonding metal pipework and public buildings require all exposed metalwork to be grounded, but that's about it.

Well, I'm in Canada, not the US, but the rules are still more alike than they are different.

While I was talking to the Engineer about this, I pointed out that there is no special grounding for metal door frames, as opposed to wire troughs and raceways.  "Yes, but they don't have wires in them", was his reply. So the regulations aren't exactly consistent or 100% logical.

GTD