ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 [2]  All   Go Down

Author Topic: wiring 3 conductor mic cable to 3pin xlr ???  (Read 1173 times)

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1124
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #10 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.
Logged

Rich Barrett

  • Newbie
  • *
  • Offline Offline
  • Posts: 48
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #11 on: June 01, 2014, 06:27:06 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. :-)

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. 
Logged

Rich Barrett

  • Newbie
  • *
  • Offline Offline
  • Posts: 48
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #12 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
Logged

Brian Jojade

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 393
    • HappyMac Digital Electronics
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #13 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.
Logged
Brian Jojade

Kevin Graf

  • Full Member
  • ***
  • Offline Offline
  • Posts: 122
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #14 on: June 02, 2014, 12:10:03 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.  ................................

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/
Logged
Speedskater

Geoff Doane

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 549
  • Halifax, NS
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #15 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
Logged

Kevin Graf

  • Full Member
  • ***
  • Offline Offline
  • Posts: 122
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #16 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
Logged
Speedskater

Steve M Smith

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1124
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #17 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.
Logged

Geoff Doane

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 549
  • Halifax, NS
Re: wiring 3 conductor mic cable to 3pin xlr ???
« Reply #18 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
« Last Edit: June 02, 2014, 08:56:59 pm by Geoff Doane »
Logged
Pages: 1 [2]  All   Go Up
 


Page created in 0.147 seconds with 23 queries.