XLR Patch Bay - grounding

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Paul G

Well-known member
Joined
Mar 2, 2009
Messages
75
I putting together a XLR patch bay to make accessing my pres a bit easier.  I'm also going to pick up a feed to FX from the output side of the PB.  Am I looking a potential ground loop problems here?  If so, what would be the best solution?  I'm using pre-punched rack panels with the jacks hard wired.  In to the pre, out from the pre and then into my interface.  Thanks.

Paul ;D
 
Hi Paul,

In this application you're effectively using it as an "isolated" patch- i.e. with XLR chassis plugs/sockets Pin 1 is connected only through the plug/socket itself and doen't actually touch the metal chassis of the patch panel (as long as the plugs/sockets you use as patch leads don't have pin 1 linked to the shell)

This is the same as plugging an XLR cord directly into the equipment and sending it to the following piece of equipment.

Providing-

a. the outputs and inputs are true balanced (either electronically or via transformers)

and

b. the equipment has proper internal Pin 1/chassis/electrical grounding layout

...you should be good to go.

One thing that helps is to have the equipment in the pre/FX rack connected to the same mains outlet as the desk/recorder via the minumum number of plugs/sockets/adaptors etc. The mains wiring should be adequately rated (to ensure a good earth connection) and use high quality signal cable.

You can also bond the metal rack chassis to mains earth using a 6mm cable to help screening and for electrical safety (this also applies to other metal outboard racks)

I find it best to keep all mic tie-lines direct without any shield/pin 1 grouping at the bay, as it ensures the phantom power return to the pre is direct.

Mark
 
Mark Burnley said:
Hi Paul,

In this application you're effectively using it as an "isolated" patch- i.e. with XLR chassis plugs/sockets Pin 1 is connected only through the plug/socket itself and doen't actually touch the metal chassis of the patch panel (as long as the plugs/sockets you use as patch leads don't have pin 1 linked to the shell)

This is the same as plugging an XLR cord directly into the equipment and sending it to the following piece of equipment.

Providing-

a. the outputs and inputs are true balanced (either electronically or via transformers)

and

b. the equipment has proper internal Pin 1/chassis/electrical grounding layout

...you should be good to go.

One thing that helps is to have the equipment in the pre/FX rack connected to the same mains outlet as the desk/recorder via the minumum number of plugs/sockets/adaptors etc. The mains wiring should be adequately rated (to ensure a good earth connection) and use high quality signal cable.

You can also bond the metal rack chassis to mains earth using a 6mm cable to help screening and for electrical safety (this also applies to other metal outboard racks)

I find it best to keep all mic tie-lines direct without any shield/pin 1 grouping at the bay, as it ensures the phantom power return to the pre is direct.

Mark
Hi Mark.  Thanks for the reply.  I wondered about that.  The FX and pres will all be in the same rack and power is all from the same main.  Problem is the XLR jacks I've selected, Neutrik NC3FD-LX-BAG, are chassis ground.

http://www.markertek.com/Cables-Connectors-Adapters/Audio-Connectors/XLR-Connectors/Neutrik-USA-Inc/NC3FD-LX-BAG.xhtml

I'll have to see if I can find some that aren't.

Paul ;D

edit: Ah ha!  Simply omit the standard connection of pin one to the chassis!  See, this is why you guys are the masters.  Thanks.
 
Mark Burnley said:
Providing-

a. the outputs and inputs are true balanced (either electronically or via transformers)

and

b. the equipment has proper internal Pin 1/chassis/electrical grounding layout

What does this have to do with wiring a patchbay?
 
gridcurrent said:
Mark Burnley said:
Providing-

a. the outputs and inputs are true balanced (either electronically or via transformers)

and

b. the equipment has proper internal Pin 1/chassis/electrical grounding layout

What does this have to do with wiring a patchbay?

Everything or nothing...  Depending on your grounding scheme, amongst other things.

What I think he is trying to say is that no more refinement of the scheme is required if those conditions hold true. This is referring to the FX I/O portion, not the Mic patching. The Mic patching will be the same as stringing three Mic cables together to connect the Mic and Pre.

 
wtmnmf said:
Everything or nothing...  Depending on your grounding scheme, amongst other things.

What I think he is trying to say is that no more refinement of the scheme is required if those conditions hold true. This is referring to the FX I/O portion, not the Mic patching. The Mic patching will be the same as stringing three Mic cables together to connect the Mic and Pre.
Now that may be a problem then.  MY FX are unbalanced.

Paul ;D
 

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