Is this the "Correct" wiring Diagram?? at DVinfo.net

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Old July 25th, 2005, 02:19 PM   #1
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Is this the "Correct" wiring Diagram??

Quoted from a web search for proper connections for XLR
Quote:
If the cable is to be used for microphone or non mains powered musical instrument connections, i.e. with low (non line level) signals, the cable shield should also be linked to the signal sending side connector’s ground pin.

There are two reasons for this:
To extend the shielding function to the microphone or instrument’s housing.
And also with phantom powered condenser microphones:
To provide a phantom power supply current return path.

In all other cases (i.e. line level connections) leaving the cable shield disconnected at one side of the cable (drawn above) is safe practice. This to avoid ground loops with non properly internally grounded equipment.

If with these “one side disconnected shield” connections RF interference problems are experienced, reconnecting the shield at the side where it was disconnected by means of a series network of a 47 Ohm resistor and a 10 nanoFarad ceramic disc capacitor is advised. Latter may be standardly applied for all balanced line level interconnections.
My question is what is the most preferred and safest method - would the 47ohm resistor and 10nanofarad cap network be the preferred and safest way to make-up cables??

I need to make up some cables since the dweebs around here in my town don't know squat of what I'm talking about. Cables required are mic cables and line cables from sound boards

Many thanks

Cheers
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Old July 26th, 2005, 08:08 AM   #2
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If the equipment in your system is working correctly and properly wired together, there shouldn't be any need for the additional work for adding the RF protection unless you're in an extremely harsh RF environment. And then probably for only a few of your cables.
I would simply use a high-quality Star-Quad type cable like that made by Canare and high-quality XLR connectors like those from Neutrik.
If you wire them in the correct manner for StarQuad cable, you shouldn't have any problems and all your cables would be interchangeable for any use.
If you have a problem after that you could trace it and take care of it.
(Personally, I buy my cables already constructed from a company I trust. It saves me a lot of time and their cost is reasonable.)
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Old July 26th, 2005, 09:52 AM   #3
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Here's how I've always made/repaired XLR cables: pin1=ground (shield), pin2=hot (usually red), pin3=cold (usually black). I've never encountered the RF network mentioned above.

I suppose an easy way to do this, should the situation require, would be to make a short 6" adapter cable with the resistor and capacitor in place. I've also heard of making "ground lift" cables of this sort (only pins 2 & 3 feed through). Sometimes they even break out the ground wire from pin1 to a chassis ground instead of going through the input ground to avoid the internal circuit board. This is still only in extreme cases. (Granted, there are some sound systems that are extremely messed up out there.)

Note that the ground wire will always be required for phantom powered mics.
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Old July 29th, 2005, 04:22 PM   #4
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You can also buy ground-lift XLR plug-on adapters. Keep a couple on hand in case you ever need them (very occasionally, you might), but otherwise connect both ends of the shield on all your cables.

Standardization is a good thing.
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Old July 29th, 2005, 08:28 PM   #5
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I used to think that until I met with someone who does live sound. Apparently thee are some issues with connected shells in live sound that can be a problem.

Ty Ford
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Old July 30th, 2005, 06:30 AM   #6
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When the shield is tied to the connector body and more than one cord is plugged into a stage box or snake box it can tie all of the shields together at a point other than the mixer input. In the case of wall plates and stage boxes it can also tie the shield to the conduit system. This can cause hum and buzz problems.

Sam
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Old July 30th, 2005, 07:23 AM   #7
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Quote:
Originally Posted by Sam Gates
When the shield is tied to the connector body and more than one cord is plugged into a stage box or snake box it can tie all of the shields together at a point other than the mixer input. In the case of wall plates and stage boxes it can also tie the shield to the conduit system. This can cause hum and buzz problems.

Sam
Guys

Many thanks all for the advice.

The way I read these posts and the conclusion I draw from them are the following:
1. Don't tie the shield to the body of the connector
2. Have cables where the shield is tied through and ground-lift XLR plug-on adapters to avoid problems

A question I have is this, is there anyhere on the net where one can find the CORRECT connections to make up these ground-lift XLR plug-on adapters and cables. The local company who supplies cables do straight connections and when I mentioned "ground-lift XLR plug-on adapters" and "ground lift cables" all I got was a puzzled stare!! These guys don't know what I'm talking about!!

Hell, wish I was in the States where these things are readily available. I have purchased high quality cable and a smattering of different connector types and would rather make up my own cables then I know I'm right!

Any help here would be appreciated.

Cheers
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Old July 30th, 2005, 08:51 AM   #8
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I'd say, if you're only going to use the cables in your (properly constructed) studio and you have fear of RF, tie the grounds to the ground pin and the shell at each end.

A buzz in the line COULD mean a nasty shock for the performer if he or she gets in between some bad potential differences. Worst case it could kill them. Best case, a mild tingle.



Ty Ford
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Old July 30th, 2005, 10:55 AM   #9
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For information on how to connect anything to anything (well almost) try this site http://www.rane.com/library.html . Look for Sound System Interconnection (Rane Note 110). It's about 2/3 down the page.

Sam
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Old July 30th, 2005, 01:19 PM   #10
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Quote:
Originally Posted by Sam Gates
For information on how to connect anything to anything (well almost) try this site http://www.rane.com/library.html . Look for Sound System Interconnection (Rane Note 110). It's about 2/3 down the page.

Sam
Ah Sam you beauty!!!!!!!!!

This was exactly what I was looking for - Chris, we should make this a sticky!

Ty, this is actually my problem. Most times I am NOT in a (properly constructed) studio and want to cover myself for most eventualities hence my wanting to make up cables and adapters for most eventualities. Can't do it all but am looking to cover my bases as best as possible.

Sam's post has helped immensely and offers a variety and some sound advice (pardon the pun).

Cheers
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Old July 30th, 2005, 03:45 PM   #11
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Glad I could help.

Sam
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Old August 1st, 2005, 11:12 AM   #12
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Quote:
Originally Posted by Ty Ford
I used to think that until I met with someone who does live sound. Apparently thee are some issues with connected shells in live sound that can be a problem.

Ty Ford
Not sure if this was in reference to my post, but I wasn't suggesting connecting the shield to the XLR shell, just to pin 1.

-Troy
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