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 Forum index » How-tos » Production - engineering/mixing
Studio wiring - duplicate grounding wires connecting devices
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williamsharkey



Joined: Jul 31, 2005
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PostPosted: Sat Feb 13, 2010 11:15 pm    Post subject: Studio wiring - duplicate grounding wires connecting devices
Subject description: Good or bad thing to have duplicate ground wires connecting gear?
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I am wiring a patch bay to connect the outputs of one sound card to the inputs of a second sound card. Also, I will be connecting a good amount of my gear to this patch bay.

The patch bay came used, I am taking the connections apart and re-doing them. I noticed something interesting. The ground pins(or whatever they are called) were wired together. This seems like a good idea, I will do this when I re wire.

To connect the sound cards to the patch bay, I am using cable that the patch bay came with, and soldering on TRS connectors. In the end, I might make up to 16 connections to each sound card.

The cable I am using has three conductors in it, one for tip, one for sleeve and one for ring. Should I only wire one ground from the patch bay to sound card, or should I connect every one - in each cable?

Having duplicate ground connections will be like having a bunch of antennas, right? Perhaps raise noise?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Left is a diagram of only connecting one ground to patch bay. Right is a diagram of connecting all of them.

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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Antimon



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PostPosted: Mon Feb 15, 2010 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

I remember when I bought my cheapo patchbay, the salesman told me I could benefit from using balanced cables, but a single unbalanced connection would ruin whatever good all the balanced cables did. I didn't really know at the time what balancing did... I know a bit more now, but I'm still confused by that statement. Would love to see an insightful response to the first post here!

/Stefan

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EdisonRex
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PostPosted: Tue Feb 16, 2010 4:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I wish there was an option where you get to say both of the diagrams are wrong. The object is for there to be a single path to ground/earth from any given point. More than one path and you're more likely to have loops (not that you will have loops, but it is more likely).

So the first diagram has issues with multiple paths in the middle, by the look of things. The issue arises with the ground paths of the cables you're then plugging into it. The bit in the middle, well, as far as I can tell has a fundamental problem of tying the earthing across the normals. I think that is likely to cause problems.

Likewise the 2nd option, doesn't fix the multiple paths problem. In fact it enhances it. Again, the cross ties in each patchbay are the source of the problem. Isolating earths throughout the patchbay is acceptable, albeit more complex, but you have to make sure you're actually able to isolate them.

And why isolate each patchbay jack? Again the issue is multiple ground paths. Now Antimon brings up an interesting side issue, mixing balanced and unbalanced connections in an electrically common patchbay and what that does.

The idea of balancing is to isolate the signal components from any RF or electromagnetic interference, by causing any injected noise to cancel itself out. This is discussed elsewhere in the forums and I won't go too much into that now. The allusion to "ruining" whatever good you get from balancing by injecting an unbalanced hi impedance signal into it is only based on the likelihood of higher noise superimposing itself into the balanced signal sets via the ground, which gets harder to completely reject as it adds up.

If you ever build a stage box/snake (the traditional kind as opposed to the modern fiber technology ones) each signal pair is shielded and the best ones don't have any common earths in the box. Single path to the reference point. Multiple paths to reference point mean multiple reference points, potentially speaking.

Anyway, single point of reference for ground is good. This is why ground lifters work, and why some purists don't connect the shields on one end of their patch cables. So think about that when you look at those diagrams.

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