How to upgrade patchbay without ground loops
« on: July 03, 2019, 08:29:15 PM »
Hey fellas,

I'm in the process of upgrading the patchbays on my Sound Workshop Series 40 console to Switchcraft. I've figured out which wires correspond to what i/o, but I'm not sure how to wire the grounds on the new patchbay.

With the stock implementation, the ground wire on some cables coming from the console is not used, and instead the ground is provided via the patchbay itself, yet on other connections (line in, patch out) all 3 wires are used, including the ground wire coming from the console. The question then becomes, do I wire the new patchbays in this same manner, with the grounds "passed through" from the console on some connections (ie. line in, patch out)...while on others (ie. bus out, dir out, patch in) ground is provided via normalling from other connections? Or should I use all 3 wires coming from the console on all connections?

I want to make sure I'm not creating ground loops anywhere. The studio will be using star chassis ground scheme. I've made a short video to demonstrate exactly what I'm talking about in case it might be helpful: https://www.youtube.com/watch?v=IziyiVGM5E0

Thanks very much!!

Jonny


Winetree

Re: How to upgrade patchbay without ground loops
« Reply #1 on: July 03, 2019, 10:26:14 PM »
One grounding scheme is to only connect the ground or shield on the sending end.
Thus a return would not have the shield connected on it's end.
Use the same grounding scheme.
Also the stock patchbay probably has some normals or half normals.

PRR

Re: How to upgrade patchbay without ground loops
« Reply #2 on: July 03, 2019, 10:55:23 PM »
> do I wire the new patchbays in this same manner

Do you figure you know better than the folks who built it? Then do it your way. Otherwise, put your brain in Park and just copy what they did.

> "passed through" from the console on some connections (ie. line in, patch out)...while on others (ie. bus out, dir out, patch in) ground is provided via normalling from other connections?

Logically, lines that run from AND to console share a ground in the console and should not take-up a different ground in the jackfield. OTOH a "line input" may come from the 13th floor or even across town, and should pick-up ground where it comes to the jackfield. It may not be that simple. But there is probably a reason they did it different for different classes of links.

abbey road d enfer

Re: How to upgrade patchbay without ground loops
« Reply #3 on: July 03, 2019, 11:20:46 PM »
I have a feeling the particular wiring has been done for practical reasons; probably 15 pin connectors were not usable, may be too big, or not available, or ...?
The designer probably considered that connecting the console ground via two shields (for redundency) was adequate.
Since you're hard_wiring, I would think one single good connection is better than two mediocre.
I don't see any potential for creating a "ground loop".
I suppose you have checked all the connections, and all the shields are actually tied to the same console "ground".
The final decision is yours; is it more practical to wire them all point-to-point (3-wire) or bus the "grounds" across the patchbay and wire the lines "floating" ? IMO the issue is not a technical one.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

squarewave

Re: How to upgrade patchbay without ground loops
« Reply #4 on: July 04, 2019, 01:25:28 AM »
It's not uncommon to wire all of the grounds on a patchbay together. If you look carefully at the standard metal solder lug style bantam / tt jacks, you'll see that the ground lug has a funny off-axis "hole" so that you can just run a single piece of buss wire across multiple jacks.

Note that this would not create ground loops because the shield ground is not (or should not) be used as a signal reference. Even if the source or destination is unbalanced, it uses pin 3 as analog 0V reference. Yeah, technically connecting all the patchbay ground / pin 1's together will make lots of loops but you shouldn't care because they're just shields.

Although for some reason I always wired patchbays with "pass through" ground. I guess I just never saw a reason to connect all of the shields together.


 

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