Patchbay Question - Where to connect ground wire?

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wing
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Patchbay Question - Where to connect ground wire?

Post by wing » Fri Oct 05, 2018 9:22 am

Hi there, sorry for the somewhat noob-like question... But I bought a pre-wired balanced TRS patchbay with snake off eBay awhile back and it came with no documentation. The basic wiring part was easy though, I'm familiar with all that. But there is this little green wire connected to the chassis with a metal hook on it, which I assume is a ground wire that I need to connect to the ground. But it's kind of short– only about 1-2 feet. So at first I thought maybe it just needs to connect to something metal? So I was assuming it has to sit on the screw that tightens the bay into the rack. But that didn't seem to work well, and I'm getting some noise/interference on the channels, which I assume means this thing isn't grounded correctly.

So then my next assumption is that maybe it needs to sit over the actual ground pin on whatever 3-prong plug I have the rest of my equipment plugged into. However, the nearest outlet where everything is plugged into is about six feet away, so there is no way this ground wire would fit. So would I then need to get a longer ground wire and resolder that to that chassis?

Or is it some other thing that I'm not thinking of altogether? I searched all over Google but can't seem to find much information on what to do with this wire. Thanks for looking!

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Re: Patchbay Question - Where to connect ground wire?

Post by floid » Fri Oct 05, 2018 1:05 pm

Is there continuity between all sleeves/ pins 1 on your wiring harness?
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Re: Patchbay Question - Where to connect ground wire?

Post by wing » Sat Oct 06, 2018 5:59 am

floid wrote:
Fri Oct 05, 2018 1:05 pm
Is there continuity between all sleeves/ pins 1 on your wiring harness?
Hi, I checked and yes it runs all the way through every patch point on pins 1...

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Re: Patchbay Question - Where to connect ground wire?

Post by floid » Sun Oct 07, 2018 7:41 am

I suspect a ground loop issue. Sounds like the patchbay is probably intended to be used as the star ground point for all shields of all balanced signals it carries. A shield only has to be connected to ground at one point to do its job. Connecting at multiple points can introduce these problems.
You might try a systematic approach to finding the simplest set of connections to the patchbay that is hum free, and then adding one device at a time until the hum appears. Then see if lifting the shield ground eliminates the hum.
I set my patchbay up so that all input connector shields are connected, and all output connector shields are floating.
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Re: Patchbay Question - Where to connect ground wire?

Post by Nick Sevilla » Sun Oct 07, 2018 7:15 pm

Hi,

Unless you have a lot of unbalanced / funky / ancient equipment, you will not be needing this ground wire.

Also, this type of grounding scheme is mainly used in old recording studios, where the console was connected
to this type of patchbay, and an actual technical engineer was responsible for making sure it did not make noise.

So, you need to understand what these things are first:

1. Star configuration grounding scheme. This is a type of ground wiring scheme, where there is ONLY one point at which ONE wire touches GROUND. Every piece of equipment "floats" their own internal ground, and uses the one through the patchbay, for their audio signal. This is useful for older and newer equipment when connected together. MOST modern equipment (les than 15 years old or so), uses a different grounding scheme where their audio and power grounds are separated, or isolated. So those do not need this sort of patchbay.

2. Ground potential. Depending on the equipment, different gauge wire and also different way of getting to ground are used. Which causes some equipment to "go faster to ground" than others. This is what causes a lot of hum problems in studios. Some equipment hold a small charge, which then causes hum. Thus this type of patchbay, where all the grounds come here and get dealt with.

Depending on your studio configuration, you pay have to either keep this patchbay as is (how are your other patchbays?) or you may have to go through it an remove the entire ground wire, thus making it a regular, non star ground patchbay.

Cheers
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