Patchbay grounding

[Winetree]

I have 24 mic lines wired into a TT patchybay. These jacks are normalled to the inputs of 500 racks.
The mic jacks have a bus wire soldered across all 24 mic shields. When patching a mic into a preamp in the 500 rack,
I'm also patching in all 24 mic shields. Should I separate the mic jack shields?

 

[fazer]

If I understand correctly , you will need shield for phantom power.  Solder the  wire  shield  to the jack.  You should not put a buss bar across the ground of the patchbay jacks.  They should each be separate from jack ground to 500 rack mic in ground/shield pin 1.  You create a possible ground loop by a buss on the grounds of the bay jacks.  There is already a buss on the 500 rack pin1 mic inputs to the backplane . 

 

[joaquins]

  Too many ssss in bussssss, one would do!

  I agree with the approach, when in doubt let the end devices do whatever they want with the shields, just route it as another signal. When in trouble start to think, if you have, for some reason, any trouble with the grounding special attention to those problematic devices could be taken, till then route the shields as another signals.

  Some studios make a star grounding at the patchbay, for the all shields. That's fine while routing all balanced gear, they don't need the shield connected. When you add to the soup mics and unbalanced gear special attention should be taken, mics need the shield for phantom from mic pre to the mic (and shielding but that doesn't need to get to the mic pre) and unbalanced needs a reference usually done by the shield, so there's no easy way to make the same connection as the others and still avoid ground loops.

JS

 

[fazer]

I know, use the word buss for bus,  go to jail. Thats the law and its a good one.
Especially around GroupDIY.  I can't believe I did that. 

 

[Winetree]

Thanks guys. The patchbay already had the shield  bus wire soldered in place. So I left it.
Everything connected to the patchbay is balanced.
I'm going to remove the bus wire and let the individual shields connect to each other.

 

[joaquins]

If the ground bus is in place and you have no loop trouble, your balanced gear may not have the shield connected on the other side, look closer (the other end of the wires) before just removing the bus.

JS

 

[fazer]

I disagree about keeping a bus wire on a mic level patchbay.  The idea of a ground plane on line level patch points keep the patch cord from popping when the tip touches the jack ground while being patch in.  The line level inputs are at a much higher level and used constantly to rearrange signal flow in a traditional analog console.  However,  65 db of gain on a ribbon microphone  can bring up the noise floor produced by a product such as a REDD DI with a power suppy , when used on a different channel.  Now the ground plane (bus wire) is contaminated by noise in the supply and carried to all mic inputs.   

For that reason I always separate the grounds on a mic bay.  I never use a bus wire on the jacks.    IMHO is to fix that issue now rather than later.  You may get by with it until something changes and then you will be forced to undo the bays and rewire and create other issues in the process. 

On my API , the line level patchbay is on a metal plate for all jacks so the shield of the console case also grabs the ground of all the jacks.  The API case has a Technical ground on the case which will go to the tech ground for the audio, i.e. ground rod.    There is no mic bay on that line level patch bay .  I added an ADC TRS 1/4 inch bay to the mic inputs on a DL connector.  That patchbay has separated jacks with shields that tie through the upper mic output jack full normal to to the lower mic input jack.  A shield from mic input is connected to the upper mic output jack so phantom power is transferred to the mic input on the panels located in the studio for drum inputs and all mic and di's feeding those inputs.

I advise you fix that now not wait for a problem on mic level bay.  On all line level jacks I would use bus wires and address one by one on opposing ends to elimate ground loops . 

 

[JohnRoberts]

The last time I put a patch bay inside a console we were not as well informed about pin 1 corruption as now.

The safest way is to telescope all 3 contacts through the patch points using the switched normalled contacts so the sending and receiving circuits just see a longer wire.  (caveat I haven't done this since a few decades ago). Multiple ground connections can introduce shield current flows and voltage drops.  Alternately you could make the patch bay ground zero for the console mic inputs, while best practice is to ground shields to the nearest solid chassis ground.

In theory a well designed and executed mic preamp should not worry about bused shield grounds, but do you feel lucky?  If using older legacy gear in combination with new stuff I would consider the safer approach.

JR

 

[SSLtech]

I've made and installed many patchbays, and my "standard" rules -distilled after many years- are as follows:

Line level signals:
Buss all grounds at patchbay.  (In case of truculent gear grounding issues, since all other equipment uses scattered versions of grounding, make the fix at the OTHER end ... otherwise there is NO consistency!)

Mic level signals:
Isolate all rounds from patchbay rack metal ground.  "strap" grounds vertically, or -if you want to be *extremely* persnickerty- use normalled ground contacts also, and  normal vertically also.

Whatever you do, you will still run the chance of encountering ground issues if and when you plug in a locally-powered device, such as a tube microphone... Have a handful of short ground-lifted XLR cables to use if this brings hum into your life. MARK THEM CLEARLY.

 

[mattiasNYC]

I've made and installed many patchbays,

Sorry for this off-topic: I tried to PM you a while back but couldn't get through since your PM-box was full or something. Would you mind cleaning it? Just have a question to ask you...

 

[JohnRoberts]

I've made and installed many patchbays, and my "standard" rules -distilled after many years- are as follows:

Line level signals:
Buss all grounds at patchbay.  (In case of truculent gear grounding issues, since all other equipment uses scattered versions of grounding, make the fix at the OTHER end ... otherwise there is NO consistency!)

amen.....    but I would bus the grounds not kiss them. 

Great for a fixed installation or studio  where you have the luxury of time to sort out pin one problems. For situations where you must interface with odd customer's gear (either the customers, the gear, or both), and can't say no, and inputs are not co-located with the patch bay consider telescoping the grounds thru.

You can experiment, and nobody says all patch points must be the wired the same.

Mic level signals:
Isolate all rounds from patchbay rack metal ground.  "strap" grounds vertically, or -if you want to be *extremely* persnickerty- use normalled ground contacts also, and  normal vertically also.

Whatever you do, you will still run the chance of encountering ground issues if and when you plug in a locally-powered device, such as a tube microphone... Have a handful of short ground-lifted XLR cables to use if this brings hum into your life. MARK THEM CLEARLY.

Merry Christmas, seasons greeting, and happy festivus stranger, I hope you and yours are well. Still riding your bike?

JR

 

[Bob]

Keef, aka Keith,
Please give us (ME) a way to reach you. Your "IN" box is full and not accepting new messages.
I need your help with an SSL console and a few other things.
Thanks
Cajun Bob aka [email protected]

 

[JohnRoberts]

Keef, aka Keith,
Please give us (ME) a way to reach you. Your "IN" box is full and not accepting new messages.
I need your help with an SSL console and a few other things.
Thanks
Cajun Bob aka [email protected]

odd that you post to a 2016 thread when he has been active within the last month.

maybe ask here https://groupdiy.com/index.php?topic=70128.msg894749#msg894749

JR