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Mic patchbay grounding schemes
Old 7th November 2011
  #1
Gear Head
 
🎧 10 years
Mic patchbay grounding schemes

Hello,

We are in the process of adding a TT mic patchbay to our studio.

We are gonna be using a solder type switchcraft patchbay.

The first bank of 24 (upper row) is gonna be the mic lines coming from the live room studio box. these are gonna be fully normalled to the bottom row ( console mic ins)

second bank of 24 is gonna be external mic pre line outs ( upper row) and external mic pre mic inputs ( bottom row). no normalling obviously.


This is our predicament.


there are two ways to provide phantom power to the normalled mic lines in the studio ( without inserting a TT cable)

1. build a dedicated phantom studio box. best idea, but a future idea as well.

2. vertically strap the grounds in the first bank with small cables. this works, but i have a question. when you insert a plug ( and therefore break the normal), the vertically strapped ground is not broken. Suppose you route that signal to an external mic pre. In that case, the signal will be presented with 2 ground paths. The one from the vertically strapped ground (that is not broken), and the one from the TT cable going to the external mic pre. Is this problematic? Could it be? Is it best that we find another patch with ground normalling as well?


I found this explanation of a patchbay type in another thread :

4. Switched Ground - "Each vertical pair of audio circuits has shields common and is isolated from the front panel and adjacent circuits. Inserting a plug lifts shield."


We tested it at the studio with another patchbay an there was no problem. But before we go on and solder everything i want to cover all bases!

Any experience is greatly appreciated.


Thanks,

Alex
Old 7th November 2011
  #2
Lives for gear
 
🎧 10 years
Patchbays
Old 7th November 2011 | Show parent
  #3
Gear Head
 
🎧 10 years
Hey Bill,

thanks for your reply.

We are not gonna be using an xlr patchbay for various reasons.

Does someone have experience with the specific scenario i described? Its not that uncommon, and ground normalling patchbays are kinda rare.


alex
Old 8th November 2011 | Show parent
  #4
Gear Maniac
 
radeng's Avatar
 
🎧 10 years
Quote:
Originally Posted by Phase Shift ➑️

We are not gonna be using an xlr patchbay for various reasons.

You really ought to rethink this. A 1/4" bay for mic level is a bad idea, TT even more so.

I have been building audio control rooms for over 30 years. I design them so less skilled operators can use the patchbay without risking blowing things up. Ignore this advice at your peril.
Old 8th November 2011 | Show parent
  #5
Gear Head
 
🎧 10 years
hey rad eng.I am guessing you are reffering to phantom power issues right? How about LFACs that usually have mic level patchbays ?


In the mean time,do you have any idea regarding my initial enquiry?

thanks a lot

alex
Old 8th November 2011 | Show parent
  #6
Gear Nut
 
🎧 10 years
Quote:
Originally Posted by radeng ➑️

You really ought to rethink this. A 1/4" bay for mic level is a bad idea, TT even more so.

I have been building audio control rooms for over 30 years. I design them so less skilled operators can use the patchbay without risking blowing things up. Ignore this advice at your peril.
Complete total agreement. And not just because of Phantom power. Look at how the plugs and jacks make contact. You end up with a tiny point contact. As it ages, it stops working. They worked in the telephone industry because of high currents and high voltages. Some people keep them working with regular maintenance and I mean regular, but leave them alone and they will go noisy and or open. Microphone level signals, use XLRs.

Been there, done that, have the scrap pile to prove it.

Frank
Old 8th November 2011 | Show parent
  #7
Lives for gear
 
gyraf's Avatar
 
🎧 15 years
And then again - our Calrec and SSL desks never had issues with this, more than the regular need for cleaning that affects line-levels too.

Main problem is users throwing phantom power back into electronically balanced outputs, blowing capacitors and output drivers.

As for grounding schemes - why not trust your console manufacturer's original scheme and terminate each individual micline at the desk XLR input?

Jakob E.
Old 8th November 2011 | Show parent
  #8
Gear Head
 
🎧 10 years
Quote:
Originally Posted by gyraf ➑️

As for grounding schemes - why not trust your console manufacturer's original scheme and terminate each individual micline at the desk XLR input?

Jakob E.

Hey jacob,

We are gonna do just that. But we have to normal the grounds as well from top to bottom row so that the console mic pres are able to pass phantom when needed. My question is this though, when patching to an external mic pre, this ground normallin will not be broken like the tip and ring normals. Is this able to generate hum or the like since there will be 2 paths to ground? ( the one from the console mic line ehich will not be broken, and the one from the external mic pre via the patch cable)

regarding the XLR patchbay. Is there a way to construct one with normalling, or do i have to have 24 xlr patch cables connected at all times?

alex
Old 9th November 2011 | Show parent
  #9
Gear Maniac
 
radeng's Avatar
 
🎧 10 years
No such animal as a xlr bay with normalling. Yes you have to use a bunch of short xlr patch cords.

Although-

You could have switches for each of your mic inputs to pre-select different input jacks around the studio, i.e. Panel A, Panel B, etc...

If you have a lot of extra cash, you could even put a mic level router in front of your console inputs. That would be the ultimate in convenience, but the most expensive.

Jakob,

The examples you cite are from very high end consoles that are likely to be operated by experienced engineers. For the average studio with average users, mic level on anything but a XLR bay is a disaster waiting to happen.
Old 10th November 2011 | Show parent
  #10
Gear Head
 
🎧 10 years
Well, while i wouldnt call or studio "top of the high end" its not bad either.Certainly not average. And we are certainly not average users. I cant for the life of me understand how you made that deduction.

regardless, does anyone have an answer on the specific question about the grounding?

alex
Old 10th November 2011 | Show parent
  #11
Gear Maniac
 
radeng's Avatar
 
🎧 10 years
Sorry Alex, no slight to your studio or people, only your patchbay plan.

John

PS. Use external phantom if you insist on your plan.
Old 11th November 2011 | Show parent
  #12
Gear Head
 
🎧 10 years
Yes, building a studio box with phantom power capability and illuminated switches is a very promising concept. Do you happen to know a dedicated 48 v power supply with enough mA to power say, 24-32 channels of active devices?



alex
Old 11th November 2011 | Show parent
  #13
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by Phase Shift ➑️
Well, while i wouldnt call or studio "top of the high end" its not bad either.Certainly not average. And we are certainly not average users. I cant for the life of me understand how you made that deduction.

regardless, does anyone have an answer on the specific question about the grounding?

alex
One: I would NEVER tie ANY grounds together on Mic level patching...The grounds are made ONLY via the grounds (Shield) of the Patch cables...

Two: My first preference for Mic Level is XLR.. 2nd Preference would be the 1/4" Longframe, 4th; TT.. And No I did NOT forget 3rd...
Old 11th November 2011 | Show parent
  #14
Gear Head
 
🎧 10 years
Quote:
Originally Posted by nosebleedaudio ➑️
One: I would NEVER tie ANY grounds together on Mic level patching...The grounds are made ONLY via the grounds (Shield) of the Patch cables...

Two: My first preference for Mic Level is XLR.. 2nd Preference would be the 1/4" Longframe, 4th; TT.. And No I did NOT forget 3rd...
well if we dont tie vertical grounds( shields, pin 1) together then the console will not be able to power 48v devices , unless there is a patch cable inserted from top row to bottom row. which makes the whole concept of normalling moot. is there any other workaround except patchbays with ground normalling and XLR bays?
Old 11th November 2011 | Show parent
  #15
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
The way I normally wire a studio is I will have 2 Mic lines(XLR) per Mic Panel per small room back to the CTR, larger rooms 4-8 Mic lines, this works well99% of the time for outboard Pres, adding more is No big deal..
Then ALL Mic Pres Ins go to another XLR Panel with the Mic Lines from each room...Patching via Short XLR cables, this also allows Mic patching in the CTR VERY easy..

Yes the down size is Size of the panels...But the results are Superior IMHO..
I have YET to see a BAD XLR connector..Not the Good ones that is, have seen MANY bad/eratic 1/4" connectors..Over the past 35+ Years...
And I clean XLR's when I think of it...
Old 11th November 2011 | Show parent
  #16
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by Phase Shift ➑️
well if we dont tie vertical grounds( shields, pin 1) together then the console will not be able to power 48v devices , unless there is a patch cable inserted from top row to bottom row. which makes the whole concept of normalling moot. is there any other workaround except patchbays with ground normalling and XLR bays?
I Don't like mic lines normalled either way...
This is up to you...
My method is those Special XLR's are ONLY connected when a Patch cable is inserted..
This is also used when a Console is in place, using the console Pres...
Old 11th November 2011 | Show parent
  #17
Gear Head
 
🎧 10 years
meaning at least 24 xlr to xlr patch cables connected at all times , unless you want to use another preamp. then another TT patchbay with the external mic pre line outs ( we are out of tie lines in the console patchbay) Much more expensive solution, although admittedly "idiot proof".


alex
Old 11th November 2011 | Show parent
  #18
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by Phase Shift ➑️
meaning at least 24 xlr to xlr patch cables connected at all times , unless you want to use another preamp. then another TT patchbay with the external mic pre line outs ( we are out of tie lines in the console patchbay) Much more expensive solution, although admittedly "idiot proof".


alex
Well, unless I was there and could see the set up some of this is meaningless...
Old 11th November 2011 | Show parent
  #19
Gear Head
 
🎧 10 years
i am more interested in the implications of grounding than the routing and overall scheme. i got this figured out.

Just to give you an overall view though, we have a 34 channel LFAC and 18 channels of outboard pres. My goal is to have the first 24 channels of the console normalled from the mic lines in the main room, and be able to swap any external mic pre in any of those 24 inputs. the way we did it so far was having a dedicated studio box for all the external mic pres. If you wanted to swap pres, you'd have to go in the live room.

All this in XLR format is many U ... and money.

alex
Old 11th November 2011 | Show parent
  #20
Gear Guru
 
Musiclab's Avatar
Quote:
Originally Posted by Phase Shift ➑️
Hey jacob,

We are gonna do just that. But we have to normal the grounds as well from top to bottom row so that the console mic pres are able to pass phantom when needed. My question is this though, when patching to an external mic pre, this ground normallin will not be broken like the tip and ring normals. Is this able to generate hum or the like since there will be 2 paths to ground? ( the one from the console mic line ehich will not be broken, and the one from the external mic pre via the patch cable)

regarding the XLR patchbay. Is there a way to construct one with normalling, or do i have to have 24 xlr patch cables connected at all times?

alex
Do I have this right, you want to normal specific mic panel outputs to pre amp in's. or your consoles mic pre ins?
As far as using a tt bay for mic panel out's to mic pre in's I used a 1/4 balanced bay for a while, I got tired of having to turn the phantom off wait a second for the phantom to die out, change what needed to change and turn the phantom back on. Do yourself a favor, make a XLR patch panel
Old 11th November 2011 | Show parent
  #21
Gear Head
 
🎧 10 years
Quote:
Originally Posted by Musiclab ➑️
Do I have this right, you want to normal specific mic panel outputs to pre amp in's. or your consoles mic pre ins?
the console's mic ins. so that we have the same path we had prior to installing the patchbay.
Old 11th November 2011 | Show parent
  #22
Gear Guru
 
Musiclab's Avatar
Quote:
Originally Posted by Phase Shift ➑️
the console's mic ins. so that we have the same path we had prior to installing the patchbay.
the purpose of a mic patchbay is so you can patch in whatever mic , appearing at whatever mic panel output you want into to whatever pre you want. This usually is NOT normalled. I'd still recommend you reconsider and make an XLR bay for this
Old 11th November 2011 | Show parent
  #23
Gear Head
 
🎧 10 years
Quote:
Originally Posted by Musiclab ➑️
the purpose of a mic patchbay is so you can patch in whatever mic , appearing at whatever mic panel output you want into to whatever pre you want. This usually is NOT normalled. I'd still recommend you reconsider and make an XLR bay for this

But most LFACs that have patchbays with mic lines have normalling. I want to emulate this with an external patchbay. It saves me 24 patchcords and give a streamlined workflow where everything appears at the console mic pres, except the ones you break and send to external mic pres. Even if you wanted to cross patch the mic into different console mic pres you could.

I dont have nothing against xlr bays.But, Its gonna turn out to be too expensive and big for the kind of i/o i want.

My guess is that the best scenario is external phantom powering at the studio box and a patchbay with ground normalling as well.


alex
Old 12th November 2011 | Show parent
  #24
Gear Head
 
Travis1000's Avatar
 
🎧 10 years
I've always wired studios with TT patchbays and then wired the mic lines to the top row with them fully normalled to the console on the bottom row (just like you described). It's never caused me problems and it seems to be the norm in the studios I've been in. I've never considered your question about having ground having two paths, I see what you mean though...
Old 12th November 2011 | Show parent
  #25
Gear Guru
I also did the normalled TT mic patch points 30 odd years ago. Bad idea.

First, mic signals are very small, millivolts. The amount of corrosion and dirt picked up will make them ittermittant over time. You will find diode effects at those low levels, that adds THD. The Scotch Pad only worked on the TT plugs, bunishers and cleaners were contantly used on the TT jacks, with little long term success.

The other problem found was from phantom power. One cannot expect every guest AE to know to NOT turn on the phantom before patching mic lines. The results are sparks and possible blowing mic preamp input blocking capacitors. The reason is simple: The tip hits the sleeve before you push the TT plug all the way in, that creates a momentary 48 volt short to ground = ouch!

If you must do this, don't cheap out, go XLR. Or, find out what others are already telling you.
Old 13th November 2011 | Show parent
  #26
Gear Maniac
 
radeng's Avatar
 
🎧 10 years
Quote:
Originally Posted by Jim Williams ➑️
One cannot expect every guest AE to know to NOT turn on the phantom before patching mic lines. The results are sparks and possible blowing mic preamp input blocking capacitors.
Another significant danger is damaging the control room monitors from a chain that will pass DC. Don't laugh. I've seen woofers jammed stuck at or past their limit of excursion.

A used broadcast grade mic level router would work in place of the patchbay. You can find nice ones for pennies on the dollar these days.

A big enough 48V PSU for multi-channel phantom in your studio XLR box is not a rare item. Mouser, Digikey, etc...

Or line up some old AKG N66E 6 channel boxes. I have two and rarely need more than 12 powered inputs on a session. Just how many condensers do you need all at once?
Old 13th November 2011 | Show parent
  #27
Gear Head
 
🎧 10 years
There are some compelling arguments in all. Which instantly means +600 euro, and 7 u instead of 1 u.


Radeng, where can i find such a mic level router. Any specific brands?


Regarding the 48v, there is always the solution of rerouting the console's 48 v to the live room.Makes the most sense. And i think most condensers/di's weve used was something like 8-10. And some classical projects but i dont think weve ever used 24.. Of course, if we had a much bigger live room...

alex
Old 16th November 2011 | Show parent
  #28
Lives for gear
 
crosscutred's Avatar
 
🎧 10 years
I've got one of these

Rolls Corporation - Real Sound - Products RPB486 Phantom Hex

and one of these (E725)

EMO Systems - Phantom Power Supplies

and I find that I have never been short with 8 lines of P48 (and I do have a big live room) I could quickly and easily install some more though.

I have the outputs of these and the passive mic lines appearing at the console tt patchbay (I didn't bother with normalling, it's not much trouble to patch them)

I have a xlr panel where all the studio tie lines terminate.

I have looms that I simply plug in there for either the phantom lines or passive lines that go to the phantom boxes or the console patchbay.

I used these for the xlr panels

Patch

3 years and no dodgy connections yet (the jack sockets from there however were nothing but trouble and got swapped out for neutrik in the first year)

It's foolproof and I can patch anything anywhere.

Hope that helps
Old 16th November 2011 | Show parent
  #29
Lives for gear
 
Steamy Williams's Avatar
 
🎧 15 years
Quote:
Originally Posted by Phase Shift ➑️
My guess is that the best scenario is external phantom powering at the studio box and a patchbay with ground normalling as well.
That's what I've bought for the installation of my new console (which has hasn't happened yet). I picked up an Audio Accessories ground-normalling TT patchbay for mic level signals, and an AKG N66E 6-channel phantom power unit to go in the live room. I got both of them secondhand relatively cheaply.

However, the decision to do this was partly based on the fact that outside engineers rarely, if ever, run sessions at my studio. I'm always either engineering, or at the very least assisting.
Old 2nd August 2017
  #30
Gear Nut
 
SunkenCity's Avatar
It's a little frustrating when people ask a pretty specfic question about something and the whole thread gets derailed and people keep restating the same thing over and over again.

Disregard that its a mic line with or without phantom lets just say it's line level inserts.

What happens if a two tt points are normalled together and vertically strapped to each others shell and then you patch into a pre input that doesnt have its shell lifted?

Ground loop? Should the pre input always have the ground lifted?
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