Drain Wire-Multipair Audio Cable

[ckvox]

I'm wiring connectors onto a Gepco 12-pair snake. I know that the individual shields for each pair get wired to the appropriate pins on the connectors.

However, there's a separate drain wire and foil shield that runs along the inside of the outer jacket of the snake. Does this drain wire get hooked to something and, if so, what?

Thanks.

[DrFrankencopter]

I would connect one side of that drain wire to your patchbay earth, or wherever your other chassis grounds return to. Leave the other side floating.

Cheers

Kris

[ckvox]

Originally Posted by DrFrankencopter

I would connect one side of that drain wire to your patchbay earth, or wherever your other chassis grounds return to. Leave the other side floating.

Cheers

Kris

Hey Kris. Not really sure about "patchbay earths" and "chassis grounds." Here's what I have: Connectors on one end of the snake will be going into a Digidesign 003 Mixer. The other end will be going into a custom jack panel attached to the side of my vocal booth. What do you think?

Thanks!

[DrFrankencopter]

Typically the drain wire returns back to the AC outlet ground pin.

The chassis of your mixer should also attach to this ground (assuming it is metal/conductive) as both a shielding element, and a safety element (protecting you from a short circuit to the case).

I'm not sure how best you can do this for your installation. It's pretty easy if you are using a patchbay since the AC ground (earth) is brought out to the bay. If there is an outlet nearby the wall wall panel in your booth you might be able to tie a wire from its ground over to your panel...but I would only do this if you're still in the construction phase of your booth. Leave the other end of the drain wire disconnected.

Cheers

Kris

[jhbrandt]

Sorry, but I disagree strongly. Do not run a ground wire from an outlet & definitely hook the drain wire on both ends of the cables to the earth pin of the connector. I'll write more tomorrow.
John

Sent from my GT-S5830 using Gearslutz.com

[ckvox]

Originally Posted by jhbrandt

Sorry, but I disagree strongly. Do not run a ground wire from an outlet & definitely hook the drain wire on both ends of the cables to the earth pin of the connector. I'll write more tomorrow.
John

Sent from my GT-S5830 using Gearslutz.com

Hey John. Just to make sure we're all on the same page here, I am, of course, hooking both ends of the shield for each individual pair to the ground pin on its respective connectors (XLR's mostly and a few TRS). That part I understand.

What I'm talking about is the "overall" drain wire that's just inside the outer sleeve of this Gepco multi-pair cable (GA72412GFC). I'm just trying to figure out what, if anything, I'm supposed to do with that specific drain wire.

Thanks!

[ritelec]

did a search..........not knowing..........curious.

Shavano Music Online - Building an Audio Snake

[ckvox]

Originally Posted by ritelec

did a search..........not knowing..........curious.

Shavano Music Online - Building an Audio Snake

Slightly different config, but interesting. Thanks!

[jhbrandt]

ckvox,

Rick's link is mostly correct. The part about the panel connections are highly recommended. The console end of the snake with the little ground wire to chassis connection is unnecessary if the console is designed/built properly**. - And if the console is NOT built properly, it might cause more problems than it solves. See my last sentence.

**All equipment should be built so that the internal ground reference is from the power supply/chassis common point. No continuous connection between the ground pin (1) on the unit I/O connectors to the preamps or output driver amps. All I/O pin 1 (ground) must go directly to chassis at entry/exit connector. -AT the connector.**

This is what is known as the 'Pin 1 problem'.

As a rule, we ALWAYS hook everything up; high, low, shield - on both ends of the cables. To avoid ground loops, we run all grounds for all audio circuits (together with the other wires) together including the electrical for the audio circuits. The devil is in the details, and this is not all of them.

When in doubt, follow 'standard practice'. Some practices of using ground lift adapters and clipping the shield wires to eliminate ground loops can be dangerous.

Remember, 'If it's not broken, don't fix it'.

Cheers,
John

[DrFrankencopter]

Originally Posted by jhbrandt

ckvox,

Rick's link is mostly correct. The part about the panel connections are highly recommended. The console end of the snake with the little ground wire to chassis connection is unnecessary if the console is designed/built properly**. - And if the console is NOT built properly, it might cause more problems than it solves. See my last sentence.

**All equipment should be built so that the internal ground reference is from the power supply/chassis common point. No continuous connection between the ground pin (1) on the unit I/O connectors to the preamps or output driver amps. All I/O pin 1 (ground) must go directly to chassis at entry/exit connector. -AT the connector.**

This is what is known as the 'Pin 1 problem'.

As a rule, we ALWAYS hook everything up; high, low, shield - on both ends of the cables. To avoid ground loops, we run all grounds for all audio circuits (together with the other wires) together including the electrical for the audio circuits. The devil is in the details, and this is not all of them.

When in doubt, follow 'standard practice'. Some practices of using ground lift adapters and clipping the shield wires to eliminate ground loops can be dangerous.

Remember, 'If it's not broken, don't fix it'.

Cheers,
John

John, I agree with what you've written in this post. Maintain continuity between pin 1 wherever possible.

But the original question is a little different. In Gepco multipair snakes there is a global foil shield that goes around all the individual paired wires (e.g. in an 8 pair snake it goes around all 8 individually insulated twisted shielded pairs each of which have their own accompanying drain/shied that nominally goes to pin 1 of the individual XLRs. The question was what to do with the global shield drain/drain. Presumably, all the individual drain wires are connected to their respective pin 1's as per standard practice, but there's a single extra drain wire associated with the global shield.

In my opinion this shield should be treated like a chassis, and brought to the AC ground at one point (just like a chassis would/should be).

Cheers

Kris

[jhbrandt]

John, I agree with what you've written in this post. Maintain continuity between pin 1 wherever possible.

But the original question is a little different. In Gepco multipair snakes there is a global foil shield that goes around all the individual paired wires (e.g. in an 8 pair snake it goes around all 8 individually insulated twisted shielded pairs each of which have their own accompanying drain/shied that nominally goes to pin 1 of the individual XLRs. The question was what to do with the global shield drain/drain. Presumably, all the individual drain wires are connected to their respective pin 1's as per standard practice, but there's a single extra drain wire associated with the global shield.

In my opinion this shield should be treated like a chassis, and brought to the AC ground at one point (just like a chassis would/should be).

Cheers

Kris

You are absolutely correct. **If not using a patchbay, connect the drain wire to the console chassis & do not connect the other end.**
Cheers,
John


Sent from my GT-S5830 using Gearslutz.com

[newdigitaluser]

Originally Posted by jhbrandt

ckvox,

Rick's link is mostly correct. The part about the panel connections are highly recommended. The console end of the snake with the little ground wire to chassis connection is unnecessary if the console is designed/built properly**. - And if the console is NOT built properly, it might cause more problems than it solves. See my last sentence.

**All equipment should be built so that the internal ground reference is from the power supply/chassis common point. No continuous connection between the ground pin (1) on the unit I/O connectors to the preamps or output driver amps. All I/O pin 1 (ground) must go directly to chassis at entry/exit connector. -AT the connector.**

This is what is known as the 'Pin 1 problem'.

As a rule, we ALWAYS hook everything up; high, low, shield - on both ends of the cables. To avoid ground loops, we run all grounds for all audio circuits (together with the other wires) together including the electrical for the audio circuits. The devil is in the details, and this is not all of them.

When in doubt, follow 'standard practice'. Some practices of using ground lift adapters and clipping the shield wires to eliminate ground loops can be dangerous.

Remember, 'If it's not broken, don't fix it'.

Cheers,
John

clarify this some more please

we have a drain wire for electrical safety
and we have shields to avoid RFI andor crosstalk

i thought power related only got grounded at one end

and i thought some very old audio publications had said that you only connect the shield at one end (not sure why but that is what they said -- internet whizdumb??)

[this is for bundles like snakes - single cable runs are different - the shield is connected to the connectors at both ends]

and if you had double shields connect opposite ends of them to ground and leave floating the end next to the other shields ground

do you have any authoratative sources to read more about the cabling/shielding/grounding practices ?

[ckvox]

Thanks everyone for your valuable input. Very helpful.

Have a wonderful New Year!

[ritelec]

HI.

WAS THIS

Originally Posted by DrFrankencopter

I would connect one side of that drain wire to your patchbay earth, or wherever your other chassis grounds return to. Leave the other side floating.

Cheers

Kris

KINDA THIS?

Originally Posted by jhbrandt

You are absolutely correct. **If not using a patchbay, connect the drain wire to the console chassis & do not connect the other end.**
Cheers,
John

Thanks for the post.

Rich

[TRV]

Originally Posted by jhbrandt

You are absolutely correct. **If not using a patchbay, connect the drain wire to the console chassis & do not connect the other end.**
Cheers,
John

So just to be sure that I'm understanding this appropriately, you would suggest connecting the master drain to the mixer/patchbay chassis ground but not the panel ground? The reason I'm asking is because in Rick's link above, it's showing a chassis ground connection on the panel end and an "unnecessary" one at the mixer/patchbay end.

(I apologize if this is a noobish question; I'm just starting with these things..)

[DrFrankencopter]

Originally Posted by ritelec

HI.

WAS THIS





KINDA THIS?



Thanks for the post.

Rich

Yes...

Cheers

Kris

[DrFrankencopter]

Originally Posted by TRV

So just to be sure that I'm understanding this appropriately, you would suggest connecting the master drain to the mixer/patchbay chassis ground but not the panel ground? The reason I'm asking is because in Rick's link above, it's showing a chassis ground connection on the panel end and an "unnecessary" one at the mixer/patchbay end.

(I apologize if this is a noobish question; I'm just starting with these things..)

The master shield that wraps around the snake is just a shield..it does not provide a zero volt reference for anything, only RF protection. Since it is just a shield it should only be connected on one end. Connecting it on both ends is an invitation to ground loops, and would break your star ground (if you had one to start with). Conversely, the individual shields and drain wires within the snake serve as zero volt references and should be connected at both ends (phantom power is one thing that won't work if you don't make these connections).

To me it doesn't really matter which end of the master shield you bring to ground. If you're using a patchbay, its convenient to handle all your grounds/shields there. If not, then maybe it makes sense to do it right at the console. If there is no chassis ground point available at the console, you could tie it to ground on a nearby wall outlet.

Cheers

Kris

[TRV]

Thanks, Kris. So with the shield/drain (essentially pin 1) providing my zero volt ref, I still want to connect this to the chassis ground (as in Rick's link above)?

Do the same principles apply for db25 connectors? For example, if I've got a 8 paired cable with a master drain and 2 db25 ends, is the master drain just completely open or should I still use a ground strap to take it out pre-connector?

[fitZ]

Remember, 'If it's not broken, don't fix it'.

geeeezus... Well John...what the fook am I supposed to do with the $20k worth of Snap On tools now???

[jhbrandt]

Originally Posted by TRV

Thanks, Kris. So with the shield/drain (essentially pin 1) providing my zero volt ref, I still want to connect this to the chassis ground (as in Rick's link above)?

Do the same principles apply for db25 connectors? For example, if I've got a 8 paired cable with a master drain and 2 db25 ends, is the master drain just completely open or should I still use a ground strap to take it out pre-connector?

The master shield provides that extra bit of RF protection so, yes connect it to the chassis of your console.
Simply put, you must have all RF shielding connected to the low impedance grounding node for best performance. The console chassis will be 'ground central station' if no patchbay is used. At RF frequencies many 'ground' points are high impedance. That is why these issues can get complicated quickly. Forgive my rambling ...
So, better safe than sorry. Run the overall shield to chassis at the console end.
Cheers,
John

Sent from my GT-S5830 using Gearslutz.com

[jhbrandt]

Originally Posted by fitZ

geeeezus... Well John...what the fook am I supposed to do with the $20k worth of Snap On tools now???

See if you can get your money back! Hehe! Have a happy new year Rick!! - send me an email, man.
- John

Sent from my GT-S5830 using Gearslutz.com

[TRV]

Originally Posted by jhbrandt

The master shield provides that extra bit of RF protection so, yes connect it to the chassis of your console.
Simply put, you must have all RF shielding connected to the low impedance grounding node for best performance. The console chassis will be 'ground central station' if no patchbay is used. At RF frequencies many 'ground' points are high impedance. That is why these issues can get complicated quickly. Forgive my rambling ...
So, better safe than sorry. Run the overall shield to chassis at the console end.
Cheers,
John

Thanks, John! One more question before I'm through hijacking this thread: is it necessary to tie pin 1 from one of my panel jacks to the chassis/panel ground? If so, am I correct to assume I would only tie pin 1 from ONE of the connectors? I guess the gap in my current knowledge with these grounding questions deals with the difference between master shield vs. pin 1 shield in terms of grounding to the chassis. I understand what pin 1 does for the audio ground, but I'm not sure when (and at which end) I need to tie pin 1 to chassis ground as well.

Thanks again!

[DrFrankencopter]

Originally Posted by TRV

Thanks, John! One more question before I'm through hijacking this thread: is it necessary to tie pin 1 from one of my panel jacks to the chassis/panel ground? If so, am I correct to assume I would only tie pin 1 from ONE of the connectors? I guess the gap in my current knowledge with these grounding questions deals with the difference between master shield vs. pin 1 shield in terms of grounding to the chassis. I understand what pin 1 does for the audio ground, but I'm not sure when (and at which end) I need to tie pin 1 to chassis ground as well.

Thanks again!

You should not be tying pin 1 to any chassis grounds. Pin 1's on your XLR's are your ground reference. It is up to the gear manufacturer to handle the chassis grounds properly.

The only time you need to tie a cable to chassis is in the case identified in this thread where there is a shield that goes around a whole wire bundle, as in the gepco cable shown below:



Note the silver wire at the bottom of the image. This is the drain for the shield that goes around the whole bundle. There is no Pin 1 associated with this drain wire. If your snake does not have this shield (and I suspect most of them do not), then there's no need to worry...

All the other drain wires are connected to their respective pin 1's (e.g. the silver wire in the red jacket goes to pin 1 on the XLR on one end, and it's equivalent..possibly a pin on a dSub on the other end).

Hope this helps

Kris

[TRV]

Crystal clear. Thanks, Kris!

[Devon8822]

This is still unclear for me, what do I do with the global drain wire?

[Speedskater]

There seems to be some confusion in post #23.
The XLR pin #1 is not the audio or circuit ground, it is a shield and should only be connected to the chassis.
The snake cable drain wire is a shield and should only be connected to the chassis.

While it's true that:

a] The shields are connected to the chassis.
b] The audio or circuit is most probably connected to the chassis.
c] The Safety Ground/Protective Earth (EGC/PE) is connected to the chassis.

Each of these connections is doing a separate function.

[DrFrankencopter]

Originally Posted by Speedskater

There seems to be some confusion in post #23.
The XLR pin #1 is not the audio or circuit ground, it is a shield and should only be connected to the chassis.
The snake cable drain wire is a shield and should only be connected to the chassis.

While it's true that:

a] The shields are connected to the chassis.
b] The audio or circuit is most probably connected to the chassis.
c] The Safety Ground/Protective Earth (EGC/PE) is connected to the chassis.

Each of these connections is doing a separate function.

Pin 1 is the reference for phantom power. It's more than just a shield.

Cheers

Kris

[jhbrandt]

Originally Posted by Devon8822

This is still unclear for me, what do I do with the global drain wire?

Connect only to the console chassis or Patch-bay main ground.

Cheers,
John

[Speedskater]

Originally Posted by DrFrankencopter

Pin 1 is the reference for phantom power. It's more than just a shield.
Cheers
Kris

Yes, that's very important! XLR pin 1 is the power return for phantom voltage. So a balanced mic cable must have it's shield connected at both ends.

[Speedskater]

Originally Posted by jhbrandt

Connect only to the console chassis or Patch-bay main ground.
Cheers,
John

Probably the real question is:
What if a snake cable has a breakout box at one end?

My thought would be to connect the global drain/shield to the breakout box chassis. And to connect each channel's drain/ground to it's XLR pin 1, but not to the breakout box chassis.