Quick multicore wiring question

GTE

Hello,

I have two rooms which I want to connect for audio.
I want a balanced stereo connection each way.

I was looking around at a couple of multicore by meter cables on Thomann and I am just looking for a confirmation on the wiring of the ground connection as I have never done this before.

Now, I am most likely using the term "ground" incorrectly here.

For a balanced stereo connection going 1 way can the L and R share the ground?

For a balanced stereo connection each way can the two L and two R all share the same ground or would there have to be two grounds, one for each direction?

Do the grounds have to be on the shield? Does the shield not shield if it is not connected to a ground?

Someone mentioned using a Cat5 cable for unbalanced connection and use the extra wires as the shield and I was unsure would those wires have to be connected to something to make the shield work.

I think I shall have a looks see about buying an audio wiring book, I can imagine it being very useful =D Any ones you guys use?

Thanks!
bbk

exaisle

bbk wrote: »

Hello,


For a balanced stereo connection going 1 way can the L and R share the ground? YES

For a balanced stereo connection each way can the two L and two R all share the same ground or would there have to be two grounds, one for each direction? YES and NO in that order

Do the grounds have to be on the shield? Does the shield not shield if it is not connected to a ground? it's preferable if the shield is grounded so taht any signal picked up by the shield runs to ground

Someone mentioned using a Cat5 cable for unbalanced connection and use the extra wires as the shield and I was unsure would those wires have to be connected to something to make the shield work. The idea of having a shield is to surround the wire on which the signal is carried so that any stray signal can be run to ground and nullified. Generally one would use a coaxial cable of some sort, eg instrument lead, for an unbalanced connection. Using a CAT5 cable would get you by but you'd be looking at a very inefficient shield because the wire carrying the signal is not surrounded by anything...

E

exaisle

Can you be a bit more specific about what kind of signal you intend running on these cables?

GTE

exaisle wrote: »

Can you be a bit more specific about what kind of signal you intend running on these cables?

Hello,

Many thanks for the reply.

One way will be a stereo audio signal coming from a secondary studio running to an on air mixer in a radio studio. This allows talkback to the studio and broadcasting from this secondary room.

The return would allow studio to secondary room talkback. This could be mono in real terms.

exaisle

Ah, ok. I can see why you're being picky about shields and ground now.

TroutMask

For wiring info the Rane website is hard to beat.

OK - for your purposes I would run all sends & returns fully balanced in both directions. That way, if you get ground loops, you can eliminate them by lifting the drain wire (screen) at the input of the destination device.

When referring to balanced audio, use the terms: Signal Hot, Signal Cold, and Screen. This separates out the functions of the wires between signal carrying and EMI suppression/shielding. Remember the screen only has to be connected at one end - this is how we get rid of ground loops.

I would not attempt to 'share' screen between L-R pairs: any savings in cable costs will be offset by the cost of time spent debugging and eliminating hums. Besides, some balanced outputs dislike having their signal carrying legs strapped to ground (which is what unbalancing does). Be prepared to balance unbalanced units. I would use two runs of cable/ multicore: one for the stereo program, and one for the talkback/coms. This will eliminate any possibility of crosstalk occurring between adjacent pairs.

GTE

TroutMask wrote: »

For wiring info the Rane website is hard to beat.

OK - for your purposes I would run all sends & returns fully balanced in both directions. That way, if you get ground loops, you can eliminate them by lifting the drain wire (screen) at the input of the destination device.

When referring to balanced audio, use the terms: Signal Hot, Signal Cold, and Screen. This separates out the functions of the wires between signal carrying and EMI suppression/shielding. Remember the screen only has to be connected at one end - this is how we get rid of ground loops.

I would not attempt to 'share' screen between L-R pairs: any savings in cable costs will be offset by the cost of time spent debugging and eliminating hums. Besides, some balanced outputs dislike having their signal carrying legs strapped to ground (which is what unbalancing does). Be prepared to balance unbalanced units. I would use two runs of cable/ multicore: one for the stereo program, and one for the talkback/coms. This will eliminate any possibility of crosstalk occurring between adjacent pairs.

Many thanks for that post. What was in bold is mighty interesting!
I will check out that website. =D

studiorat

bbk wrote: »

Many thanks for that post. What was in bold is mighty interesting!
I will check out that website. =D

Thing is, this kind of grounding has poor immunity to RF, since the shields act as aerials. Which could be an issue in your case.

GTE

OK, in fear of missing the point completely:

My option for higher cable costs but less hum problems in the future:
2x the following link for the stereo link from second room to on-air studio?
http://www.thomann.de/gb/cordial_cpk_220_sw.htm

Repeat for the way back if I decide on that being stereo. Even two monos. 1 monitoring desk output and 1 or the presenter mic.

TroutMask

Hi again,
you could probably get away with running the sends and returns on one length of 4-channel multicore. It would be neater. I got a length of 4 way multicore from thomann before, very useful. I always factor a few redundant channels in - saves a lot of time down the line if you need extra channels.

On the grounding issue (if it occurs, that is): lifting the screen one one end is perfectly acceptable, if RFI occurs then simply add a 200 (ish) picofarad capacitor between the screen and the system ground - this will shunt RF signals to earth.
Don't start lifting screens unless you have a ground loop problem. The other way around is to use isolation transformers, though good iso-traffos are expensive.

CAT 5 is no good for this kind of work - don't even go there.

GTE

TroutMask wrote: »

Hi again,
you could probably get away with running the sends and returns on one length of 4-channel multicore. It would be neater. I got a length of 4 way multicore from thomann before, very useful. I always factor a few redundant channels in - saves a lot of time down the line if you need extra channels.

On the grounding issue (if it occurs, that is): lifting the screen one one end is perfectly acceptable, if RFI occurs then simply add a 200 (ish) picofarad capacitor between the screen and the system ground - this will shunt RF signals to earth.
Don't start lifting screens unless you have a ground loop problem. The other way around is to use isolation transformers, though good iso-traffos are expensive.

CAT 5 is no good for this kind of work - don't even go there.

Well, this seems to be 8 way with a screen/shield. Pic is horrible.
http://www.thomann.de/gb/cordial_ccma_16.htm

That works out as just a bit cheaper per meter then 4 of the other cables per meter.

I am looking at 130 pounds to get this done at the moment. It gives some expandability, seems to keep the shields separate too.

TroutMask

there'll be a screen on each pair

TroutMask

BTW, how long of a run do you need and are you near Dublin? I might have what you need.

GTE

TroutMask wrote: »

BTW, how long of a run do you need and are you near Dublin? I might have what you need.

Based near Belfast. Funding is coming from a university committee so the stuff has to come from a company if you get me.

TroutMask

gotcha - can't cut an invoice, I'm afraid

GTE

TroutMask wrote: »

gotcha - can't cut an invoice, I'm afraid

Nay bother but thanks for the help.

So that multicore is the way to go? I think so.

TroutMask

I'd get a multi or a loom with the connectors on already - save yourself the soldering