Unshielded XLR cable; question...

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WhinyLittleRunt

WhinyLittleRunt

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I'm building an XLR patch panel on the wall under my studio window that will connect to the back of my console (er, Tascam 388). I got a very nice panel off the auction site that was all Switchcraft female connectors and just needed to be cleaned up. I then bought the twist-type Switchcraft male connectors which would run from the back of the panel into the console.

As far as cable goes, I am using some cable that I salvaged from a Neotek Series 1 recording console that we got into my buddy's studio a while back. I really saw no need to buy cable when this was used for the same purpose. There were three different types of cable, some were shielded, some were not. I did a test with the un-shielded gray cable as an instrument cable (just for giggles) to see what kind of noise it would pick up. Well, it amplifies every little thing it touches or hits. Pretty much expected that. But in the application I'm going to use it for, I didn't think that would be an issue. Plus, the grey cable was more abundant so that I could keep my runs even and long enough to reach the console with room to give but not too long (prob 2 ft approx.) So I soldered one cable and tested my patch panel. My test was going direct into my Yamaha HS50 monitor. Before plugging anything in there was a constant buzz. When I connected a mic, buzz went away and all was happy.

So here's my question -
1. Is unshielded cable ok to use in this application if it isn't being moved? Will it pick up interference from the other cables?
2. Was using an active monitor to test with not really a good test? I have my Tascam packed up at the moment so that was all I had available with a balanced input and power...
3. Would shielded cable just be overall smarter to use? I really didn't want to spend any more money on this stuff since we had such an overabundance of cable left, but if worst came to worst I could probably pull out matching lengths of shielded cables.
 
So are there three conductors in the cable and no shield, or two conductors and no shield?

Regardless, I wouldn't recommend it. Its not just the issue of the shield being there to absorb unwanted RFI, its also there to tie audio grounding between devices. That's a whole 'nuther topic. It'll *work* but I know I wouldn't do it.
 
What Cory and Mike said....

About the only thing unshielded cable is good for in audio hook-ups...is when going from amps to speakers.
 
Ever use a telephone?

But if you are trying to use this for condenser mics, you need a return path for phantom current. So no good there (although your patchbay chassis could provide that). Between line-level devices, OK . . . if your cable is really twisted pair *and* your devices have good CMRR. Maybe not given your unterminated noise.
 
Jon, I believe there's more to you than meets the eye sir.
 
Pass audio for a few miles, yeah, until they get long enough to act as a transmission line at audio frequencies. Then you have to start worrying about termination.
 
Alright...

So I did a little more research on what exactly it is I'm using here. I'm not sure why I didn't do this earlier but I didn't even think the cable was labeled...

The cable in question that I thought was unshielded is actually shielded; it is Belden M 9451.



There are other cables in the pile.. unnamed and the jacket is looser...



This is what I'm aiming for (x12):




So it appears I may be using some decent cable, from what I've read. I have to think it was decent as it was being used on a Neotek broadcast console at Yale University at one point in time.

What is the lug directly in the middle of the female XLR pins? Would the shield inside tie to that? I don't like asking stupid questions but the shield is near impossible to keep intact when stripping the wire jacket as it's only foil...
 
Belden is good stuff, and that looks like shielded cable. It's perfect for permanent installations, since it has the foil shield, which is 100% coverage, but not the best choice for mic cables. For them, you want the shield to be the braided kind, as it is flexible, though a bit less than 100% coverage.

I see you got some of those new design Switchcraft XLRs....I just bought 48 male and 48 female of the same kind. I wanted the Neutriks, but these were substantially cheaper through Sweetwater ($2/XLR).
Anyway...I like them, they look like you could drive a tank over them without busting them up. :D
 
That's the chassis tab; we could have a long argument over whether to connect it, but in a proper system that has chassis ground straight through you connect pin 1 to it--using the drain wire, not the foil shield.
 
WhinyLittleRunt said:
What is the lug directly in the middle of the female XLR pins? Would the shield inside tie to that? I don't like asking stupid questions but the shield is near impossible to keep intact when stripping the wire jacket as it's only foil...
Click to expand...

You don't tie the foil to the pin...you tie the bare wire which is making contact with the foil shiled...that is your ground/shield, and that goes to PIN 1.
I would put the red wire to PIN 2 (+/Hot) and the Black wire to PIN 3 (-/Cold).

The lug is there if you should want to tie the ground/shiled also to the casing...sometimes you do, sometimes you don't.
I only add that if there is an issue or some manufacturer specifically suggests it for their gear.

Here is all the info you will need about wiring Bal/Unbal connectors:

Grounding and Shielding Audio Devices

Sound System Interconnection
 
Jon Stoppable said:
That's the chassis tab; we could have a long argument over whether to connect it, but in a proper system that has chassis ground straight through you connect pin 1 to it--using the drain wire, not the foil shield.
Click to expand...

Right...it's one of those "in a perfect world" situations, but more often than not, it becomes a "sometimes you do, and sometimes you don't" kind of answer. :D

It always depends on the two pieces of gear you are connecting and how their audio & chassis grounds were done.
 
Well I just did a different test using a dynamic mic into my Mackie VLZ3 and my patch panel and here's what I found -

There is a substantial buzz when the panel is connected just to the mic pre on the Mackie. I mean nothing plugged into it. When I plug the mic in, it pretty much goes away until you start raising the volume and you can still hear the buzz throughout. Then, I short the drain wire to the negative terminal; problem gone. Then I checked my wiring... backwards... :-/
 
I build all my own gear so grounding to chassis is always done properly. Solves all problems.
 
Jon Stoppable said:
I build all my own gear so grounding to chassis is always done properly. Solves all problems.
Click to expand...

Well don't hold out.....

Are you just a "tinkerer", doing basic stuff and/or kits....or do you get into involved builds?
What kidnd of gear do you build...anything for others, or just for your personal use?
 
I don't do kits; how would I know if they were properly designed? In time it took me to analyze them I could simply build my own design.

Proper chassis grounding is the simplest thing in the world. It's right in that Rane note you linked. Obey it and you can ignore all of the rest of that note.

Good ground plane design is slightly trickier, but nothing too hard until you get into mixed-signal and controlled impedance circuits, etc.
 
It's nice having audio gear builders here on the fourms.

Why...we just had one around here until yesterday, when he got upset over nothing all that serious. I mean there was no real bad intent, he just took it that way. *shrug*

But as soon as he decided to step off the forums...here we get a new audio gear builder in his place!
Is that cool or what? :cool:

Kinda like that Seinfeld episode where Jerry always has everything balance out for him.
He looses $20...then he finds another $20...etc...etc. ;)
 
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