[gordolindsay]

Why do people solder the shield in cables such as Canare Starquad or Mogami 2534 to the ground? Why not just use the wires in the cable to solder to ground?

Silly question probably but hey, it doesn't hurt to ask.

 

[bg4533]

Starquad cables are made a few different ways. There are 4 conductors and a shield. Some people use 2 conductors for L, 2 for right and shield for ground. Some use 1 conductor for L, 1 for R, 2 for ground and then connect the shield to ground on 1 side (most often the source side).

There is a lot of debate over shielding. A lot of people think connecting a shield on only 1 side is most effective.

 

[drewd]

The idea behind connecting the shield to ground on one end is an effort to use the shield for its intended purpose: to conduct EMI to ground without having that interference couple onto the signal wires.

The ground wire, even though it is supposed to be at a fixed voltage, can vary if some sort of EMI event is coupled onto it. It won't vary for long, but it will vary because there is never an instantaneous reaction to anything in an electrical circuit. And since ground is a reference, that means that that the signal wire's voltage will, for at least a moment, be altered. (Apologies if I'm preaching to the choir).

So, soldering the shield to one end of the cable shunts that signal to ground without giving it an opportunity to alter the voltage on the ground wire. The energy is absorbed by the capacitance of the source (or amplifier, depending upon which direction the cable is aimed) and noise is minimized.

Of course, one could also minimize sources of EMI and not have to worry about that sort of thing

(Easy for me to say!)

Personally, the only EMI problem that I have is with my cell phone and the noise is not coupled onto the cable anyway, so I've just learned to keep my phone away from my audio system (and my computer monitor!)

-Drew

 

[rickcr42]

The shield is only that if attached at some point to a ground and when it comes to microphone cables (or other high gain use) essential.
But for headphones it will only be terminated at a single end anyway becausue the cans are not a circuit and do not have a ground and maybe should not be used at all if you consider how a walkman radio gets the RF signal-the headphone cord performs dual duty as an antenna/headphone cable with the ground section being the antenna lead

 

[gordolindsay]

Alright, so if you want to connect the shield to ground, you want it to be at the source end huh? Which end is the source end? I'm guessing in interconnects it would be the end coming from the cd player? What about if I recabled my headphones? would it be connected at the headphone end or the 1/4" plug end? How 'bout an extension cable?

Thanks for all the information already, it helps being in the know

 

[Garbz]

The source is where the signal comes from i.e. the cdplayer. Personally I starground my shields to the best grounded equipment, in this case my amp. That said there was no real difference.

What I found though and since I live in a low-EMI area cables like Tranparent MusicLink cables float their shield and don't connect it to either side. This is worth considering if EMI isn't a problem since I believe there's a type of distortion involved with running a round shield around a signal cable.

 

[Emon]

It doesn't matter which side you connect the shield to. Headphones, amp, both, doesn't matter. It all leads to ground. I'd just solder to both sides for strength and consistency.

 

[rickcr42]

Quote:

It doesn't matter which side you connect the shield to. Headphones, amp, both, doesn't matter. It all leads to ground. I'd just solder to both sides for strength and consistency.

Actually it does matter.headphones do not have an actual "ground" being an electro-acoustical device (not electronic) better modeled as a restance/inductance like a loudspeaker so IF the ground were to be only connected at one end you want it where the grouns potential has the least resistance,right at the chassis.
To send it down a small wire,attach the shield at the headphone end and then send the shield back down "gounded" to the chassis but not attached to the chasis would cause a higher impedance ground and THAT would be a nice little RF antenna.

Thin grounded wire to heavy grounded shield going in the opposite direction

Terminal end or both ends but not headphone end only

 

[Emon]

Okay, so I suppose sending it back along the ground wire is a bad idea, although for most applications it probably isn't a large enough distance to matter. When I wrote that I was mostly thinking grounded at the jack vs grounded at the headphones and the jack.

 

[rickcr42]

Quote:

Okay, so I suppose sending it back along the ground wire is a bad idea, although for most applications it probably isn't a large enough distance to matter.

again a misconception man.

Look at how small a set top antenna is for a TV !

Now think of the length of travel of the cord from amp to headphones and back to the amp again if connected wrong !

nice little loop antenna you got there dude !

when thinking audio you still need to consider RF and what it is

 

[Voodoochile]

You definitely want to connect to ground at the source end, if you plan to connect. In many cases, the shield would not even be truly connected to ground (if terminated on the other end) otherwise, or if so, is apt to cause ground loop issues.

What is a shield if it is not grounded?

Also, Garbz referred to no shield at all if your environment is quiet enough. Making a braided Kimber-esque cable is fairly easy to experiment with. Many times it is fine as-is. It seems that typically when someone is asking about shielding or grounding, they have some noise issues.

 

[rickcr42]

Quote:

What is a shield if it is not grounded?

just a hunk of metal floating around in space

My only concern was with the statement that it did not matter which end the ground was connected.Because the impedances are low this is not a huge problem but my attitude is why look for trouble ?

Scratch that...I always look for trouble and mostly find it

but just not in my audio stuff

 

[Voodoochile]

Quote:

Originally Posted by rickcr42 just a hunk of metal floating around in space

Exactly. It stops being a shield.
I think it is too often assumed that the metal itself is a shield, but rather it is the properties of it's connection that would make it a shield.

As I understand, anyway. It has been my experience that it works pretty well, but then again I have not had a lot of trouble with noise.

 

[rickcr42]

as an add :

I would say 95% of my interconnects are non shielded and RFI has nver been a problem.Where I have always had trouble system interconnection related was always with the SATV/CATVground loops and adding in my computer as a source which brings its own set of problems fixes.These areas have all been adressed by adding inline transformer isolation.

What is even more of a b*tch is the non standard AC cord mounting.
Put audio componants in a verticle rack or even a horizontal cabinet and you have to connect everything some way or they are individual parts having no function but being AL AC powered means there is a power cord coming out the back.
My "peave" is there is no frikkin standard ! some exit the chassis on the left,some on the right,some dead nuts center.How the hell am i supposed to keep this both neat and avoid crossing AC with signal connections if there is no freakin' ORDER !
what is so damn hard with a standard that says :

"all AC shall exit the chassis on the right rear side and all power switches will be on the right front area"

Too damn simplistic ? Not screwey enough ? Not something they can charge extra for ?

"we have a solution but it's not gonna be cheap !"

Being that my connections are mostly non shielded this is an actual problem,not to mention sloppy.I like tidy and having all the Ac to one side with a single AC filter/distribution strip is tidy.Coming from all directions is not.

I mostly tackle this with shielded Beldon AC cords (the ground attached only at the terminal end) but I am at this point making the move towards "true" balanced lines for much (all ?) of my system audio connections,most definately any thing that leads to a gain stage which will only magnify problems by a factor of the gain.
This combination will/should eliminate the possibility of AC being injected into the system but still does crap for neatness.

these guys need to get on the same page here and get with a standard so I can sleep at night.

 

[gordolindsay]

Quote:

Originally Posted by rickcr42 as an add : I would say 95% of my interconnects are non shielded and RFI has nver been a problem.

Ha, I have 0% shielded interconnects (only 1 set) and have problems with RFI and EMI. But I think it's my headphone cable thats screwing me up cause when I move that it changes the noise coming through. A real pain in the you know what