[Escott1377]

I am buying some wire to try and make a pair RCA interconnects.  The wire will come shielded.

Is it best to ground 1 end with the shield, ground them both, or no ground at all?

Little bit of confusing info out there about best practices.  I have always heard to ground 1 end only.

Thanks for your help on this very elementary equation.

[G Georgopoulos]

Ground/connect both ends of the shield,otherwise there is no signal tranfer of one equipment to another

cheers mate,greetings from down under...

[Davey]

Yes, there IS confusing info out there regarding best practices. 

Some RCA cables are indeed wired without a shield connection on one end.  Even some using standard (two-conductor) coax are wired this way.  Contrary to what GG says, you will most likely still get signal transfer since there will be an alternate ground path elsewhere in your system.  RCA interconnects are sometimes wired this way to prevent ground loops.  However, IMHO, you should connect the shield on both ends.

If you're using twisted-pair (three-conductor) shielded cable then you'd want to use the internal two conductors to make the RCA pin/outer connections on both ends, but connect the shield on only one end.  That end should probably be attached to the source component.

Dave.

[G Georgopoulos]

Yes, there IS confusing info out there regarding best practices. 

  However, IMHO, you should connect the shield on both ends.



Dave.

Good Boy...

[Escott1377]

Thanks guys!

[Wayner]

Coax cable actually has 3 conductors. The center conductor (1), a foil (aluminum) wrap around the center conductor's insulator (2) and a braided shield (3).

Wayner

[Davey]

  Good gosh.

Only some coaxial cable has three conductors.  However, it's correctly called "triaxial" and not "coaxial" cable.
There are three-conductor BNC connectors that are commonly used with triaxial cable.

There are certainly versions of coaxial cable where the outer conductor is formed with different layers......maybe a braided sheath over a foil as you mentioned....but that doesn't yield a third 'electrical' conductor since they are in electrical contact with each other.

Dave.

[Davey]

Good Boy...

Insults are not necessary.

Dave.

[Speedskater]

If the foil and the braid are insulated from each other then it's a triaxial cable.
If the foil and the braid are connected to each other then it's a coaxial cable.
Either when use with RCA connectors functions as a coax.

The best RCA analog interconnect cables are made with a coax that has a heavy braided shield. With the foil being optional.

[andyr]

The best RCA analog interconnect cables are made with a coax that has a heavy braided shield. With the foil being optional.

Not in my universe!

AFAIAC, the best-sounding RCA analogue interconnects are made with solid-core 'twin-ax' ... which is:
* 2x solid-core conductors (which carry the signal and signal ground), with
* a braided shield (which, if grounded) shields the signal wires inside.

I use Belden Profibus - I think its code is 3789A.

The optimum way to ground the shield is to have a 'pigtail' of shield wire (individual strands picked apart from the braid and then twisted into one wire) which connects to the earth terminal on either the source component case or the destination case.  This way, RFI picked up by the shield has no connection to signal ground.


Regards,

Andy

[DaveC113]

Not in my universe!

AFAIAC, the best-sounding RCA analogue interconnects are made with solid-core 'twin-ax' ... which is:
* 2x solid-core conductors (which carry the signal and signal ground), with
* a braided shield (which, if grounded) shields the signal wires inside.

I use Belden Profibus - I think its code is 3789A.

The optimum way to ground the shield is to have a 'pigtail' of shield wire (individual strands picked apart from the braid and then twisted into one wire) which connects to the earth terminal on either the source component case or the destination case.  This way, RFI picked up by the shield has no connection to signal ground.


Regards,

Andy

I agree for the most part, but the signal and chassis grounds are directly connected in most components. Even better would be to ground the cables' shields to the same point the components are plugged into as many components do have some isolation between safety ground and chassis/signal grounds. This could provide a very low impedance path for noise and not interfere with the signal/chassis ground. A few cable companies are currently doing this, but of course now you need ground cables for your signal cables, etc...

[andyr]

I agree for the most part, but the signal and chassis grounds are directly connected in most components. Even better would be to ground the cables' shields to the same point the components are plugged into as many components do have some isolation between safety ground and chassis/signal grounds. This could provide a very low impedance path for noise and not interfere with the signal/chassis ground. A few cable companies are currently doing this, but of course now you need ground cables for your signal cables, etc...

Signal ground does not touch mains/chassis ground anywhere in my system, anyway.

Andy

[DaveC113]

Signal ground does not touch mains/chassis ground anywhere in my system, anyway.

Andy

Ok, but these days most of the time signal and chassis are directly connected and the whole thing floats together. Shields are connected to the chassis close to the chassis jack. Sometimes, chassis/signal is isolated from safety ground by one of several methods. In this case, the shield is basically part of the chassis and in balanced equipment should be connected at both ends. For single ended only one end.

[G Georgopoulos]

Ok, but these days most of the time signal and chassis are directly connected and the whole thing floats together. Shields are connected to the chassis close to the chassis jack. Sometimes, chassis/signal is isolated from safety ground by one of several methods. In this case, the shield is basically part of the chassis and in balanced equipment should be connected at both ends. For single ended only one end.

safety ground,man oh man,what about double-insulated/battery equipment,your cables wont work...

[evsentry3]

The optimum way to ground the shield is to have a 'pigtail' of shield wire (individual strands picked apart from the braid and then twisted into one wire) which connects to the earth terminal on either the source component case or the destination case.  This way, RFI picked up by the shield has no connection to signal ground.

I like to refer to this as a "drain" rather than mix it into the description of a "ground".

And the idea is to drain to the low impedance end since that's the less likely end to have the drained signal impressed onto the desired audio.

EV3

[andyr]

safety ground,man oh man,what about double-insulated/battery equipment,your cables wont work...

If you mean components that have a battery PS, GG, the twinax interconnect will certainly do its job ... but the shield part may not work at its best:

* If the twinax IC is connecting a battery-powered device to a mains-powered, chassis-earthed device ... then the shield should be earthed to this chassis.  However, the chassis of the battery-powered device will not be earthed - so may not do a 100% good job of shielding the circuits inside.  I always earth the (metal) case of a battery-powered component either back to the earth on a wall socket or to a mains-powered component whose case is (safety) earthed.

* If the twinax IC is connecting a mains-powered, chassis-earthed device to a mains-powered, chassis-earthed device ... then the shield should be earthed to one of the chassis.

* If the twinax IC is connecting 2 battery-powered devices then, as I said, the chassis of one or other - or both - should be earthed, somehow ... for maximum noise suppression.


Regards,

Andy

[andyr]

I like to refer to this as a "drain" rather than mix it into the description of a "ground".
EV3

Yes, good terminology, EV3 - particularly as the shield is 'draining' any collected RFI to earth. 

And the idea is to drain to the low impedance end since that's the less likely end to have the drained signal impressed onto the desired audio.

Sure but in the case of twinax - where the shield is not part of the audio signal chain - the shield is not going to 'impress' anything onto the audio signal.


Andy

[Speedskater]

Signal ground does not touch mains/chassis ground anywhere in my system, anyway.
Andy

You must have very unusual equipment.
Good engineering practice, dictates that audio circuit common (and power supply common) be referenced to the chassis.

[Speedskater]

I like to refer to this as a "drain" rather than mix it into the description of a "ground".
And the idea is to drain to the low impedance end since that's the less likely end to have the drained signal impressed onto the desired audio.
EV3

Yes the word "ground" is so often mis-used, it's lost any real meaning.
While the "drain" connected to the chassis, becomes part of the shield.

[Speedskater]

Yes, good terminology, EV3 - particularly as the shield is 'draining' any collected RFI to earth. 
Andy

Well no, the RFI has no interest in the Earth. The shield is just part of the shield system.