Connect wire shield to only one side

[ta240]

I keep seeing comments saying that when using a shielded wire, where the shield doesn't carry any of the signal, to only connect it to ground on the source side. The claim is that any noise the shield picks up will then be sent to ground instead of the next component up.
From an electrical standpoint does the noise really only go away from the next component or isn't it getting dumped onto the ground line going to still end up with it in that component?
If the noise automatically goes towards ground then it does it really matter if it is connected 3' away from the component or 3"?

 

[pma]

You must have a reference ground defined between 2 components. In case of balanced line and not used COM wire, the CMV may even destroy the input in case of source floating (class II equipment), not mentioning the possible hum. Do not do that. In case of SE link, you may use twisted pair and shield connected at source side. It will work, but HF EMI immunity will be compromised.

 

[DVDdoug]

All standard audio cables are grounded at both ends, and that's usually best.

With regular unbalanced connections (RCA, etc.) you need a common ground between the equipment. The signal needs a "reference". Voltage is meaningless without a reference... A multimeter has two connections and you read the voltage difference between two points.

If you have a ground loop (multiple ground connections) and ground loop noise, eliminating the extra ground(s) should help. Ideally, you should remove the other grounds and keep the audio ground if it can be done safely. (You shouldn't remove the power-line ground, but some people do.)

If there is no (audible) ground loop noise, keep the grounds at both ends.

With balanced connections (XLR, etc.) it doesn't matter as long as the shield is grounded somewhere so it's OK to use the standard wiring, grounded at both ends.

 

[ta240]

I should have been more clear.
Something like this in an unbalanced connection, so you have the signal and the ground inside the shield.
I often hear that you should only connect the shield to the source side to prevent any noise the shield picks up from going into the next component in your chain. But since it is connected to the ground line that is also connected to the next component does it really keep the noise away from the next component?

 

[somebodyelse]

With balanced connections (XLR, etc.) it doesn't matter as long as the shield is grounded somewhere so it's OK to use the standard wiring, grounded at both ends.

That's not entirely correct. If the shield is grounded only at the receiving end the CMRR is worsened (ref. Jensen Transformers' AN007 section 3.6) If you have to disconnect it at one end (break a ground loop) then disconnect at the receiving end.

 

[ta240]

Unbalanced connection, assume there is nearby noise being radiated into the line:

Will the noise on the device connected to the output side really be different if it is connected this way instead?

The claim that I frequently see is that with it connected the second way, any noise that is picked up by the shield is sent to the source ground and not the next (amplifier) component.

 

[somebodyelse]

See Jensen Transformers' AN007 sections 2.3 and 2.9 for some explanations. The rest of it is well worth a read as well.

 

[Speedskater]

With line level XLR balanced interconnects, the shield is sometimes only connected at the 'send' end. But that will hurt RF interference rejection, so they make a hybrid connection at the receive end using a RF capacitor.

With phantom powered microphones, the shield needs to be connected at both end.

With RCA unbalanced interconnects, using a multi-core cable and not connecting the shield will result in more Common Impedance Coupling noise.

 

[DonH56]

The only reason to disconnect the shield of a balanced cable at one end that I consider useful is to break a ground loop. Pro DI boxes (active electronic or passive transformer) often include a switch for just that reason. As others have said, it hurts HF noise rejection (how much depends upon cable construction), and makes the cable unusable for applications requiring the ground link (e.g. phantom power for microphones or other devices).

IME/IMO/etc. - Don

 

[ta240]

The only reason to disconnect the shield of a balanced cable at one end that I consider useful is to break a ground loop. ....

Not balanced, unbalanced. The two center wires are the only ones used for the signal.

With RCA unbalanced interconnects, using a multi-core cable and not connecting the shield will result in more Common Impedance Coupling noise.

The shield is connected to ground, but only on one end. I'm questioning the claims on many DIY threads that it make a difference having it only grounded on one side because the noise somehow knows to just go to the source side and then leave.

Lets back up and use a different 'cable' as an example. Some people that make their own power cables using shielded wire only connect the shield to the plug side ground wire. The theory there is the same, any noise that is picked up by the shield gets sent to the outlet ground instead of the equipment ground. But since the outlet ground and he equipment ground ends of the wire are connected doesn't the noise go everywhere?

It is the same theory with the RCA interconnects. The two center wires carry the signal and the outside shield is grounded only on the source side to keep the noise the shield picks up away from the amplifier side.

Picture it as if you took a regular RCA interconnect and added a faraday cage around the cable and just grounded the cage to the source side RCA connector. Wouldn't just as much noise from the cage make it into the amplifier with it grounded on either side of the cable or both sides?

 

[DonH56]

Not balanced, unbalanced. The two center wires are the only ones used for the signal.

I would just use a coax in that situation. Connecting the shield of a "balanced" cable at one end prevents ground currents from circulating in the "signal" ground but reduces RF rejection. Convention is to tie ground at the source. I have read arguments with pros and cons wither way, not sure it really matters. The "pro" argument is that the source is the lowest impedance so least impacted by ground (noise) currents, whereas the load is generally high impedance and potentially more sensitive to the noise, but of course the actual coupling path from shield to signal ground is important.

 

[pma]

With line level XLR balanced interconnects, the shield is sometimes only connected at the 'send' end.

This is a terrible mistake that may damage the receiver by common mode voltage!!!! Will you guys ever understand the basics? This will work only in case of two class I units when the reference common is created via PE ground wire. In case of class II units the receiver may be destroyed.

 

[DonH56]

This is a terrible mistake that may damage the receiver by common mode voltage!!!! Will you guys ever understand the basics? This will work only in case of two class I units when the reference common is created via PE ground wire. In case of class II units the receiver may be destroyed.

It depends upon the common-mode voltage and bias circuitry of the transmitter and the receiving circuitry. Professional audio components often include the provision for lifting the ground at one or both end(s), and/or are active devices with defined common-mode reference or transformer coupled with a ground reference being the transformer's center tap (at either or both ends). I cannot recall damaging a receiver in decades but have not been doing pro audio stuff for many years, and when I did blow a receiver it was due to unexpected (and undesirable) application of phantom power.

 

[Speedskater]

Not balanced, unbalanced. The two center wires are the only ones used for the signal.

That's just asking for more Common Impedance Coupling noise (power line related) noise.

See Bill Whitlock seminar page 61:

https://indianaaes.org/wp-content/uploads/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Or Blue Jeans Cable paper:

Hum Rejection in Unbalanced Audio Cables -- Blue Jeans Cable

Bah! The Subwoofer Hum Bug, and How to Stop It-- Blue Jeans Cable

 

[restorer-john]

Not balanced, unbalanced. The two center wires are the only ones used for the signal.

That cable itself is not suitable for unbalanced connections. As Don said, use coax (100% shielded single conductor).

With two core shielded (like microphone/instrument), the shield will always have the lowest resistance which is what you want, and the two internal conductors will often have significant capacitance to one another as they run parallel in most cases, not twisted. You don't want that.

 

[Blumlein 88]

That cable itself is not suitable for unbalanced connections. As Don said, use coax (100% shielded single conductor).

With two core shielded (like microphone/instrument), the shield will always have the lowest resistance which is what you want, and the two internal conductors will often have significant capacitance to one another as they run parallel in most cases, not twisted. You don't want that.

Yes +100 on this for DonH56 and restorer-john. If you have a choice, make life simple and use coax. Get something inexpensive with RG6 probably will be called digital audio or video cable. That will do fine and be well shielded.

 

[Audiofire]

RCA interconnect shield connection: to source or receiving end?

Warning: audiofool content (18+):) I guess that have been asked like thousand times but I just need to get it clear? so... We have "balanced" RCA cable structure: two isolated signal wires and separate/external foil shiled tube+drain wire touching it. Proper structure mean that shield/drain is...

www.audiosciencereview.com

 

[Cbdb2]

Unbalanced connection, assume there is nearby noise being radiated into the line:
View attachment 370656
Will the noise on the device connected to the output side really be different if it is connected this way instead?
View attachment 370664

The claim that I frequently see is that with it connected the second way, any noise that is picked up by the shield is sent to the source ground and not the next (amplifier) component.

You are correct, if the shield is only connected at one end its still connected to the ground on the other end thru the ground line. But connecting the shield at both ends (even with a cap) reduces the impedance to ground which reduces the RF interference coupled to the receiver, usually, but we are talking about RF so shield impedance, lenght?, can cause the rejection to vary with frequency, so results may vary.
And after all that, as stated several times this is the wrong cable for unbalanced connections, use coax.

 

[Audiofire]

And after all that, as stated several times this is the wrong cable for unbalanced connections, use coax.

Although RCA cables use coaxial construction (sometimes).

 

[restorer-john]

Although RCA cables use coaxial construction (sometimes).

Pretty much always did, until the audiophools got into twisted pair LAN cables, pro-mic cable and other dubious cable geometries.

The introduction of CD players resulted in high level signal exchange (2.0V), with low impedances (<1kR) and with that came the ability to basically use anything as an "interconnect"*.

Prior to CD, signals were lower (</=~150mV), of a higher source impedance, and prone to noise.

*I hate that term.