Connect wire shield to only one side

[pma]

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.

However, I am afraid that many here still do not understand why the balanced line MUST have the shield connected at both sides. I am not talking about improper implementations that need a ground lift switch. Explained in the images below.

Floating voltage has 50Hz frequency, signal voltage has 1kHz frequency. See the saturation. This is a better case, damage may occur as well.

 

[LeadEars]

I was looking up some info on my conrad-johnson preamplifier and found the following quote in the user manual (and which reminded me of this discussion):

"Interconnect cables should be kept as short as possible (3 meters or less), and shielded cable should be used (cable which has two center conductors, and a separate external shield connected at only one end)."

I've used a lot of different unbalanced interconnects with that preamp over the last 30 years, none of them matching that description, to my knowledge. I guess it's about time I tried following the directions and see if I notice any difference. I do have a wall wart that introduces hum into the system if it's physically too close to the preamp, so maybe that could be a place to start.

 

[DonH56]

I was looking up some info on my conrad-johnson preamplifier and found the following quote in the user manual (and which reminded me of this discussion):

"Interconnect cables should be kept as short as possible (3 meters or less), and shielded cable should be used (cable which has two center conductors, and a separate external shield connected at only one end)."

I've used a lot of different unbalanced interconnects with that preamp over the last 30 years, none of them matching that description, to my knowledge. I guess it's about time I tried following the directions and see if I notice any difference. I do have a wall wart that introduces hum into the system if it's physically too close to the preamp, so maybe that could be a place to start.

Unless you have RFI issues I would not bother. Coax already does a good job of rejecting noise, and lifting the shield at one end as they describe can help reduce a the chance of a ground loop but is actually worse for noise ingress than if both ends are properly grounded.

The wall wart is likely a different problem and the simplest solution is to keep it away from the preamp.

 

[Bruce Morgen]

"Interconnect cables should be kept as short as possible (3 meters or less), and shielded cable should be used (cable which has two center conductors, and a separate external shield connected at only one end)."

That is the configuration of the original Monster RCA cables from back in the previous century -- it was apparently the basis for their arrow stickers. I nabbed a pair of those from the local charity thrift store (for $3 IIRC) and have used them to connect my processor stack to my active monitors ever since I ran into some (fortunately temporary) local EMI, which they were somewhat more effective at suppressing than the conventional cables they replaced -- whether that was due to their odd shield connection or perhaps just better shielding I don't know.

 

[raindance]

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


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?

This is a fiction that was created by Monster cable where they somehow managed to "train" their electrons which conductor to flow in . Unbalanced needs to use coax cable, a single conductor encased inside a shield for best noise rejection.

 

[DonH56]

That is the configuration of the original Monster RCA cables from back in the previous century -- it was apparently the basis for their arrow stickers. I nabbed a pair of those from the local charity thrift store (for $3 IIRC) and have used them to connect my processor stack to my active monitors ever since I ran into some (fortunately temporary) local EMI, which they were somewhat more effective at suppressing than the conventional cables they replaced -- whether that was due to their odd shield connection or perhaps just better shielding I don't know.

It's not all that odd, not uncommon to do that to break a ground loop, but only works for that if the shield and inner "ground" wires are not connected to the same chassis. That is typically only the case for balanced interconnects, so in that sense it is odd. The shield plus inner twin-lead does provide some additional noise (RFI) immunity as you saw; it is more effective if both ends of the shield are grounded.

This is a fiction that was created by Monster cable where they somehow managed to "train" their electrons which conductor to flow in . Unbalanced needs to use coax cable, a single conductor encased inside a shield for best noise rejection.

Arrows or other markings are used on some balanced (XLR/TRS) cables to indicate the end that has the shield lifted. Arrows are used on some cables to indicate which end has a passive network. And some are just for show (plenty of those, natch).

Unbalanced cables using tri-ax (inner conductor plus two shields) or inner twisted pair plus outer shield configurations are a way to increase noise rejection for unbalanced (single-ended) connections, but work best if properly implemented, with the shield and signal returns separate. Most audio cables that I have seen simply short the shield to the signal return/ground at one end, which helps "some", but in some cases can make things worse (e.g. if the length happens to match the fractional wavelength of the noise source, the unterminated shield can act as an antenna for greater noise pickup).