Disconnecting pin #1 on XLR.

[Telecruiser]

I have been told that when patching between rack effects with balanced I/O's that I should disconnect pin #1 (ground) on one end of the cord to prevent additional noise and hum. They didn't say anything about mic cables.

 

Anything to this?

[soul-x]

I definitely wouldn't say "should."

 

But lifting the signal ground is one potential workaround when there is grounding related noise problem. Lots of devices are already configured to do it with a switch or something on them.

[agedhorse]

On;y sometimes. Doing so without understanding when, where, and why can lead to RF problems however. There are multiple ways to do this.

[Dogoth]

It depends.

 

Sometimes a ground lift aleviates a ground loop. As long as the shield is still "grounded" at one end or the other, you're covered (small pun there). The trick is knowing which end is best. Often it's hard to tell.

[W. M. Hellinger]

 

It depends. Sometimes a ground lift aleviates a ground loop. As long as the shield is still "grounded" at one end or the other, you're covered (small pun there). The trick is knowing which end is best. Often it's hard to tell.

 

 

I would think the shortest and/or least encumbered and/or most reliable path to ground would be best.

[agedhorse]

The problem with just ground lifting is that there are 2 different grounds (ground paths) carried through all these ground connections. There are low frequency grounds which are audio and below, and there are RF grounds which are typically 500kHz and above, these RF issues can be oscillation related events or intrusion and detection of RF radiated into the area. Often, especially in high RF environments, the RF ground MUST remain intact, commonly through a very small, high frequency decoupling network like a parallel RC with a -3dB point of say 250kHz or higher between pin 1 and the system ground.

 

Anybody who has designed products with digital, switchmode or class D technology should be familiar with this specific topic. When is a ground not a ground? When the frequency changes. Even 20kHz audio can create an issue if layout is poor.