Topic: Balanced Cables

[admkrk]

I need to build a couple new sets of cables and I cannot remember, or find a definitive answer on, if both sides of the ground should be tied to the shield or if one side should be lifted. If I take apart my old cables to look, I might not get them back together and I would rather not sacrifice working cables to find out. I am thinking I floated the mic end, but who knows?

[dgodwin]

When I make mic cables I connect both ends to the shield.

[jerryfreak]

in order for signal to remain balanced so that the receiving equipment can reject it, it should be wired straight through

[jerryfreak]

in order for signal to remain balanced so that the receiving equipment can reject it, it should be wired straight through. shield pin 1 on both ends

[admkrk]

Cool, Thanks!

[DSatz]

Even among engineers with decades of experience, who have actual degrees in electrical engineering, there is controversy about this question. I've listened to both sides and have respect for them both. It isn't nearly as simple or clear-cut as some answers here have implied. There is an AES standard that covers this, but plenty of smart people shrug their shoulders at it and don't follow it.

The diverse, perverse nature of interference means that you have to stay flexible, and sometimes try a succession of different methods to solve it. A methodical approach is generally a good thing--but thus far, I've never seen one that will solve all interference problems in all situations. When you have a nasty hum or cell-phone breakthrough or a heterodyne (whistle tone) in your signal line, if you can later say "I made the problem go away" then I give you full credit for success, regardless of what you believe or don't believe about anything. If OTOH you have the right theory but you can't make the problem go away ... then not so much.

--During my misspent youth, I favored connecting pin 1 to the XLR shell on both ends of the cable, and took it for granted that that was the obvious and only way to go. But at this point, I prefer to have no direct (DC) connection on either end. Capacitive coupling as provided by Neutrik "EMC"-series XLR connectors is a relatively recent approach that can help suppress radio-frequency interference--and to what's left of my mind, that's the best solution so far, though it's no panacea.

The point is somewhat moot anyway since all microphones (that I'm aware of) hard-wire pin 1 both to signal ground and to their housings--as do most preamps, mixers and recorders, though some professional models allow ground and shield to be connected or disconnected at will.

Incidentally, that's why we're all warned never to saw off the ground lug on AC power cords, or work around a three-wire AC plug with a two-prong adapter: If an (AC-powered) preamp, mixer or recorder develops a ground fault, you presumably don't want all the microphones to suddenly carry AC line voltage on their housings; one or more performers might be the lowest-impedance path to ground.

--best regards

[admkrk]

I had to laugh at the end, it reminded me of an old Emergency 51 (or whatever it was called) episode.

Anyway, one of the things that confused me was from here. It starts off saying both ends is the best way, but farther down recommends one end lifted.

[Walstib62]

A major consideration for this is how the equipment is being powered. AC line powered devices are generally more prone to introducing noise (specifically 60hz) into the signal path by means of either poor internal device grounding or leakage current of electronic components in the device. Battery powered devices are less likely to have these types of issues.
If you ground one end of a balanced cable and leave the other end ungrounded, you have just created a very good antenna for interference.