By default, audio cables have their ground pin connected to the cable shield at both ends. I have seen recommendations to connect the cable shield at one end only, to avoid ground loops.

What's the best way to handle this in practice? There's lots of equipment without 'ground lift' switches, so it could be convenient to have the cable shield connected at one end, but the linked article mentions there are some potential problems with that.


Universal Balanced Audio cables need two signal lines and one ground line fully connected at both ends. Generally the wiring is:

Signal + > Pin 2
Signal - > Pin 3
Ground   > Pin 1

Disconnecting pin 1 at both or one end, will have the effect of removing the ground connection between the two ends. This can be useful in avoiding audio ground-loops in certain situations, however it will completely prevent the use of this cable as a microphone cable for condenser mics, as it does not allow Phantom power to be passed.

A cable such as this can be used for the transmission of line-level signals as only pins 2,3 are required.


Because I live in the UK, where earth pins are compulsory & all building wiring is earthed, I've always gone for comprehensive grounding/earthing of all components & all signal paths.
I terminate any structure at a single socket or single phase node of a common ring, if at all possible.

If I am ever faced with potential ground loops because, for instance, another part of the installation may be remote from me - a PA handled by a separate company, wired off potentially another phase or ring, then I have my "secret weapon", which I acquired from the BBC over 3 decades ago when I worked there.

It goes by the unsalubrious moniker of a "buggery box". No doubt it did at one time have an official name, but that is apparently lost to the mists of time & they've been called that since BBC engineers wore brown lab coats.

Essentially, it is a 1:1 isolating transformer[1] inside a steel case you couldn't damage with a sledgehammer. I'm not sure what else is in there other than about 10 kg of very heavy copper winding.
Plug your own stage rig into that - no ground loops, no chance of getting electrocuted.

Back in the old clockwork analog days, the BBC used to put one of these on every single piece of equipment on an outside broadcast & also had similar devices for any sonic connections too, 1:1 XLR & bantam jacks in effect, so that no piece of their equipment was ever connected directly to anyone else's.
I always reckoned if it was good enough for Auntie Beeb, it was good enough for me.


Isolation transformers block transmission of the DC component in signals from one circuit to the other, but allow AC components in signals to pass. Transformers that have a ratio of 1 to 1 between the primary and secondary windings are often used to protect secondary circuits and individuals from electrical shocks between energized conductors and earth ground. Suitably designed isolation transformers block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers, medical devices, or laboratory instruments.

  • You say "no chance of getting electrocuted". Am I right in thinking that this implies that the output has no real neutral side. I.e. neutral is not connected to ground at the transformer. This is how cruise ships are wired, and why power bars with surge-protectors or one-sided on/off switches are not allowed. Anyone using this setup needs to be aware of the fire danger from devices that assume that neutral isn't isolated. – Ray Butterworth Oct 26 '19 at 13:35
  • @RayButterworth - I honestly don't know enough about it to be able to answer, as I'm not any kind of electrical engineer. I used to use these "as instructed" & was given one personally by BBC lab techs at the time, with the general info I've given above. idk if this might help - powerinspired.com/isolation-transformer-need-know – Tetsujin Oct 26 '19 at 13:49
  • @Tetsujin I think the OP is referring to audio/XLR cables, not mains cables. – Mark Oct 26 '19 at 22:36

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