ground loop toolkit

[Brian Reynolds]

Analogue audio signals are infact a varying ac voltage from just under 1 volt (line level) to almost nothing at (microphone level).
If when 2 or more pieces of equipment are connected together and running on 110-240v they will have an earth connection which is there for safety reasons and must not be removed this may not be connected to the same point in the main switch board, but this is fine for safety.
When the audio cables are connected to the equipment another earthing connection is created directly between the units and will often be a shorter distance than the “electricial earth connection” this gives a very slight volt difference between the gear and often shows up as hum.
If that earth loop is broken by removing the connection on pin 1 the hum then stops.
If an isolation transformer is used it is infact breaking the physical connection of pins 2&3, from the input of the transformer to the output, and if then you disconect pin 1 the units will be TOTALLY audio isolated from each other.
This often refered to as a “Floating” signal (NAGRA audio gear often use this)

I hope this explains a tricky subject to get your head around…

The difference between Knowledge and Wisdom is… Knowledge is the knowing of facts…. Wisdom is the sensible application of good quality knowledge…

[John Livings]

Hi All,

I found this a while back;

https://www.blueguitar.org/new/articles/other/ground_loop.pdf

I have heard of cutting the wire connection from the #1 pin and the “shell” leaving the shielding connected to the #1 pin ? ( If you look closely at your XLR connection, You will see that the #1 pin is soldered to both the cable shielding and a small wire that connects to the connector shell).

If you remove the #1 pin which is connected to both the shielding and the shell, And you were using a Condenser Mic (Phantom Power) Are you not removing the Ground to that Mic?

John

[Brian Reynolds]

Hi John, ground loops happen between pieces of gear and never between the mic and mixer, so the signals you are dealing with most times are at line level.
If you remove the connection to pin 1 in the connector the chances that some day you will need that cable for a phantom powered mic and the cable wont work.
Thats why i like a very short (100mm) XLR-XLR pin 1 lift cable in my kit… easy to insert in a line and easy to remove… problem solved

The difference between Knowledge and Wisdom is… Knowledge is the knowing of facts…. Wisdom is the sensible application of good quality knowledge…

[Ty Ford]

Good work everyone.

Thanks for helping Bob with this. He’s a good friend of mine and I’d hate to have to prematurely attend the viewing after his electrocution.

Regards,

Ty Ford

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