Ground: Loops and Lifts

[jeff]

 This is another one of those questions to try to understand how/why things work.

 I was looking at a FX unit and one one thing that struck me kinda funny was that it included a 3 to 2 prong adaptor that was to be used if needed to eliminate a ground loop.

 If the loop is caused because the 3rd prong and the output (guitar)cable are both grounded, and disconecting the green ground wire eliminates the loop, wouldn't disconnecting the output cable's ground instead also eliminate the loop?

 Wouldn't it be better to use an inslulated output jack and have a ground lift switch that disconnects the jack to ground connection?

[terminalgs]

3 to 2 prong adapter disconnects the ground loop, but, of course, it isn't safe.   The device's path to mains earth depends on the shield of a removable patch cable.  your idea to disconnect the shielding is a safer one, but you can make an FX unit completely free of ground loop noise, with a proper ground lift.  Its cheap, easy, and safe.  Valve Wizard's free grounding chapter covers it well. 


The FX Unit engineer didn't know how to make a proper ground lift circuit.  Or he thought disconnecting main's earth to chassis was acceptable.