Japhet Posted May 8, 2018 Share Posted May 8, 2018 Can anyone tell me how safe it is to use the ground lift switch on my amp? If the thing has a circuit to earth I'm assuming that it's there for a reason and surely disconnecting the earth has a few inherent issues. I get a few problems in a couple of places we play where using the ground lift stops my amp from humming but I'm not too sure how advisible it is to do this. Quote Link to comment Share on other sites More sharing options...
Leonard Smalls Posted May 8, 2018 Share Posted May 8, 2018 Ground lift exists to disconnect the earths of connected equipment to prevent earth loop hum... So it doesn't actually disconnect the earth connection from the equipment, only from the return cable in an xlr in/out. 1 Quote Link to comment Share on other sites More sharing options...
Leonard Smalls Posted May 8, 2018 Share Posted May 8, 2018 If you're getting hum on an un-connected amp or combo that's another problem entirely - perhaps it's worth Portable Appliance Testing the amp to make sure there isn't an earth problem? Otherwise, a 230V isolating transformer may help... 1 Quote Link to comment Share on other sites More sharing options...
Japhet Posted May 8, 2018 Author Share Posted May 8, 2018 7 minutes ago, Leonard Smalls said: If you're getting hum on an un-connected amp or combo that's another problem entirely - perhaps it's worth Portable Appliance Testing the amp to make sure there isn't an earth problem? Otherwise, a 230V isolating transformer may help... The hum is worse if I go through my pedal board and also gets louder depending on where I stand. This only seems to happen in a couple of venues we play. The guitarist gets the same problems to a lesser extent. Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted May 8, 2018 Share Posted May 8, 2018 If the ground lift stops your equipment from humming, it's probably doing its job. All the stuff has to be earthed, but preferably only earthed once, otherwise, in some cases, tiny currents can circulate between these multiple earths, giving off hum. The ground lift will break this 'earth loop', but the equipment is still earthed, by the other part of the circuit. It's just no longer being looped. Use the ground lift, then, if it stops the hum, as you're still protected by he rest of the earth circuit. Hope this helps. 1 Quote Link to comment Share on other sites More sharing options...
Mottlefeeder Posted May 8, 2018 Share Posted May 8, 2018 Picking up on what others have said, there are two types of earth 1) A safety earth designed to blow the fuse quickly if there is a fault 2) A signal earth - often the return path of your signal circuit, or a screen to protect your signal circuit. The green/yellow wire in your mains plug is type 1, the screen in your instrument cable is type 2. The earth lift is designed to break the circuit of a type 2 earth where it might conflict with a type 1 earth, as with a DI signal between two items of mains-powered equipment. Hum can be caused by having two earth paths to a piece of equipment, ad DAD3353 mentions, but can also be caused by noisy electronics on the same circuit, or close by. The fact that the hum is location dependent, and also affects the guitarist's passive instrument, makes that the most likely culprit in my opinion. So, in those problem venues, try and identify any local lighting, gaming machines, etc, which may be plugged in to to the circuit you use, and see if the hum goes away when they are switched off. Fluorescent lighting would be an obvious candidate. David 2 Quote Link to comment Share on other sites More sharing options...
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