stjimmy76 Posted July 27, 2012 Share Posted July 27, 2012 Hi, I have an LD400pro. Amazing power/value for money 400 watts & 2x10 speakers for £240! Any way it has a "GND Lift" button, but I have no idea what it does, it's pictured in the manual but not explained. Thoughts anyone? Quote Link to comment Share on other sites More sharing options...
andydye Posted July 27, 2012 Share Posted July 27, 2012 A quick google brings up the following explanation (quoted in full below): [url="http://answers.yahoo.com/question/index?qid=20110514002533AAlhrrX"]http://answers.yahoo.com/question/index?qid=20110514002533AAlhrrX[/url] There are very limited instances where lifting that ground could potentially be dangerous, but they are few and far between. Being "Grounded" refers to providing a path into the earth - literally "the ground" - where stray electrical voltage could go if something shorted out or something else bad happened. You want that power to go to the ground through that wire... NOT through your body. If the amp is not properly "grounded" and there is a short-circuit... that voltage could wind up coming down your guitar cable into the metal parts of the bass/guitar... stirings... hands.... and down through your body into the ground through your feet. You feel that potential as a "shock" or a "tingle" when you touch something else that is sitting on the ground. Your mic stand... mic.... light poles.... other equipment.... those could all be paths to ground. Problem is your heart is between your hands and your feet... and If enough current goes through your heart - it could cause it to stop beating. That's how people die from electrical shock. But don't freak out. First - Remember that every piece of equipment sold in the USA has to be "UL - Underwriters' Labs Certified" and it has to meet all electrical codes. If that switch was going to kill you it would NOT be on the piece of gear. Canada, the UK, and most other developed nations have similar regulations. 50 years ago the grounding issue was a much bigger danger than it is today, for a bunch of reasons- today the laws and regs are much tighter and building wiring is usually much safer and better grounded. Second - there are plenty of older electrical systems in buildings where you may be playing that are not properly grounded at all... even if they have 3-prong outlets the ground wire might not be doing anything. In that case it won't matter whether you lift the ground or not - either way your amp is not grounded and there is some risk of you getting a shock. . Sometimes, your amp might have more or less "ground potential" than another amp, or the PA system, or something else on that circuit... in which case you'll hear it as "hum" "buzzing" "crackling" etc. Low-pitched 60-cycle hum is the most common annoyance. Lifting the ground on your amp MIGHT help reduce the noise. That's why the switch is there. 60-cycle hum can ruin a live show or a recording. If you do lift the ground on your amp and then hear buzzing when you touch your strings, or the buzzing stops when you touch your strings ... that's a sign of potential trouble. That means your body is in the ground loop. In that case you should probably go looking for a larger grounding problem. Again remember - that switch would not be allowed to be on the amp if it was considered dangerous, so don't be afraid to try it if it will solve a problem with a gig or recording. That said - use common sense and keep in mind that electrical current CAN kill you - if you're playing somewhere and the wires are hanging out of the wall, or if you're playing outside and it looks like rain is on the way.. those are not the times to lift the grounding from your amp. Get professional help - make the club fix their wiring instead. Quote Link to comment Share on other sites More sharing options...
stjimmy76 Posted July 27, 2012 Author Share Posted July 27, 2012 Interesting, thanks for the info, If it was labled earth lift I'd have understood. Ground must be the U.S. term for earth. Quote Link to comment Share on other sites More sharing options...
charic Posted July 27, 2012 Share Posted July 27, 2012 Not just a US term I came across it regularly during my Music Tech course Helps stop hum in that particular case btw Quote Link to comment Share on other sites More sharing options...
stingrayPete1977 Posted July 27, 2012 Share Posted July 27, 2012 Does it not only lift it from the DI socket anyway? The chassis of the amp is earthed in a fixed manner near the cable entry so Im 99.99% certain andydye's very good and informative post is mostly nonsense When everything is connected including your DI out you can create an earth loop between everything in the room I guess this creates a basic magnetic pickup? Quote Link to comment Share on other sites More sharing options...
icastle Posted July 27, 2012 Share Posted July 27, 2012 The ground lift only isolates the DI socket from the common earth. The mains earth is still present and connected to the rest of the amp. Quote Link to comment Share on other sites More sharing options...
stingrayPete1977 Posted July 27, 2012 Share Posted July 27, 2012 [quote name='icastle' timestamp='1343411533' post='1750448'] The ground lift only isolates the DI socket from the common earth. The mains earth is still present and connected to the rest of the amp. [/quote] Thats a nicer way of saying nonsense Quote Link to comment Share on other sites More sharing options...
icastle Posted July 27, 2012 Share Posted July 27, 2012 [quote name='stingrayPete1977' timestamp='1343413043' post='1750477'] Thats a nicer way of saying nonsense [/quote] Okay. How about... If you get a humming or buzzing noise when using the DI socket - press the button. Otherwise, leave it alone, it's done nothing to you... Quote Link to comment Share on other sites More sharing options...
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