Members pipedwho Posted December 28, 2006 Members Share Posted December 28, 2006 Originally posted by where02190 The likelyhood of an AC ground becoming disconnected in any professional system is about as likely as getting hit by lightning. In fact, your chances of getting hit by lightning are I'd bet more likely. Furthermore, should that happen, whether one or both amps are grounded makes no difference, since they would in all likelyhood be plugged into the same source, they would both lose their grounds if the fault came on the circuit they were on. IOW, this would be a moot point. See previous posts for reasons why this is not the case. The problem isn't the other AC ground also lifting. It's the signal ground wires opening due to their inability to handle the fault current. Also, if some other person (who was intending on solving the problem properly) has used a proper audio ground isolator in the signal chain at the only 'grounded' amp in the system, then we have another recipe for disaster. The probability of being electrocuted is MUCH MUCH higher than being hit by lightening. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 29, 2006 Members Share Posted December 29, 2006 Originally posted by pipedwho See previous posts for reasons why this is not the case. The problem isn't the other AC ground also lifting. It's the signal ground wires opening due to their inability to handle the fault current. Absolutely... and it does happen when a fault occurs and no solid safety ground. Also, Where, are you metering the grounds continuously during the show? If not, then an open ground would be undetected should it occur during the show. The lawyer would simply say... no at the time of the accisent you were NOT metering the ground, therfore it was an accident that you caused...$$$ Link to comment Share on other sites More sharing options...
Members where02190 Posted December 29, 2006 Members Share Posted December 29, 2006 The problem isn't the other AC ground also lifting. It's the signal ground wires opening due to their inability to handle the fault current. Once again, it it moot whether one, all or none of your amps are grounded in this situation. If a ground in the PA system suddenly is broken(which is extremely unlikely unless there is some very poor maintainence going on) then you would be the path of least resistance no matter how many of your amps are grounded. Signal ground wires are not going to be handling this, your body is. Link to comment Share on other sites More sharing options...
Guest Anonymous Posted December 29, 2006 Share Posted December 29, 2006 The tragic thing is that even debating this issue will increase the likelihood of folks trying the 99 cent solution... folks who wouldn't have ever even tought of it in the first place, let alone understand the fine differences between the wrong way, or really wrong ways to do this. How many folks who were told to leave the bridge/mono switch alone actually did? How many more folks "discovered" the bridge/mono switch by reading debates on the subject? Link to comment Share on other sites More sharing options...
Members Johnw Posted December 29, 2006 Members Share Posted December 29, 2006 Originally posted by Zeromus-X Lightning causes an average of 93 deaths and 300 injuries annually. I'd rather not take my chances! When I was doing commercial two way radio work I was in the transmitter house at the bottom of a 650 ft. tower. I had just gotten finished replacing some transmiter finals in a paging transmitter. I walked over to the door of the transmitter house to smoke a cig, when BAM. We got hit again. I picked myself up off the floor. During the next hour we took 3 more strikes, with me in the transmitter house. Not fun Even though we had everything grounded, lightning arrestors ect... we had a lot of damage. Everytime we had bad weather the tower would take hits and we would loose the paging transmitter. This was on the Gulf coast. I learned a lot about grounding there. I don't play around with grounds. The paging transmitter had 2000 volts dc on the tube at about 225 to 250 mils of current. If you treated this thing wrong I could say that you would not be around to do it again. As I have said before, I DO NOT ALLOW ANY AC GROUND LIFT DEVICES ON ANY STAGE THAT I AM RUNNING. Life is too damn short as it is without some other idiot trying to make it shorter. AC and lightning strikes can do some wierd things at times. Don't take any chances. Take Care, John Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 29, 2006 Members Share Posted December 29, 2006 Originally posted by where02190 Once again, it it moot whether one, all or none of your amps are grounded in this situation. If a ground in the PA system suddenly is broken(which is extremely unlikely unless there is some very poor maintainence going on) then you would be the path of least resistance no matter how many of your amps are grounded. Signal ground wires are not going to be handling this, your body is. You need a ground path, and generally standing on a stage in shoes is not going to allow enough current to pass to either feel or to cause injury by itself. The problem is when the user touches a solidly grounded item like a microphone housing or another grounded amp, where current can then flow directly to ground through the body from the energized guitar strings/floating ground. Link to comment Share on other sites More sharing options...
Members where02190 Posted December 29, 2006 Members Share Posted December 29, 2006 Originally posted by agedhorse You need a ground path, and generally standing on a stage in shoes is not going to allow enough current to pass to either feel or to cause injury by itself. The problem is when the user touches a solidly grounded item like a microphone housing or another grounded amp, where current can then flow directly to ground through the body from the energized guitar strings/floating ground. Absolutely correct. In order to be zapped, there needs to be a potential between the mic case and the amp. With the amps and the PA properly grounded (each with a single path to ground, through one grounded amp for instance) there is no potential. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 29, 2006 Members Share Posted December 29, 2006 Originally posted by where02190 Absolutely correct. In order to be zapped, there needs to be a potential between the mic case and the amp. With the amps and the PA properly grounded (each with a single path to ground, through one grounded amp for instance) there is no potential. And if a fault occurs on the ungrounded amps that opens the signal ground path to safety ground on the GROUNDED amp due to excessive fault current then suddenly the remaining signal ground is at line voltage potential. Now grab the mic with a sweaty hand or touch with lips and bzzzzzssst... Link to comment Share on other sites More sharing options...
Members Rick6 Posted December 29, 2006 Author Members Share Posted December 29, 2006 Another aspect of this occurs to me. Steve Vai probably uses the same, high quality amps every night. Same PA too. Lifting the ground on one of his amps clearly increases his risk. But at least he knows his equipment. My situation is that I often play on other people's amplifiers, using unfamiliar PA equipment, in unfamiliar rooms. I do occasionally play in a venue with a sound guy, but I've never seen one measure anything with a meter. The electrical risks are identical -- but the probability I might someday plug into an amp with an electrical fault is perhaps higher than Steve Vai's. So, I'm taking the advice very seriously. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 29, 2006 Members Share Posted December 29, 2006 Don't forget that Steve Vai has the best engineer in the world, and a tech that meters his grounds at all times withot fail... Link to comment Share on other sites More sharing options...
Guest Anonymous Posted December 30, 2006 Share Posted December 30, 2006 Originally posted by where02190 With the amps and the PA properly grounded (each with a single path to ground, through one grounded amp for instance) there is no potential. Dear Sir: Since neither you (nor some other seemingly interested parties) seem to be taking this issue as seriously as I think it should be taken... please explain: Do you think for an instant that the average user out there is going to understand all the intricacies of lifting grounds... and where it's ok, and where it's not? Hand a kid a 99 cent safety ground lift device, as you've recommended, and tell them this can cure a humm problem in the system... you might as well tell the young-uns to play Russian roulette to solve a humm issue. Yea... the humm might go away. You might be dead when it goes away... or maybe not... roll the dice. "with the amps and the PA properly grounded"... uh... what is it you were saying? If the system is properly grounded, there will be NO ground loop issues... and there will be none (or very minimal) humm... therefore there will be no reason to fix the problem. The reason there is a problem is because there is a problem due to something being incorrect. The offered advice is to "fix" the problem by addressing the symptom, rather than the problem. With the amps and PA properly grounded, there is no need to willy-nilly lift AC safety grounds. Where exactly is it that you suggest the AC ground be lifted in a properly grounded PA and properly grounded amps? And why would you even want to do that? With a properly grounded PA system, lifting any safety ground could only increase noise in the system. And surely you're not suggesting blindly floating grounds on an improperly grounded system? TWO WRONGS DO NOT MAKE A RIGHT... ESPECIALLY WHEN SAFETY IS CONCERNED. We seem to be living in a dark ages... where "street smarts" (spelled: superstition and wives tales) are taken seriously... particularly "99 cent solution street smarts". Link to comment Share on other sites More sharing options...
Guest Anonymous Posted December 30, 2006 Share Posted December 30, 2006 Oh yea... since there's been some name dropping here... lemme drop a few: Keith RelfLeslie HarveyJohn Rostill RIP. 99 cent solution huh? Link to comment Share on other sites More sharing options...
Members where02190 Posted December 30, 2006 Members Share Posted December 30, 2006 Correct, a properly grounded scenario, lifting one of the two amps, leaving a single path to ground, and a properly grounded sound system would have no issues. The artists previously mentioned by yours truly were examples of artists most will know by reputation who employ this method regularly. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 30, 2006 Members Share Posted December 30, 2006 Originally posted by where02190 Correct, a properly grounded scenario, lifting one of the two amps, leaving a single path to ground, and a properly grounded sound system would have no issues. The sound system isn't the problem, it's the circulating currents between the two guitar amp grounds. It would hum WITHOUT a PA. That's what the OP was dealing with and it's not uncommon which is why there are several manufacturers of proper and safe solutions. Link to comment Share on other sites More sharing options...
Members sharnrock Posted December 30, 2006 Members Share Posted December 30, 2006 My dad has a vintage vox head that shocked me the last time I used it. Faults happen all the time, and they are by no means as rare as lightning. Your entie house is grounded for a reason. If a ground fault occurs your breakers should trip, and if you really want added protection use GFCI circuits. They are way, way safer. Link to comment Share on other sites More sharing options...
Members pipedwho Posted December 30, 2006 Members Share Posted December 30, 2006 Originally posted by where02190 The artists previously mentioned by yours truly were examples of artists most will know by reputation who employ this method regularly. So you keep telling us. But, I find it hard to believe they'd be so stupid when safe solutions to the problem are available. The artists just listed by Audiopile also had disconnected grounds. Unfortunately they DIED for their troubles. And don't give me any crap about how the second amp will supply the earth through the signal ground, yadda, yadda. It is NOT failsafe and simply increases the risk of adding more names to Audiopiles list. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 30, 2006 Members Share Posted December 30, 2006 There is no shortage for stupid advice in the world or on the internet. Anyone here familiar with the Darwin Awards> Darwin Awards Link to comment Share on other sites More sharing options...
Members where02190 Posted December 30, 2006 Members Share Posted December 30, 2006 Originally posted by pipedwho The artists just listed by Audiopile also had disconnected grounds. Unfortunately they DIED for their troubles. Because they were idiots to not meter voltage between guitar and mic probably. Obviously they disconnected the WRONG grounds if it killed them. Link to comment Share on other sites More sharing options...
Members pipedwho Posted December 30, 2006 Members Share Posted December 30, 2006 Originally posted by where02190 Because they were idiots to not meter voltage between guitar and mic probably. Obviously they disconnected the WRONG grounds if it killed them. Link to comment Share on other sites More sharing options...
Members Rick6 Posted December 30, 2006 Author Members Share Posted December 30, 2006 This metering thing goes against what I think is basic principle of human nature. You never want to be in a situation where somebody has to remember to do something regularly, or else. You also want to avoid situations where everyone has to act thoughtfully, intelligently and be mistake free. You can't ignore Murphy's law. The right way to do it, is to set up a basic structure that is as close to idiot-proof as possible. That means, in this case, everything must be grounded properly. Specifically, in this case, with real heavy duty ground connections, not flimsy connections through an audio shield. Hum problems must be solved without any sacrifice in the idiotproofness of the ground connections. The idea that a stage was set up in a fundamentally wrong way and then somebody got hurt ... and then somebody else says it was the fault of the guy who was supposed to be metering things at some interval to compensate for the incorrect setup ... ugh. As far as how many famous people do it that way .. well, how many wrongs make a right? Rick Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 31, 2006 Members Share Posted December 31, 2006 Originally posted by Rick6 This metering thing goes against what I think is basic principle of human nature. You never want to be in a situation where somebody has to remember to do something regularly, or else. You also want to avoid situations where everyone has to act thoughtfully, intelligently and be mistake free. You can't ignore Murphy's law. The right way to do it, is to set up a basic structure that is as close to idiot-proof as possible. That means, in this case, everything must be grounded properly. Specifically, in this case, with real heavy duty ground connections, not flimsy connections through an audio shield. Hum problems must be solved without any sacrifice in the idiotproofness of the ground connections. The idea that a stage was set up in a fundamentally wrong way and then somebody got hurt ... and then somebody else says it was the fault of the guy who was supposed to be metering things at some interval to compensate for the incorrect setup ... ugh. As far as how many famous people do it that way .. well, how many wrongs make a right? Rick The basis of building, fire and life safety codes. Take as much of the human factor out of the equation. Not all techs are as diligent or as smart as "Where" is... Link to comment Share on other sites More sharing options...
Guest Anonymous Posted December 31, 2006 Share Posted December 31, 2006 Let's see a hand raise from all you guitarists who meter the voltage difference between your mic and your guitar strings before stepping up to the mic. Better yet, let's see a hand raise from all you guitarists who own a multimeter, or have your own personal guitar tech/ sound person who owns a multimeter. Link to comment Share on other sites More sharing options...
Members guitarharv52 Posted December 31, 2006 Members Share Posted December 31, 2006 I can't raise my hand.I use one the bass player has if I change the power tubes in my amp. Link to comment Share on other sites More sharing options...
Members where02190 Posted December 31, 2006 Members Share Posted December 31, 2006 How about a raise of hands of guitarists and bassists that, after reading this, smartened up and now not only own a meter but will do this at every gig. How about those that, before gettting their ass lit up, touch the guitar to the mic to check for any potential? While not quite the same as metering, it'll quickly let you know if there is a potential or not. Link to comment Share on other sites More sharing options...
Members agedhorse Posted December 31, 2006 Members Share Posted December 31, 2006 Originally posted by where02190 How about a raise of hands of guitarists and bassists that, after reading this, smartened up and now not only own a meter but will do this at every gig.How about those that, before gettting their ass lit up, touch the guitar to the mic to check for any potential? While not quite the same as metering, it'll quickly let you know if there is a potential or not. If the amplifier(s) are properly grounded through safety ground to earth, this will not be necessary. Link to comment Share on other sites More sharing options...
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