Members LORDGOREKKK Posted March 17, 2007 Members Share Posted March 17, 2007 how do you prevent the annoying feedback that is created when a laptop is near a PA setup? Link to comment Share on other sites More sharing options...
Members dboomer Posted March 17, 2007 Members Share Posted March 17, 2007 shut off your mic and speaker in the laptop Link to comment Share on other sites More sharing options...
Members Zeromus-X Posted March 17, 2007 Members Share Posted March 17, 2007 We can't run our laptop through the PA unless we're using a ground lift on the AC adapter for the laptop. Otherwise we get a horrible ground hum. We just use it for playing MP3s between the sets, but it's an old laptop so the battery won't last the entire gig if it's not plugged in. Link to comment Share on other sites More sharing options...
Members dboomer Posted March 17, 2007 Members Share Posted March 17, 2007 You shouldn't be using a ground lift on the AC ... you should be using a transformer 1:1 interface for safety. Link to comment Share on other sites More sharing options...
Members Zeromus-X Posted March 17, 2007 Members Share Posted March 17, 2007 Yeah, we should be. But we probably should also not be plugging 4500W worth of gear into the single AC outlet by the stage; we probably shouldn't be using an unbalanced XLR setup; we probably shouldn't be playing underneath TVs that are held to the ceilings with bungee cords. And I'm sure a lot of other worse things. Sometimes at {censored}ty venues you take what you're given and get out when you can. I know there have been tons of arguments concerning $0.50 ground lift adapters, and I can see the point when dealing with massive amounts of power. But plugged into a laptop AC adapter... don't see an issue. Hell, my laptop uses a 2-prong plug anyway... but his uses a 3, and that's where the music is. Convince me that a laptop with a ground lift is a public safety hazard and I'll convince him to change his ways. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted March 17, 2007 Members Share Posted March 17, 2007 Convince me that a laptop with a ground lift is a public safety hazard and I'll convince him to change his ways. The world is not a safe place, but we attempt to minimize man made hazards. Safety isn't only about not doing something 'cause if you do somebody's gonna get hurt. Safety is also about stacking the odds in your favor so there is virtually no chance of somebody getting hurt if what shouldn't go wrong does go wrong, and at the worst possible time. Typically a 3 prong 110V AC cord is that way because there's a good chance that if something goes wrong with the gadget, live AC could exist on a touchable surface of the device, or some device attached to the defective device. The safety ground is there so if the hot leg of the AC gets somehow loose, it will short out against the safety grounded chassis (and trip the breaker)... however, if the safety ground for the chassis has been defeated, then there's a possibility the path to ground could be through somebody's body. And... it's not about how much current the device can draw... it's about how much current the AC source can deliver... which is typically 20A of 117V with a common commercial Edison outlet. 20A of 117V is plenty enough to bring on a very long dirt nap. If you need to lift the ground on your laptop to eliminate a nasty humm, then either source a double insulated 2 prong AC power supply for the laptop, or get the 1:1 AC isolation transformer like Don suggests, then plug in and play with confidence. See... when there's a disaster and somebody gets hurt (or killed) it's rarely because of one factor, generally there's a perfect storm of contributing factors... and if any one of the contributing factors didn't exist, the disaster wouldn't have happened. Eliminating all the KNOWN possibilities stacks the cards in your favor so that the unknown possibilities don't have a completed chain to feed on. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 17, 2007 Members Share Posted March 17, 2007 I know there have been tons of arguments concerning $0.50 ground lift adapters, and I can see the point when dealing with massive amounts of power. But plugged into a laptop AC adapter... don't see an issue. Hell, my laptop uses a 2-prong plug anyway... but his uses a 3, and that's where the music is.Convince me that a laptop with a ground lift is a public safety hazard and I'll convince him to change his ways. Only 10mA is all that is required for death... this is current flow due to voltage and has nothing to do with "massive amounts of power". If your laptop is factor equipped as an ungrounded device, it uses a different type of construction (for safety reasons) in the power supply in order to qualify for UL listing. Link to comment Share on other sites More sharing options...
Members bigmike216 Posted March 17, 2007 Members Share Posted March 17, 2007 A ground lift on the DI's will do the same thing. No more noise. Link to comment Share on other sites More sharing options...
Members Prog Posted March 17, 2007 Members Share Posted March 17, 2007 Convince me that a laptop with a ground lift is a public safety hazard and I'll convince him to change his ways. I can't do it. Especially since the AC never gets past the plastic line lump. It's less dangerous than using a table lamp (of which will probably require 30 years of experience and a BSEE by the time this thread is finished ). Lift it. The new James Bond would. Oh, and no smoking. Wear a seatbelt. Stay off the junglejim. No Lawn Darts. Eat yogurt. And no trans-fat. Always be ascared. Link to comment Share on other sites More sharing options...
Members Not Serial Posted March 17, 2007 Members Share Posted March 17, 2007 a double insulated 2 prong AC power supply you mean a double jacketed supply :D Link to comment Share on other sites More sharing options...
Members Not Serial Posted March 17, 2007 Members Share Posted March 17, 2007 i duuno. theres a lot of ac in that laptop. the inverter that powers the lcd has a few volts to it, dont know if it would kill ya or not though. i've never had an issue hooking up a laptop to a pa through my peavey 10/4. works everytime. Link to comment Share on other sites More sharing options...
Members W. M. Hellinger Posted March 17, 2007 Members Share Posted March 17, 2007 Lift it. The new James Bond would. Correct me if I'm wrong, but concerning James Bond: 1) He's a fictional character. 2) He repeatedly cheats death... against seemingly incredible odds. 3) He understand (knows) a lot about a lot of stuff. 4) He's got a stunt double to do the dangerous stuff. One of my favorite "redneck lines": Famous redneck last words: "Hey ya-all, watch this..." More famous last words: "Relax... this isn't dangerous, I've seen it done before." Link to comment Share on other sites More sharing options...
Members flanc Posted March 17, 2007 Members Share Posted March 17, 2007 I'm not as smart as James Bond...or as good looking. Ok...I'm starting to get kinda bummed here. Oh well...back on topic. Since I'm not smart as James Bond...here is where I was originally going with this! I'd just play it safe and get a couple of these 1:1 RCA Isolation transformers: http://www.computercablestore.com/detail.aspx?ID=7988 or go to radioshack and get an 1/8" stereo to 1/4" (L and R) cable and just use a couple direct boxes. It shouldn't be an expensive project. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 17, 2007 Members Share Posted March 17, 2007 Especially since the AC never gets past the plastic line lump. Not true. In a SMPS line lump failure, 120 volts can indeed pass through and the only thing that would protect you AND the equipment you attach to it is the safety ground reference. It's not the plastic line lump issue, it's 120 volts passing through the copper conductors and connecting with the computer housing itself. Link to comment Share on other sites More sharing options...
Members Not Serial Posted March 17, 2007 Members Share Posted March 17, 2007 i have 3 peavey 31 band eqs, not bad eqs either (i like them better than a certain brand of eq....) i use them on wedges. none of them came with ground pins on the power cable. do they still do that? these are around 10 years old or so, i bought them new. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 17, 2007 Members Share Posted March 17, 2007 i have 3 peavey 31 band eqs, not bad eqs either (i like them better than a certain brand of eq....) i use them on wedges. none of them came with ground pins on the power cable. do they still do that? these are around 10 years old or so, i bought them new. Equipment can still be built safely and UL listed, but require different construction techniques to eliminate the AC ground pins. Link to comment Share on other sites More sharing options...
Members Dogoth Posted March 18, 2007 Members Share Posted March 18, 2007 or go to radioshack and get an 1/8" stereo to 1/4" (L and R) cable and just use a couple direct boxes. There's a good chance that a Direct box won't do the trick. If the noise is higher frequence buzz (as compared to a 60 hz bass note) then it's probably electrostatic noise getting in through the cheap switching powersupplies that are sold with virtualy all laptops (some cheap ones just seem to filter this out a bit better than others). I wish I could tell you a mfgr that specificaly makes better notebook supplies but cant. I do know that (from years of A/V work) about 1 in 10 laptops have this problem. The only SAFE cure I know of is buying a new supply (I had this problem and this action cured it). I bought it from a local retailer who would let me return it if It didn't fix the problem. I think I just got lucky. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 18, 2007 Members Share Posted March 18, 2007 Generally the direct box and lifting pin 1 will work. The reason for the noise is due to the return currents from the SMPS filters being dumped to ground and some of it takes the audiio ground as the return path, contaminating the audio signal. Link to comment Share on other sites More sharing options...
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