3guk Posted March 2, 2006 Share Posted March 2, 2006 Hi Guys, Our college has just set up a relativly new large sound system and we are having a problem with a Hum in the Monitors speakers on stage. It seems to be a 60hz sound and hence I am assuming it could be a ground loop. Would a product like a s ground loop isolator fix this kind of problem. We think the monitors and desk are on different mains circuits within the theater. Link to comment Share on other sites More sharing options...
Brian Posted March 2, 2006 Share Posted March 2, 2006 It seems to be a 60hz sound and hence I am assuming it could be a ground loop.50Hz in the UKWould a product like a ground loop isolator fix this kind of problem.Possibly but it's better to fix the problem at source.We think the monitors and desk are on different mains circuits within the theater.As long as all your audio lines are balanced then you won't have a problem. It's humming because somewhere you have a signal line tied to earth. Find that and the hum will vanish. Link to comment Share on other sites More sharing options...
3guk Posted March 2, 2006 Author Share Posted March 2, 2006 How would you suggest I fix this problem ? Sorry for all the questions, I have never really had a problem like this before as we haven't had monitors to use. Another technician tried using an Active DI box in between the Multicore on stage and the Monitors and that did nothing even when the ground lift switch was flicked. How could I solve it ? Edit !! Right, I have still been fiddling and removing the ground from the XLR on the stage does nothing the hum still remains. If the earth is temporarily disconnected from the active monitor then the hum goes. Since doing this is illegal its not a solution I just wanted to tell you guys incase it helped with the diagnosis ?! The signal path is like so Board Aux Out --- Jack To XLR---- XLR Multicore---- XLR To Jack----- Jack into the Monitor Line Input. Thanks Link to comment Share on other sites More sharing options...
Brian Posted March 2, 2006 Share Posted March 2, 2006 How would you suggest I fix this problem ?Well I have a very reasonable daily rate :) How could I solve it ?We're going to need a lot more info...Where are your amps? What type are they? What feeds the monitor amps? And where is that? What type of cable runs between the two? What connectors has that got on it? Link to comment Share on other sites More sharing options...
3guk Posted March 2, 2006 Author Share Posted March 2, 2006 I just updated my post with a bit more info. The monitors are made by LEM and are active. They are fed from an AUX from a soundcraft Live8 board. Link to comment Share on other sites More sharing options...
MarkPAman Posted March 2, 2006 Share Posted March 2, 2006 The signal path is like so Board Aux Out --- Jack To XLR---- XLR Multicore---- XLR To Jack----- Jack into the Monitor Line Input. Are the XLR to Jack & Jack to XLR leads balanced & correctly wired?They should be:pin 1 to sleeve pin 2 to tippin 3 to ring Link to comment Share on other sites More sharing options...
Simon Lewis Posted March 2, 2006 Share Posted March 2, 2006 You should be running the whole rig from one mains distribution system. Although running the whole system 'balanced' should reduce mains hum etc., there is plenty of equipment out there that does not comply with the correct internal wiring standard needed to deal with mains earth currents safely and quietly. Link to comment Share on other sites More sharing options...
3guk Posted March 2, 2006 Author Share Posted March 2, 2006 Mark should the leads be stereo, we were using mono leads for this exercise purely because they only need a mono mix. Simon, Im not entirely sure as to the wiring of the place, its on the colleges list of places to re-wire and from having a peek the wiring seems to be all over the place. The speakers do not hum when not connected to a signal. Link to comment Share on other sites More sharing options...
Brian Posted March 2, 2006 Share Posted March 2, 2006 Mark should the leads be stereo, we were using mono leads for this exercise purely because they only need a mono mix.Not so much stereo but using 'stereo' jacks - Yes. Link to comment Share on other sites More sharing options...
MarkPAman Posted March 2, 2006 Share Posted March 2, 2006 Mark should the leads be stereo, we were using mono leads for this exercise purely because they only need a mono mix. Yes (sort of), but it is for a balanced signal not left & right.As in a standard mic lead pin one will be 0V, pin 2 will be hot, that's the signal, pin 3 will be cold, that's the exact opposite of the signal.That's how it will leave the desk. Then if there is any interference added in the multicore (like a 50 Hz hum) it should do the same thing to both hot & cold signals. The amp in your monitor will the work on the difference between hot & cold so not "see" the interference. Simon also has a point about the mains, get somebody qualified to check the electrics for you, especially that you are on only one phase. Link to comment Share on other sites More sharing options...
Tomo Posted March 2, 2006 Share Posted March 2, 2006 Mark should the leads be stereo, we were using mono leads for this exercise purely because they only need a mono mix.Ok, you're very confused about stereo, mono and balanced. A normal XLR connector is actually mono, even though it has 3 conductors.For maximum signal quality and minimum interference, they should be balanced - this means that it has a mono signal going down two wires, and a screen. What matters is the difference between the two wires, not the actual levels on either wire compared to the screen or to Earth - this creates your sound.The two wires are twisted together to make them as close to each other as possible, and the theory is that any interference will be the same on both wires - if one goes up by 1v, the other does as well, so the difference between them is unchanged. The screen acts as an overall shield against interference, as if it gets too large Bad Things Happen. Stereo is achieved by sending two different signals - over XLR you would send two different cables.TRS jacks confuse the issue by being either Stereo or Balanced, depending on the equipment. As to solving the problem - find what creates the hum. Mute EVERYTHING at the desk - is the hum still there?If so, the fault is between the desk and the speakers.If not, gradually unmute each channel until it starts. Once you have the location, the solution can be found. Link to comment Share on other sites More sharing options...
Bobbsy Posted March 2, 2006 Share Posted March 2, 2006 Mark should the leads be stereo, we were using mono leads for this exercise purely because they only need a mono mix.Not so much stereo but using 'stereo' jacks - Yes. Er...are the Aux outs on the Live 8 balanced though? In the back of my mind I have a hunch they're not and a quick look at the block diagram on the Soundcraft site seems to support this, though elsewhere in the online manual it implies otherwise. Bob Link to comment Share on other sites More sharing options...
smidge Posted March 8, 2006 Share Posted March 8, 2006 Although this might have been the first thing someone would try, but it's kind of obvious but can be over looked. I was working with active Meyer monitors a few weeks ago, and we got an earth hum. The problem turned out to be the 13A extension cable providing power to the wedges. This has a bad earth connection. Replacing the extension fixed the problem. Good luck solving your problem, it's an annoying one. Link to comment Share on other sites More sharing options...
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