Good morning, again.
Had a guitarist in the other night who notified me he was getting shocked intermittently when he was at the mic - sang with lips touching the SM58 most of the time. I'm not going to say mildly shocked because that can be so very disconcerting to the performer. Any shock is too much.
This is my local haunt, and I've never had problems with shocking or noise from the AC ever before. Once notified, my actions started with checking both ends of the mixer power cord to be sure it is seated well - no problems there.
In the next song break, I swapped out the mic cable - did not really think anything would change, and I was right. I also had the guitarist flip the (I guess the polarity?) switch on his Fender amp. Nada.
I ran home and grabbed a SM57 w/foam wind screen which ''solved'' the problem through isolation by song 3.
I looked at his amp - looked to be a vintage blonde Fender - when I asked, he said it was a re-issue with the three-wire cord - I'm suspecting the ''polarity'' switch is there to make the amp ''authentic'' but doesn't really do anything.
During the break I also moved his amp plug into the same quad box the mixer, amp, and EQ were running off to equalize any possible ground potential problem that may have been between the sound system and the guitar amp. No, I did not ask him to check further. That would have been cruel.
So the show is over, and I need to check things. Of course, his rig is gone, but I can check if it is the house rig. He's not had trouble elsewhere, and if he does, he'll get his stuff checked. That aside, I did notice a tiny shock or two between the mixer face and my fingers on a different day - the first time I thought may have been static, but I'm not so sure...
Now, we have about four outlets serving the stage - I do not know whether they are on the same circuit or not.
I'm guessing I would be looking for any stray voltage on ground. I'd meter and should get:
h-n = ~120
h-g = ~120
g-n = zero
Also if I'm checking multiple outlets, any n-n, g-n, or g-g should be zero, as well. h-h would read 0 or ~240, depending.
I would check all mic cables to ensure pin-1-chassis ground is NOT connected (I did find some older cables connected this way, and took them out of service until I can rewire them).
Check any and all instrument cables...
Check power cords to mixer, amp, and EQ...
I'm guessing a decent multimeter should do the job.
Now to the questionable stuff...
There are a number of ''cheap'' power strips on stage, plus one rack-mount ''power conditioner'' serving the entire PA.
I'm guessing that a leaking, failing MOV in any of those devices could be the problem. I'm guessing I should test them for continuity/isolation between the h-n-g. Would it be right for me to expect infinite resistance, or would a couple mega-ohms be more consistent with a MOV...
I'm also guessing that those cheapies are not really appropriate for the stage, and I should get rid of them, or at least cut the MOVs out of them. I have read previous posts about the limited life of MOVs and the potential for catastrophic failure.
Is there anything I should check on the electronics? They are all 1.5 yrs old... Amp and EQ have had 10 insertions on their connectors, max, so I doubt there would be any problem with the input/output connectors. Mixer shows no physical signs of wear or abuse.
The only thing left out are the mics - I don't have a clue as to how to test them, or what to look for - or if I should check them at all.
Would a ground-fault interrupter trip if voltage is found on ground? Would that be a reasonable ''Canary in the coal mine'' test for a problem?
So my question: Am I on the right troubleshooting track? Am I missing anything?
thanks
frank
Had a guitarist in the other night who notified me he was getting shocked intermittently when he was at the mic - sang with lips touching the SM58 most of the time. I'm not going to say mildly shocked because that can be so very disconcerting to the performer. Any shock is too much.
This is my local haunt, and I've never had problems with shocking or noise from the AC ever before. Once notified, my actions started with checking both ends of the mixer power cord to be sure it is seated well - no problems there.
In the next song break, I swapped out the mic cable - did not really think anything would change, and I was right. I also had the guitarist flip the (I guess the polarity?) switch on his Fender amp. Nada.
I ran home and grabbed a SM57 w/foam wind screen which ''solved'' the problem through isolation by song 3.
I looked at his amp - looked to be a vintage blonde Fender - when I asked, he said it was a re-issue with the three-wire cord - I'm suspecting the ''polarity'' switch is there to make the amp ''authentic'' but doesn't really do anything.
During the break I also moved his amp plug into the same quad box the mixer, amp, and EQ were running off to equalize any possible ground potential problem that may have been between the sound system and the guitar amp. No, I did not ask him to check further. That would have been cruel.
So the show is over, and I need to check things. Of course, his rig is gone, but I can check if it is the house rig. He's not had trouble elsewhere, and if he does, he'll get his stuff checked. That aside, I did notice a tiny shock or two between the mixer face and my fingers on a different day - the first time I thought may have been static, but I'm not so sure...
Now, we have about four outlets serving the stage - I do not know whether they are on the same circuit or not.
I'm guessing I would be looking for any stray voltage on ground. I'd meter and should get:
h-n = ~120
h-g = ~120
g-n = zero
Also if I'm checking multiple outlets, any n-n, g-n, or g-g should be zero, as well. h-h would read 0 or ~240, depending.
I would check all mic cables to ensure pin-1-chassis ground is NOT connected (I did find some older cables connected this way, and took them out of service until I can rewire them).
Check any and all instrument cables...
Check power cords to mixer, amp, and EQ...
I'm guessing a decent multimeter should do the job.
Now to the questionable stuff...
There are a number of ''cheap'' power strips on stage, plus one rack-mount ''power conditioner'' serving the entire PA.
I'm guessing that a leaking, failing MOV in any of those devices could be the problem. I'm guessing I should test them for continuity/isolation between the h-n-g. Would it be right for me to expect infinite resistance, or would a couple mega-ohms be more consistent with a MOV...
I'm also guessing that those cheapies are not really appropriate for the stage, and I should get rid of them, or at least cut the MOVs out of them. I have read previous posts about the limited life of MOVs and the potential for catastrophic failure.
Is there anything I should check on the electronics? They are all 1.5 yrs old... Amp and EQ have had 10 insertions on their connectors, max, so I doubt there would be any problem with the input/output connectors. Mixer shows no physical signs of wear or abuse.
The only thing left out are the mics - I don't have a clue as to how to test them, or what to look for - or if I should check them at all.
Would a ground-fault interrupter trip if voltage is found on ground? Would that be a reasonable ''Canary in the coal mine'' test for a problem?
So my question: Am I on the right troubleshooting track? Am I missing anything?
thanks
frank