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In Reply to: Grounding 101 posted by Bill Fitzmaurice on September 01, 2003 at 13:59:42:
Phew, that's quite a read. That's all well and good, but in practical terms how would i go about figuring out which component is causing the problem?
If it is indeed an electret, the effect can be from the polarizing voltage on the mic grid.
no, it's a SM58. Can phantom power really affect whether the mic can cause shock to the singer?
was electricuted to death on stage, by his mic. I don't know if it was an electret or dynamic.
Especially if the cable is mis-wired, or the mic is damaged.
phantom puts a voltage into pins 2 and 3; if you have a mis-wired cord one of those voltage sources could end up in the mic body. Usually that would cause a lot of noise and probably fry the mic element as well but it's not impossible for a mic as pyhsically tough as a 58 to stand up to the voltage and serve as a veritable lightning rod as far as the vocalist is concerned.
Obviously there is something wrong at the component that the microphone plugs into, but beyond that all of the components of your system, amps, mixer, effects rack, whatever, have to be properly grounded and interconnected. If not you will at best suffer from a lot of noise and poor sound; at worst you'll go through singers like Spinal Tap went through drummers. It's not a matter of 'fixing' one component- it's a matter of making sure all your gear is properly hooked up. Once you're sure the grounding is OK from a power standpoint then you need to get the signal grounds in order- see RaneNote 110 Sound System Interconnection. Is it a big job? Yes. Worth the effort? It's why musicians and actors wait on tables but audio engineers are never unemployed.
Tell us about your sound system and how things are hooked up and we might be able to give you a more detailed answer.One thing is obvious, there's a potential where there shouldn't be.
Is your sound system grounded?
Have the third prongs been snapped off of your electrical cords so you can plug into two-prong outlets?
It really sounds like your electrical ground is floating.
All the components should be properly grounded. The mic is directly connected to a mackie mixer. The mixer and all signal processors have 3 prong connectors and are connected to a furman power conditioner that's connected to the electrical outlet. The signal outputs are then connected to powered speakers that all have 3 prong connectors.
I've heard of electric guitarist getting shocked on the mic 'cuz of faulty amps, but my singer plays acoustic through a direct box that's connected to the same mixer.
Is the outlet really grounded?The tester Bill mentioned has three indicator lamps that when lit in certain combinations will tell you about outlet you're plugging into.
But, even if there is a ground wire running from the outlet to the distro box and the indicator shows a ground, it doesn't mean that the ground is at zero potential.Try these two things:
1-test the mic on the singer with phantom both on and off. If no difference, then try a different mic and cable. If this doesn't work, then:
2-ground strap the Furman (run a wire from it's metal case) to a metal pipe that comes out of the ground, a steel beam in a steel frame building, rebar sticking up out of concrete, or any suitable earthing connection you can find. If this eliminates the problem, the building you're in has an electrical grounding issue. Play there at your own risk.
Note: Beware when connecting the strap. If you see any sparking, pack up your gear and split. Also, if strapping does eliminate the problem, don't be tempted to leave it in place. The building's electrical system would be earthed through your gear, and I doubt that you want your gear to get damaged or destroyed.
Having a 3 pin outlet is no guarantee that the third pin is actually connected to anything. Go to Rat Shack for a tester that will plug into an outlet and identify via LEDs any circuit faults. Then threaten to sue any club with deficient power supply.
The direct box could also be at fault. The better ones have a ground lift switch so that you can ground or de-ground the chassis. To be sure it's not AFU use a voltmeter to read AC voltage from the guitar strings to the mic body. There shouldn't be any.
Good idea about the clubs outlets. I'm going to bring that up about having something in my bands contracts about it. Thanks.
An additional factor, are the mixer power and the stage power ,that the guitar amp is plugged into, on the same breaker panel.
power feeds from different panels may have different ground potentials. All grounds are not created equal.Lee Salter
While that can have an impact, the more important question to ask is, "Are they on the same phase?"When multiple pieces of interconnected gear are plugged into outlet circuits with different phases, interchassis currents will occur. Often, people assume that the resulting hum is from a "ground loop", and they start lifting grounds until they finally find the one that stops the hum. By this point, the whole system is usually floating, which makes for a shock hazard.
When you do have multiple pieces of gear plugged into different outlet circuits, make sure that they are all on the same phase. If you have 240v single phase service, this would be every other breaker. If you have 3-phase service, this would be every third breaker. If you have fuses, or some older distribution system, then who knows.
One thing that you can do is to run an extension cord from one place where gear is plugged in to wherever else you'll have gear plugged in. Use a voltmeter and test between the hot leads of the extension cord and the wall outlet. If your outlets are wired correctly, this would be the smaller of the two slots. If you measure 0 volts, then the outlets are the same phase. If you measure 208 or 240 volts, then the outlets are on differing phases. Either find another outlet with matching phase, or if you know what you are doing, swap some wires in the distribution panel.
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