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In Reply to: Re: Grounding 101 posted by MicKilla on September 01, 2003 at 21:17:49:
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?
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.
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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.
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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.
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Good idea about the clubs outlets. I'm going to bring that up about having something in my bands contracts about it. Thanks.
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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.
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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