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One sugar cube and off to the hospital

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Greg Fretwell
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mxslick wrote:
Take some voltage measurements from mike to a known ground on your next gig and you may be surprised.

Just the other day I had the exact same complaint from a customer of a new home I wired. They have a band and practise in the house, and apparently they are getting shocks when their lips touch the mics....would a GFCI prevent this???

Off the topic here....they are also having a hum from the bass. We have electronic dimmers throughout the house, and the homeowner has also installed quite a few compact fluorescents. Would this cause the hum?


Sixer

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and apparently they are getting shocks when their lips touch the mics....would a GFCI prevent this???
Not likely that a GFCI would see that current unless is it comming directly from the building power supply. It is most likely from the load side of a transformer or power supply in the equipment and the line side GFCI will not "see" that leakage current.
Don


Don(resqcapt19)
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Those leakage currents can still be a problem in modern gear.

Just a few days ago I was working on a home video system and got bit as I pulled out a metal-bodied coax plug while leaning on the case with my other arm. It wasn't exactly a powerful shock, but it was certainly more than a mere tingle -- enough to make me jump.

That was the combined leakage currents from two TVs, two VCRs, a DVD recorder, and a digital receiver.

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And the simple improper use of an expension cord that powers the amplifier. Was there an adapter used to defeat the EGC and a simple 2w extension cord the possibly reversing the line and neutral conductor, a defect in the EGC, broken ground EGC ground plug? All thinks that are either overlooked or disregarded by people who don't have a clue or know the importance of proper grounding. Never the less, even if all of the safety precautions were met and a GFCI outlet was used it would be in your wildest dreams that I would ever allow a wired mic be used in such a manor.
At least purchase an inexpensive cordless mic.

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A somewhat off-topic remark.

If your lips are touching the microphone head, you're not using proper miking techniques.

Ideally, your mouth should be at about a fist-length away from the mic's head.

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I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics. Consider the tingle you get when touching your tongue to a 9 volt battery. Aren't most pop screens metallic?

To check it out, I would use my Fluke on AC & DC between the contact points(body of mic/pop screen, both to flooring matl) If I saw any substantial potential, I would probably put 100kohms in parallel with my Fluke to get a handle on the source impedance. I wonder how many amps out there have their chassis ground referenced to the negative side of a bridge rectifier???

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I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics.

I was wondering when someone was going to bring that nonesense up. Answer is that's ridiculous.

Obviously the mic was hot with respect to ground or the pool was hot with respect to the grounded mic. Which and why we will probably never know.

This subject has been beaten to death both over in the Mike Holt forum and in the pro audio forums. Unfortunately this is only one of may such electrocutions caused this way.

Before anybody condems the sound system exclusively this is one instance where there could also be another cause.

These baptismals have heaters, lights and a pump. In my book that would make them a pool or spa yet I don't think they come under the applicable articles of the NEC though that might be a moot point. Keep in mind that houses of worship traditionally rely on congregants to provide the electrical and audio work.

In my opinion this is a recipe for disaster.

-Hal

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I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics.

I was wondering when someone was going to bring that nonesense up. Answer is that's ridiculous.

To expand on that information, "phantom power" is supplied to a microphone over what is known as "balanced" audio lines. On the common three-pin connector on pro mics {known as "XLR"} the power is carried on pins 2 and 3 (+) and the negative (-) is on pin 1 (the shield of the cable.) It is a DC voltage, current limited, and anywhere from 12-48 volts. (48v being the most common.)

The normal connection scheme for balanced audio mics is Pin 1 = shield; Pin 2 = "signal hot" (or +); Pin 3 = "signal return" (or -). {Note that some brands of gear reverse the signal polarity of 2 and 3}.

A "dynamic" (does not need phantom power) mic is connected between pins 2 and 3 and thus does not see any voltage across the element if the phantom is accidently left on. (Both pins are at + vDC potential).

Since the (-) end of the phantom supply is tied to pin 1 , (and thus possibly to the chassis) it would be at the same reference as the chassis and the shield of the cable, and therefore the phantom could not cause a shock as described in the thread.

And if the (+) side of phantom shorts out to shield, the supply in virtually all gear shuts down to protect itself. (That's in case a mic where pins 3 and 1 are tied together in an "unbalanced" arrangement, which obviously creates a short across the supply.)

Hal brought up a great point, that the pools have heaters, filters, lights etc. any one of which could have energized the pool.

So a properly connected mic, with a mixer or amplifier in proper working order, may have actually provided a ground path in this case.

Like Hal said, we may never know....


Stupid should be painful.
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mxslick
quote:I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics.

I was wondering when someone was going to bring that nonesense up. Answer is that's ridiculous....

I hate it when people think I'm more ridiculous than I actually am. On background, I have been Chief Engr. & Maint. Supr. of 2 major market UHF stations and part of the design / build team of a place called Beachwood Studios. I did not mean to express or imply that "phantom power" could be the cause of an electricution! In a perfect world, pastors don't get zapped and musicians don't french kiss mics. I did mean to say that I wouldn't rule out the possibility that a phantom supply could cause a tingle similar to placing your tongue on a battery.

In this case, it would still seem most like ly to me that he was the victim of a hot chassis on a transformerless PS piece of audio gear with a polarized plug. The waveform that killed him would not be a nice sine wave. On his way to Heaven, he probably experienced CROSSOVER DISTORTION!!! <Nyuk,Nyuk>

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