Microphones getting shocked by mics

[KProductions]

Hi All,....

I have an active system setup in a local venue. Tonight, - a couple of the artists reported being "shocked" by the vocal mics (beta 58's). I've had the same setup in the same location for the last 6 months and today was the first time that anybody ever reported any issue.

I have the console (Mackie VLZ 24-4) ground lifted, as are my rack, the speakers, and monitors (to eliminate hum).

The guitar amps were plugged directly into a 4 outlet surge box, - which was plugged directly into the wall (grounded)

Any suggestions...???

Thanks

 

[rroten]

When you say ground lifted, do you mean the signal ground or power ground? I must strongly insist that electrical grounds should never be lifted. NO EXCEPTIONS! I don't want to sound mean, but this is safety we're talking about. Please make sure that all of your equipment is using all 3 prongs on the electrical connectors.

Ryan

 

[DaveySimps]

Never lift the ground on your racks, or any other electrical gear. It is a serious safety concern, and strong possibility of what is causing your problem. I know it is a PITA, but find out what is causing the hum instead of taking the easy and unsafe way out of it. You system will be better for it.

~Dave

 

[Eboy87]

Never lift the electrical ground!

If you have hums and buzzes, there are other solutions that aren't life threatening. Lifting the ground on your gear is what caused the artists to get zapped. Since the gear wasn't grounded, but the amps were, the path to ground was through pin one on the mic lines, through the metal mic, across the artists' lips to their grounded amps. This is not a good thing!!!!! I cannot stress this enough, don't lift the AC ground on gear!!

 

[Erwin]

I had the same problem once.

We had nothing ground lifted. The problem seemed to be a faulty power bar. When we replaced it, the problem went away.

I have also been told that having a power conditioner for band gear can help. It is said that a badly wired guitar amp mixed with an ungrounded Mic can be lethal for a performer.

If you google shock from Microphone, you will find many horror stories, things to avoid, but no solutions. It is however, how I learned methods to get rid of performers

Seriously though, it is probably a problem with a ground connection in you system. Either the amp or the console.

 

[Eboy87]

It is said that a badly wired guitar amp mixed with an ungrounded Mic can be lethal for a performer.

As a guitar player, what happens is this. Usually these stories deal with tube amps. Voltages inside tube amps can be up to 300 volts, and if there's a problem, that goes to ground. It just so happens, the strings of a guitar are also connected ground (usually). If the ground is lifted on the amp where it's plugged into the wall, that voltage winds up on the strings, as you are now the path of least resistance to ground. And once you get close enough to a mic connected to a grounded sound system, you complete the circuit. People can (and have) die from this.

Please, throw away all ground lifts.

 

[KProductions]

thanks,... so

1. How come this just came up tonight after 6 months and many other shows...??

2. How do I eliminate the hum if I don't ground lift the system...?

All your advice is appreciated.

 

[Erwin]

1. Things have to break sometime. Ask this instead. Why not now?

2. The hum is being caused by a faulty and/or improperly installed piece of kit. It can take a lot of work to isolate it. You need to start eliminating suspects by removing them from the system one at a time.

Someone with more expertise can likely give you a good place to start. Dirty power and bad cabling would be my first guesses.

 

[dvsDave]

1) Ground everything

2) only test one variable at a time. To save time, I start with the mic and move back along the signal path.

 

[BillESC]

1. All of your gear should be grounded.

2. All audio should be on the same electrical phase.

Problem more than likely solved (unless there is a defect in one of your components.)

 

[DaveySimps]

thanks,... so

1. How come this just came up tonight after 6 months and many other shows...??

2. How do I eliminate the hum if I don't ground lift the system...?

All your advice is appreciated.

Tracing and eliminating a hum can be sort of a fine art, since there are many potential causes. I would take some time and set up each piece of gear one by one until a hum appears, and they troubleshoot each hum one at a time. Check for properly wired cables, proper cable paths (try to avoid neon lights, dimmers, etc. as much as possible). Items such as power conditioners, and isolation transformers can be great tools to help you properly rid your system of the noise. You question "How do I eliminate the hum" is sort of vague, as each situation is different. We are happy to help if we have more info such as what pieces of gear are involved and where the hum appears in the system (in a main speaker, a specific monitor, on a specific channel, etc.). We can then offer more constructive advice. It may be tedious, but it will be time well spent.

~Dave

 

[mixmaster]

thanks,... so

1. How come this just came up tonight after 6 months and many other shows...??

2. How do I eliminate the hum if I don't ground lift the system...?

All your advice is appreciated.

First take whatever you used to lift the power grounds outside and throw them away. Far away. the worlds worst invention was an appliance adapter to change a cord from 3 prong to 2 prong.

Second. Look around you. What changed in the last couple weeks? New AC service?, extra coffeepots? someone rewire a light switch? The fact that you had a hum or buzz that went away when you lifted the AC grounds, indicates a power/ground issue. First thing I would do is take a meter, or a cheap outlet tester around to every outlet and check the outlets. Ideally you should see about 118 VAC hot to neutral and hot to ground and 0 volts ground to neutral. Then check and see which outlets are on the same breaker panel. I prefer to have all my audio circuits come from a single panel as it reduces the chance of having different grounds from different panels at different parts of the system.
Third After you have established a good clean power source, plug 1 speaker into 1 amp, listen for a buzz. No buzz? add another amp and speaker (if you have one). keep adding one component at a time until you stage is wired up as usual or you get a buzz when you add a piece. If the stage is clean, plug in your snake, if the system is still clean, add your mixer. Keep going until you find the piece of gear that adds a buzz. If you find that piece, try lifting the SIGNAL GROUND NOT THE AC GROUND for that piece.
If the system is clean, when you have stage gear up, and buzzes when you add FOH, then you probably have a questionable ground in one place or another. The best solutions is to figure out which is bad and get an electrician to fix it. As a temporary fix run an extension cord from wherever your amps are plugged in to FOH for power. That should solve the problem for the evening, and prove that the buzz is caused by faulty power or ground, which will probably require an electrician to fix.
Good luck,
Matt

 

[KProductions]

Hi Guys,...

Thanks for all your knowlegable advice. I will try to setup as suggested. The main issues I see in all responses is that there is no TIME once a show is scheduled to start to trace the source of these hums, correct, and stay on schedule. Showtime is hectic enough without pulling equipment apart. I know there is no "quick fix", - which is why I utilize the ground lift adapters in the first place

I was always told that the adapters don't really "eliminate" ground but rather just change "polarity" of the equpment plugged into it. Is this not true..??

Thanks again.

 

[DaveySimps]

I was always told that the adapters don't really "eliminate" ground but rather just change "polarity" of the equpment plugged into it. Is this not true..??

Thanks again.

Absolutely not true.

~Dave

 

[rcopley]

I had an issue similar to what you are talking about only mine was the result of a bad cable and using phantom power. I had a XLR cable that was so badly insulated you could plug it into the board and hear public radio loud and clear, then when I when to touch the cable once I got a small shock, could have been static electricity, but with the condition the cable was did not want to rule out a short.

 

[howlingwolf487]

I really hope you didn't lop off the ground prongs of your AC cords...you'll have to go out and buy new ends (rated properly, of course) and put them on (not too hard, as they usually screw in place).

I second the statement that you should check to see what has changed in the environment. New lights, dimmers, appliances, etc.? Any of those things could affect your AC power.

And, once again for good measure (everybody now...):

NEVER LIFT AN AC GROUND!!!!

Okay, I think you get the point. I'll post a great article by Mr. Dave Rat when I'm able to find it...it's on PSW somewhere, I know it!

 

[Chris15]

Now to throw some confusion into things...

A Beta 57 vocal mic on a live to air television broadcast was zapping the artist's minders in early rehearsal (before the talent arrived). As best everyone can work out, the cable was fine, there were no grounds lifted, and everyone's suspicion was on a flaky technical earth in the building. We were tempted to dump a bucket of water (salty would have been better) down the pit over the technical earth stake, but ended up solving the problem otherwise. Note that in this particular setup, the direct feed to the mic was from the truck with Mons and FOH getting an isolated split. The entire audio truck was fed off the OB big mamma UPS with generator backup. ie., the show could go to air in a blackout (well lighting I suspect may have needed to swap over to their generator, not sure it was UPS backed and online though it may have been).

I think the moral in that story is that even with a professional crew who know what they are doing, sometimes there are things beyond one's control that will lead to a shocking experience. I can't remember what they ended up doing exactly for the show. They either switched the talent off her preferred B57 to a UHF-R radio mic or they threw an iso transformer in the line...

 

[waynehoskins]

The usual cause for getting zinged on a vintage tube amp has nothing to do with the "high" voltages inside, but an old technique of filtering the primary. It was common to bypass the AC mains to chassis, both sides. This effectively places the chassis halfway between neutral and hot, or 60 volts in the 117V Imperial world. What's on the other end of the microphone has its chassis (which is probably tied, at least round-about, to the chassis of the microphone) at earth, which is at neutral, 0 volts. So there's a 60 volt difference between the shell of the microphone and the pickup on the guitar. Hand hits pickup, lips hit microphone, zing!

Two safe solutions:
- Isolate the chassis of the guitar amp by removing those stupid bypass capacitors
- Earth the chassis of the amp.

300 volts high? Bah! That's nothing!
I only partly kid. I'm used to playing with 800-volt stuff, but even 300 volts can be nasty if you get across it. I've been bitten by 60 volts a ton of times, always because of those stupid bypass capacitors, and every time is no less un-fun than the last. Be careful with power, everyone.

 

[KProductions]

Wayne, - I think you hit the nail on the head. The guitarist WAS using an older tube head - and this seems to be the difference between this band and the others that have used the system.

So let me get this right. Although his "amp" was properly grounded via the three prong plug, - his amp "chassis" still needs another ground...??

Should this happen again, I'm sure the guitarist will not let us take his amp apart and remove capacitors. How do I Earth the chassis of the amp on the fly right before showtime..??

Thanks,...

 

[TimmyP1955]

1. All of your gear should be grounded.

2. All audio should be on the same electrical phase.

Problem more than likely solved (unless there is a defect in one of your components.)

1. Agreed

2. Should not make a difference so long as the grounds are all at the same potential.