Idea for a simple box that prevents microphone shocks, reasonable?

[Processaurus]

If I understand it correctly, the shocks you can get from a mic while playing guitar, with both the PA and your amp being 3 prong (not some crusty suicidal 2 prong mojo ridden tube amp), are from a difference in ground potential between the outlet the PA is plugged into and your amp's outlet, so when your lips touch the mic, your body completes a circuit from the mic grounded through the PA outlet to your hands on the guitar strings that are grounded through the amp outlet, causing a DC current through you.

I'm wondering if this could be fixed in a safe, noiseless way, by taking your body out of the circuit by shorting that connection that was being made with your sadly conductive lips.  How about a box with an XLR in and out, that are wired straight through, but with a big long zip cord, connected to ground in the box and xlr jacks, that has a banana plug soldered on the free end, that can plug into the third prong hole (safety ground) in the outlet back by your amp.  Or maybe just a big alligator clip hooked to ground on your pedalboard, that can clip on the metal part of the xlr cord as it plugs into the mic, or the snake.  Would it make stuff hum like crazy having current from the mystery difference in ground potential from the two outlets going through the wire? sparks?

Or would it be better to lift the ground on the xlr to the PA, so the mic is only grounded back by your amp (or to your pedalboard or guitar cord somehow).  Idea II would be a box that had an XLR mic in, XLR PA out, and a 1/4" guitar in and out.  Everything is wired straight through, but the ground is lifted on the PA XLR connection.  Mic is grounded along with your guitar through your amp.

[jlullo]

i would greatly be interested in this.  that is pretty much the worst thing on earth when it happens.  i always wanted to invent a microphone with a ground lift switch so it could be taken care of on the fly....

[soulsonic]

Two words: Isolation Transformer.

[wampcat1]

I just use a thick foam screen cover on my mic.

[jrc4558]

At this website: http://www.guitarnuts.com/index.php
is a good description of a way to deal with similar problem on guitars. Maybe something similar with mics?

[gez]

I think it was Craig Anderson's book that mentioned Dan Armstrong's solution to this problem: interupt the ground-wire connected to your guitar's bridge and reconnect via a cap (with suitable rating).  The cap blocks DC, so no shock.

Alternatively, remove the wire alltogether and follow Donald Brosnac's instructions on total shielding to prevent guitar hum:

http://www.amazon.com/Guitar-Electronics-Musicians-Reference/dp/0711902321

I used to have a US amp with only 2 prongs.  I was too lazy to wire it up to a three pin plug and both my brother and myself used to get routinely shocked...ah, those were the days! 

[aron]

Have you guys tried that cap or cap+resistor mod? I did and I couldn't stop the noise. It was terrible, but maybe my guitar wasn't shielded enough.

[Pushtone]

I just use a thick foam screen cover on my mic.

Yes a Foam windscreen would be the simplest solution.

Yes a box that does isolation could be a last ditch save,
Radial, the Tonebone guys, make this in a product call an SGI.
And I think Jensen Transformer has the schematic on their site.


But lets not forget the RIGHT way to power the stage and PA.

You need an AC distro system that connects all stage gear and the PA to either a stove plug or 3-phase power source.
There would be no ground potential shock then. At least I've never gotten a complaint.

Its very easy to build your own smallish distro. It's really just a few junction boxes mounted to a plywood board.
There are some construction tricks, like route a handle in the plywood, or hinge two boards together for an "A-frame" design that stands up.

Most likely the bars you play will have a 30 amp "stove plug" available.
Connect the distro to the stove plug with, perhaps 75' of feeder cable.
The distro has the breakers and separate U-ground outlets. I typically drop a quad box at each station, drums/bass/guitar etc.
each quad box connects to the distro with a home-run extension. Typical stage needs two, three 15amp circuits at most.
A couple more 15amp circuits for the PA amps, more if you need it. Some like to use 30amp twist lock connector to take two circuits over one SJOW cable and break it out into two circuit quad boxes inside the amp racks.
Finally the FOH system gets one 15amp circuit on a U-ground and connects with 100' extension cable to a quad box. The 100' AC line is loomed to the main 24 channel mic-snake.

That's the right power

[soulsonic]

Most likely the bars you play will have a 30 amp "stove plug" available.
Connect the distro to the stove plug with, perhaps 75' of feeder cable.
The distro has the breakers and separate U-ground outlets. I typically drop a quad box at each station, drums/bass/guitar etc.
each quad box connects to the distro with a home-run extension. Typical stage needs two, three 15amp circuits at most.
A couple more 15amp circuits for the PA amps, more if you need it. Some like to use 30amp twist lock connector to take two circuits over one SJOW cable and break it out into two circuit quad boxes inside the amp racks.
Finally the FOH system gets one 15amp circuit on a U-ground and connects with 100' extension cable to a quad box. The 100' AC line is loomed to the main 24 channel mic-snake.
That's the right power

Not the bars I play in..... I'm usually lucky to even get a functioning outlet! Distros are cool when you have the power available for them, but most places that don't already have all that stuff already set up usually won't have the ability to do one. You're talking about real professional kind of setups, and while that's certainly what I prefer, I hardly ever find that in reality. Usually it's a struggle not to have the PA be a humming mess or have it blow breakers one minute into the first song. Do you live in Indiana? - maybe I could hire you to be my sound guy - I could sure use someone who has a clue.

Have you guys tried that cap or cap+resistor mod? I did and I couldn't stop the noise. It was terrible, but maybe my guitar wasn't shielded enough.

I've had exactly the same problem whenever I tried it. Proper grounding and/or the use of isolation transformers is the ONLY way to effectively deal with shocks and ground hums. I wish there was other ways, but there isn't. I've tried every alternative, idea you could think of, and none of them work effectively. You don't have to buy an $80 Jensen xfrmr or a $300 Radial box..... Edcor makes some excellent iso xfrmrs.
This one looks good for mics: http://www.edcorusa.com/products/transformers/mx/mx1cs.html
This one looks good for guitars:  http://www.edcorusa.com/products/transformers/wsm/wsm15k-15k.html
You could just look up the papers on the Jensen website for suggested iso circuits and just use the more affordable Edcor xfrmrs with the same specs.

[Paul Marossy]

Isn't the ground lift on a DI box supposed to eliminate a path to ground so that shock can't happen?

[Pushtone]

Isn't the ground lift on a DI box supposed to eliminate a path to ground so that shock can't happen?

Yes. That what it does. But there isn't a place for a DI in this senario.
The isolation has to be between the guitar and the amp, or between the vocal mic and PA console.

Those less expensive X-formers look very good.

The E guitar will not benifit that much from a Jensen x-former like a bass or acoustic would.

[Sir H C]

Switchcraft (and I assume others) make an XLR to XLR with an isolation transformer in it.  That worked in the past for live sound.  Still it was always a poorly grounded amp.  To see where the problem is, bring a voltmeter with you and see where the voltage is by putting it on the AC volts scale and touch one side to the ball of the mic, and hold the other end, less than a volt, cool.  Do the same with the amp touching the shield of the input cable, often you will see 60+ volts for some old amps with polarity reverse. 

[wampcat1]

Most likely the bars you play will have a 30 amp "stove plug" available.
Connect the distro to the stove plug with, perhaps 75' of feeder cable.
The distro has the breakers and separate U-ground outlets. I typically drop a quad box at each station, drums/bass/guitar etc.
each quad box connects to the distro with a home-run extension. Typical stage needs two, three 15amp circuits at most.
A couple more 15amp circuits for the PA amps, more if you need it. Some like to use 30amp twist lock connector to take two circuits over one SJOW cable and break it out into two circuit quad boxes inside the amp racks.
Finally the FOH system gets one 15amp circuit on a U-ground and connects with 100' extension cable to a quad box. The 100' AC line is loomed to the main 24 channel mic-snake.
That's the right power

Not the bars I play in..... I'm usually lucky to even get a functioning outlet! Distros are cool when you have the power available for them, but most places that don't already have all that stuff already set up usually won't have the ability to do one. You're talking about real professional kind of setups, and while that's certainly what I prefer, I hardly ever find that in reality. Usually it's a struggle not to have the PA be a humming mess or have it blow breakers one minute into the first song. Do you live in Indiana? - maybe I could hire you to be my sound guy - I could sure use someone who has a clue.

Have you guys tried that cap or cap+resistor mod? I did and I couldn't stop the noise. It was terrible, but maybe my guitar wasn't shielded enough.

I've had exactly the same problem whenever I tried it. Proper grounding and/or the use of isolation transformers is the ONLY way to effectively deal with shocks and ground hums. I wish there was other ways, but there isn't. I've tried every alternative, idea you could think of, and none of them work effectively. You don't have to buy an $80 Jensen xfrmr or a $300 Radial box..... Edcor makes some excellent iso xfrmrs.
This one looks good for mics: http://www.edcorusa.com/products/transformers/mx/mx1cs.html
This one looks good for guitars:  http://www.edcorusa.com/products/transformers/wsm/wsm15k-15k.html
You could just look up the papers on the Jensen website for suggested iso circuits and just use the more affordable Edcor xfrmrs with the same specs.

I was just agreeing with you and noticed we both live in Indiana... we must play the same type of bars! 
I can count on one hand the number of times we've had an excellent source of elec... the warmer months are full of outside stuff so it's normal for us to be running off of a generator. It's quite normal for our clubs here to have electricity that was wired up by the bar owner's cousin or something... a local bar in Mooresville (used to be joe's grill) had all 10 amp breakers anywhere close to the stage and we would commonly kick the breaker at least once per set.

[Pushtone]

India! This forum never ends at blowing my mind.
Whats a typical set list in India? Different worlds...


Look, if the bar has an electric stove it has a 30 amp stove plug.
Its usually not that they don't have one but that it's far away in the back of the kitchen.
An important part of any AC distro is the feeder cable from the stove plug to the distro board.
75 feet of SJOW feeder cable is heavy and needs it's own case/dolly
This is where it breaks down for the working band.

And this is where the foam windscreen starts to looks good.

[soulsonic]

INDIANA - not India!
Indiana is a state in the Midwestern area of the United States. Our capital is Indianapolis. John Mellencamp and Charles Manson are from here.
I think Brian and I would have a better chance of finding a good sound system setup if we DID live in India. And at least India has some real culture to it!
Ever see the movie Blues Brothers with John Belushi? You know the scene where they play at "Bob's Country Bunker"? That's supposed to be Kokomo. That's where I live. It's even worse than how it's portrayed in the film, though not necessarily in any way the involves country music.

I've gotten OK sound at some of the places in Indianapolis. We played at Zanies Too last month and the sound wasn't bad. We're playing there again next month, so you should come check it out Brian! The sound at Birdie's is decent too. Their sound guy really liked my amp! Sound at the Emerson pretty much sucks.

But as far as running a power cable for a distro from the kitchen of the bar, the chances of the bosses allowing you to do that around here are slim to none. There are some very strict ordinances about running mains cabling all over the place like that. And if you don't have a licensed & bonded electrician doing it for you, you're pretty much out of luck.
Pushtone, I know this may sound strange, but there are parts of the U.S. where the quality of life and the level of modernization are below Third World status. I mean this literally and without exaggeration. I can show you neighborhoods where you'd swear you were in a bombed-out warzone, and towns where you wonder if they even have electricity or running water.

[wampcat1]

INDIANA - not India!
Indiana is a state in the Midwestern area of the United States. Our capital is Indianapolis. John Mellencamp and Charles Manson are from here.
I think Brian and I would have a better chance of finding a good sound system setup if we DID live in India. And at least India has some real culture to it!
Ever see the movie Blues Brothers with John Belushi? You know the scene where they play at "Bob's Country Bunker"? That's supposed to be Kokomo. That's where I live. It's even worse than how it's portrayed in the film, though not necessarily in any way the involves country music.

I've gotten OK sound at some of the places in Indianapolis. We played at Zanies Too last month and the sound wasn't bad. We're playing there again next month, so you should come check it out Brian! The sound at Birdie's is decent too. Their sound guy really liked my amp! Sound at the Emerson pretty much sucks.

But as far as running a power cable for a distro from the kitchen of the bar, the chances of the bosses allowing you to do that around here are slim to none. There are some very strict ordinances about running mains cabling all over the place like that. And if you don't have a licensed & bonded electrician doing it for you, you're pretty much out of luck.
Pushtone, I know this may sound strange, but there are parts of the U.S. where the quality of life and the level of modernization are below Third World status. I mean this literally and without exaggeration. I can show you neighborhoods where you'd swear you were in a bombed-out warzone, and towns where you wonder if they even have electricity or running water.

absolutely - let me know when you guys come back around indy...
also, we are playing up near carmel (north indy) on the 28th this month if you are going to be around, you are welcome to come

bw

[wampcat1]

also, I don't think I've ever played a club where we were allowed to go back in the kitchen... usually the bar owner points to a lone plug that is hanging out of the wall and says "there's your power, make the best of it"

[soulsonic]

also, I don't think I've ever played a club where we were allowed to go back in the kitchen... usually the bar owner points to a lone plug that is hanging out of the wall and says "there's your power, make the best of it"

My point exactly!!
Email me so we can keep in touch about shows!

[Paul Marossy]

The isolation has to be between the guitar and the amp, or between the vocal mic and PA console.

My thought was to put something between the microphone and mixing board/PA system. Like a box that has a male & female XLR jack with transformer isolation. I dunno if it would work in the real world, but it was just a thought...

[Sir H C]

http://www.audiogear.com/cgi-bin/shopper.cgi?key=RPCOISOBLOX&preadd=action