Possibly OT, but here goes-
Many of us, including myself, have had the not-so-pleasant experience of getting zapped in the lips by a mic while playing guitar. Beyond the nuisance, it seems that this is not really much of a hazard (confirm/deny?). However, I've read some threads that lead me to believe that in some cases, a guitarist could be at risk. A club you've never plugged in at before could have bad wiring that presents a potential risk. These are a good thing to plug into any outlet you're about to use:
(http://static.howstuffworks.com/gif/how-to-check-electrical-receptacle-polarity-2.jpg)
Quick'n'Easy indication of grounding & proper polarity. Plus they're real cheap...
Beyond that, I wonder if there might be circuitry that could be introduced to an outlet/power strip/effects chain/guitar/etc. that could prevent potential electrocution... I'm not exactly sure what the causes of this potential risk could be, but if they exist, it would seem pretty frickin' smart to go ahead and spend $30 on insuring your own heart!
Any ideas?
zpyder
I go through a bunch of stuff like this in a couple of upcoming articles in my Musician's Hotline "Tech Views" column.
You can get those for as little as $5 if you shop carefully. IMHO, it's silly to do without them. There ought to be one in every musician's gig bag.
GFI power strips exist, and are a good idea.
From there on up, it gets heavy. Really, really good power protection can be had by carting along a 1kva - 2kva isolation transformer, which are quite expensive, but I got a 3kva one on ebay for $50. Weighs 60 pounds, though. 8-)
If your mind works like this, you'll want to see my next couple of Tech Views articles.
I'm curious as to what causes that shock-in-the-lips and how to prevent it altogether...we generally get it in at least one mic. It's not fun...I don't sing really close in to the mic, but if my lips so much as brush it, it really HURTS.
Well, when I mentioned that Polarity Checker in my other post, it was to check if the Ground, Neutral and Live wires were connected correctly.
But if you have a Ground floating somewhere, like in an equipment with an input transformer completely isolated from the Ground, you can easily get 30-50V (that's what I already mesured before in some occasions) between its chassis ground and the chassis of another equipment. Enough to shock your lips.
A better explanation is in the Ground Lift section of this article...
http://www.whirlwindusa.com/ftp/tech/tech06split.pdf#search=%22danger%20of%20ground%20lift%22
From that article:
<If console A "sees" a lower resistance to ground through its c onnection through the splitter to
console B, then part of its AC ground return current will take that path of least resistance.
AC current flows in the shields of the cable, through the splitter, and over to console B. This
is called a ground loop . Now, instead of the shields providing a defense against unwanted
interference, they are carrying 60Hz AC and radiating it directly into the signal conductors>
Btw, remember the Ground Lift Switch in the old Fender amps? Combine that with an old 110V plug that can be plug either way and you're at risk.
Gilles
When I got my current v4b head(and this is one reason I don't use it to play out any more), some idiot had broken off the ground lug. Sadly, the idiot was actually a fully professional(Hell, mtv and everything) bass player. I figured it didn't matter much- some old tube amps never had one, and he must have known what he was doing.
So, my band played a little dump bar, I step up to the mic to sing(no soundcheck dammit!), and WHAM!, the lights actually dimmed I think!(hard to tell, I was seeing spots and everything)
The next day it got a new plug.
Yes, I carry that exact little gizmo with me, and KNEW the board was not grounded because I tested with that, but we decided to go with the juice that was over there because we were pushed for time. DOH! I KNEW better!
The GFI outlet strips seem pricey to me, unless you go through ebay. One trick is to find a GFInterupter plug on a hair dryer at the thrift store too. Chop off the hair dryer, and splice the cord end onto the amp. The wide "blade" on the plug goes to neutral, and the other to "hot"
:icon_idea:
http://www.cablewholesale.com/specs/51w1-10013m.htm (http://www.cablewholesale.com/specs/51w1-10013m.htm)
$18
I'm worth 18 bucks to me... Hell, my bass player's worth 18 bucks to me... maybe I'll buuy him one, too..
zpyder
GFI (Ground Fault Interrupt) = RCCB (Residual Current Circuit Breaker) in UK - much more important in the UK for bands. We don't trust anyone and always use our own RCCBs. Regulations in public premises are a lot tougher than they used to be though so things are generally safe in my experience.
QuoteI'm curious as to what causes that shock-in-the-lips and how to prevent it altogether...we generally get it in at least one mic. It's not fun...I don't sing really close in to the mic, but if my lips so much as brush it, it really HURTS.
What causes it is that the "ground" on the mike is at a different voltage than the "ground" on your guitar. You hold the guitar with sweaty hands and touch the mike with damp lips, and the electricity considers your body to be a resistor. When the state executes someone in an electric chair, they swab the places where the electrodes touch the prisoner with... salty water... to make the electricity conduct through them better.
Preventing it is easy in theory. The practical matters are a little bit harder.
The third wire safety ground contact on the power plug of all your equipment does this if :
(a) it is there
(b) it's connected to signal ground inside the equipment
(c) the wall plug is correctly wired.
Let's take (c) first. The little tester plug that motivated this thread tells you that. Plug it into **every single outlet** that your equipment is plugged into. Verify that the thing says that the outlet is properly wired and that safety ground is in fact connected. If it is not, you come up against one of those practical problems. The
building is wrong. Do you play and risk your life, or say no?
Now let's look at (a). Just look at the wall ends of the plugs. Does each and every piece of equipment have a ground plug? Not cut off, not stuck in an un-grounding adapter? If not, you're risking your life using the equipment. You have a vintage, two wire amp? There are only a few choices. You can upgrade it to a three wire cord. You can keep using it and risking your life. You can sell the amp or otherwise quit using it.
If there is a third prong there (b), it's kind of silly not to have it be effective, isn't it? So get out your ohmmeter. Unplug the amp and touch one probe to the safety ground and the other probe to the signal ground on the end of a guitar cord plugged into the input jack. Does the ohmmeter show a short? If not, you're at risk. Do this for mixing boards, PAs, all the electrical plugs.
What kills you is if you are touching a "ground" that is not connected to safety ground and that "ground" has some AC current leaking to it. If you then touch something that is safety grounded, you get that amount of AC leakage through your body. A little bit HURTS, a lot kills you. Guitarists have DIED from this. It's your job to do the detective work to find out what is grounded and what is not. The life you save could be YOURS.
If you do this well, you may get hum. It happens when the AC wiring in the building is not all that great and the "ground" at one outlet is not the same voltage as the "ground" at another point. Consider this to be the building telling you that the conditions are right to get shocked.
Ahhhh, a Great idea to carry.
The other thing I've done is I rewired my '67 Twin with a Grounded 3 prong plug to make things a bit "safer" but still, this little gizmo
would be a good thing to have.
Just wanted to mention that the surge strip I mentioned earlier also includes an "EMI / RFI Noise Filter" - cool
Aaaannnndddd... a 6ft cord... sweet
I do believe I'm gonna buy two of these (one for the bassist) and an outlet tester quite soon (like, before the next gig)
cheers,
zpyder
Bear in mind also that the faults are not always in the building. They may be in your (or someone elses) equipment. The device shown will not detect faults with equipment unless it is already plugged in somewhere else and generating a fault. That is why it is always better to have a permanent in-circuit earth leakage detector/breaker.
Sounds like you mean a tripp light Isobar. I have a couple of those. They also come with 3 leds that serve the same functions as the little tester gizmo. As far as the filtering, they have it, but I've never heard the difference. I got the impression that it would help filter the wierd digital noise when you have a computer next to an amp, but I just don't do that.
I also don't use them live. The circuit breaker is too sensitive- it trips when you run the power amps thru it, and right in the most inconvenient moments(when you really get going good). There dosen't have to be anything wrong, you just drew more current than they wanted you to. For a few more bucks(Isobars are expensive) you can get a real line conditioner, and eventually I intend to.
Other than the comments that suggest that the neutral wire is a "ground" (it isn't), this is fairly informative regarding shocks and why they happen:
http://www.physicsforums.com/archive/index.php/t-76381.html
:icon_biggrin:
very good article on the very subject:
http://www.guitarnuts.com/technical/electrical/safety/index.php
Quote from: davebungo on October 03, 2006, 08:14:08 PM
That is why it is always better to have a permanent in-circuit earth leakage detector/breaker.
...And this would consist of ... ?
zpyder
GFI breaker. The AC power line breaker itself detects leakage and shuts down. US electrical code now requires these for all locations where there are electrical convenience outlets and water in the same room, like bathrooms and kitchens. The GFI breaker protects all the outlets connected to that breaker. They're about US$15 each when last I bought one.
I do not know about else where but in Canada it is now required by code to use arc fault protection for bedrooms circuits. It will probably be expanded later on to all other circuits.
Andrew
To find the culprit at a show, I will carry a small voltmeter (I do sound), and can measure the AC on the mic and then the gear. I have almost always found the fault to be the gear not the PA system. On a lot of old amps, they have that switch for ground/hum and flicking that the wrong way can be really nasty with the 120 volts going to the chassis through a cap (often the cap is dead too). This can be quite a zap, some have died this way.
Solutions, get the amp properly wired and use the small plug above to verify the outlets (at clubs often they are wired wrong). Sometimes an isolation transformer for the microphone will work too, but this often then means that you touch another mic and get zapped to hell.
Sir HC, what, specifically, do you test with the volt-meter? I.e., where do you touch the leads? Hot and ground?
I think he means carry the mic over to the amps, 1 probe on the mic, the other on the amp chassis. Not a bad idea!