Shocking!

Ryan300000

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Over the weekend, I was playing my tele through my SF Vibro Champ. There is quite a bit of buzz from the guitar, but it stops when I touch the strings. Unfortunately, I made the stupid mistake of touching a microphone while holding the strings and got the worst shock of my life. What can I do to prevent this from happening again (aside from not touching the strings and microphone at the same time)?

Some background: The amplifier has a 3-prong grounded power cord, which was installed before I got it about 12 years ago. I upgraded the guitar pups to 51 nocasters and wired it to the 50s wiring schematic (rear position is blend of both pups, middle is neck with no tone, and front is neck with volume rolled off). Before this happened, I had been wondering if the guitar was properly grounded, but the bridge pup is already grounded to the plate, right? So, as far as I know, I shouldn't have to do anything further than that like running a wire from the bridge to a pot. One note, which may have nothing or everything to do with this: When in the back position (which is primarily what I use) and adjusting the blend knob, there is some crackling noise as I turn the knob. Could that be the cause of this issue? I have been planning to re-solder those wires, but just haven't gotten to it. (If you couldn't already tell, I'm fairly knew to wiring guitars, so pardon my ignorance!)

Any advice will be appreciated!
 

Si G X

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Well it's consistent with a bad ground somewhere, either the amp, wall socket, whatever the mic is plugged into. ... the shock is voltage taking the shortest path to ground, that really shouldn't be the case if your gear is grounded properly.

Maybe start with teasting the socket and work your way back?
 

AAT65

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Sounds like maybe the reference / ground for guitar and mic is different. I think your guitar is doing what it's meant to - the strings / metalwork are grounded.
What is your mic plugged into?
Do you have a meter that you can use to check continuity between all the grounds (guitar, guitar amp, mic input)? Also look for any voltage difference between guitar and mic inputs.
 

Ryan300000

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The mic was plugged into a keyboard amplifier, which has one mic input. I do have a multimeter, but I'm unsure of exactly how to go about checking continuity between all of them.
 

bebopbrain

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have a multimeter
I would start by recreating the scene of the crime, setting the multimeter to AC volts, and measuring between the microphone body and your guitar bridge. It might show 120VC. It might show zero if the shock you got was the equivalent of a capacitor discharging.

If you see real live AC voltage then you want to figure out if you have AC voltage between your guitar bridge and earth ground. Try to get earth ground from something like a water pipe. If there is no voltage, test from the microphone body to earth ground.

If one is bad, swap their sockets and try again. Did the problem move?
 

corliss1

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Test the outlet. One of those little $5-10 outlet checkers is great for this.

If that checks out okay, something is up with the Vibro Champ, as it would be incredibly unlikely for anything modern enough to have an XLR input be the problem.
 

Ryan300000

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Yes, I have an outlet tester and will check it tonight. Is there anyway to safely check the amp to confirm if it's grounded properly?
 

corliss1

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An easy way to check the amp ground would be to set your multimeter to continuity/ohms and check from the ground lug on the power cord to the chassis. You should get a low resistance reading, or some meters beep to confirm continuity.

That won't tell you if the hot and neutral are wired correctly in the amp, but it would let you know the safety ground is at least there and doing something.
 

JamesAM

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the guitar is a passive instrument that uses your amps reference to ground - it doesn't generate any current or voltage, so the grounding of your guitar shouldn't apply here. As other folks who are way smarter than me suggested, check the outlet and then check the amp. Could be that the polarity of that outlet (neutral vs hot wires) is wired wrong, or the ground is no longer there to your house (low probability, but bad!) or the polarity of the amp is wired wrong (more likely, but easy enough to fix).

Definitely check your outlet first - that should tell you how to proceed next, and whether to check your amp...or, to alternatively check if your outlet's polarity is off or if the ground wire from your panel got cut by a weedwacker or something.

occams razor says that the three-pronged power cord that was installed is spliced to the wrong transformer primaries, but probably better to rule out that your house is wired wrong first!
 

Ryan300000

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Okay, I tested the outlet tonight and there is an open ground, so I have my answer. Thanks to all of you for your advice. I’m actually relieved that it’s not an issue with the amp. I have an electrician friend who I’ll ask to take a look at that outlet for me. All the other outlets I tested were fine. Go figure.
 

Ryan300000

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I keep one of those in my gear bag at all times. It only takes one severe shock for you to learn a lesson!

When it happened to me our bass player saw a blue spark jump from my mic to my face. I blacked out for a couple of seconds, luckily it wasn't fatal.
Yep, I learned my lesson and will also keep the tester with me to check outlets before plugging in. Man, your experience sounds much worse than mine, but I swear I felt a strong surge of electricity shoot straight up my arm to my shoulder. I've been shocked before, but nothing like that.
 

notmyusualuserid

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First of all, get a plug in socket tester, there are many to choose. Work from there.


06-tbd05506051-1.jpg

Then watch this vid ;)

 

Dana Rudd

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Glad you found the problem. Sixty years ago I took a shock while holding my guitar and touching another guitar at the same time. Amp had that switch which would change polarity. Switched the position and solved the problem.
Glad you weren't hurt any worse and know what to fix. Play on.
 

Moldy Oldy

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Haven't tried that yet. TBH I'm not looking forward to it!

Before you fix the outlet do bebopbrain’s test so you know what bad looks like. Then do the same test while plugged into a properly grounded outlet. This should give you confidence that you won’t have a repeat. If you don’t know how to do it, I’m sure your friend will.

Also when doing a touch test, don’t put one hand on the guitar strings and the other on the mic. If there is any voltage between them the ”circuit” will go right through your heart.
 




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