Please tell me why I got a horrible shock

[Gaz]

The irony here is that I wasn't working on an amp, just recording with one.

While recording electric guitar I went to check and see that I was plugged into the correct jack on the cab - one of them is very loose. I muted my strings with my right hand, and soon as I touched the metal casing on the cable I felt a horrible shock through my chest.

After the initial frustration wore off, I decided to troubleshoot. I turned on the amp and checked for AC and DC from ground to cable - nothing.

I then checked from the guitar strings to jack, and got a reading of -120 VAC, a reading, which I couldn't reproduce when checking again.

I also checked to see if the out let had a bad ground, but that was okay too.

This was my signal chain:

Guitar -> tuner using 9V ungrounded power supply -> amp

All power was coming from a Furman power conditioner.

Any ideas why I was shocked? I've never been shocked while working on an amp because I know how to do that safely enough, but this seems totally random. Thanks for any advice.

-Alex

[Enzo]

If you were to take the speaker cord from an amp, pull it out of the cab jack, and just hold the tip in your fingers, you would find it is not hard to shock yourself if you strum the guitar loudly.

Most amps have the input jack, and thus your guitar, grounded to the chassis. Even if not right at the jack nut, someplace closeby inside. Most amps have the speaker output grounded as well. Again, if not to the chassis at the nut, at least by wire.

SO It concerns me how you would get ANY voltage difference between guitar plug and speaker plug.

What comes to mind for me is a bad speaker cord or bad speaker jack on the amp.

If the ground wire on the speaker cord is open or broken off at the plug, then the plug body at the cab is essentially wired to the hot side. (The output of the amp comes down the hot wire, through the speakers themselves,and on to the barrel of the plug.) If you touched this while grounded to your guitar, and made a loud sound with the amp, the speaker wouldn;t make the sound because the wire was open, but you'd also complete the circuit from that plug body to ground... through your own body.

That is just a thought, might be something totally different.

But I would explore the cords for intermittents, power cord included.

In US power wiring, the ground and neutral are connected together in your service panel. If the plug on your amp is miswired, swapping ground and neutral, most times the amp will work just fine, but it would be using the ground return for its neutral. If the cord was intermittent, you might never know it.

Is your AC plug molded on or an installed replacement plug? If so is the wiring right inside it? Green to ground white to neutral.

[Gaz]

Enzo,

Thanks for the thoughtful response - I'll keep investigating tomorrow and see what I find. I'll make sure to post my findings seeing as I'd really like it if this didn't happen to anybody else. Gettingn shocked is so depressing

-Alex

[Enzo]

Those are just what came to mind right away, I could be way off base.

[martin manning]

...I went to check and see that I was plugged into the correct jack on the cab - one of them is very loose.

Maybe the problem is here?

MPM

[Gaz]

I think I found the culprit... Intending to move the ground for the speaker jack to a different spot on my ground bus, I accidentally soldered to the wrong turret. The NFB was disconnected, so there was no auditory clue I'd done something wrong. There was a haptic clue however. Thanks for the advice.