multi-effects processor, no ground wire

[pedrorf]

I'm glad I found a forum with such knowledgeable people, and I hope you can help me out on this. I'm completely new to electric guitars, and I don't know much about electronics either, so please take that in account. My guitar is a telecaster, and I'm connecting it to a multi-effects processor, which I use as a practice amplifier, through headphones. Said processor is powered by an external 9v transformer (wall wart) connected to mains. No ground connection: it's one of those double insulated things, without a ground wire).

Now I'm posting this because there's a buzz when I'm not touching the strings. I know this is a common issue, and I've read about it on the guitarnuts site. I am just wondering if, considering the lack of a ground wire on the multi-effects, I may be in any danger of electric shock. The fact that I'm grounding the strings, or whatever, kind of worries me in this circumstances. Would it do any good, safety wise, if I shielded the guitar as per the instrucions on the web site? I know it would probably help with the buzz, but I'm far less concerned with the noise than with the risk of electric shock.

Thanks for your help,
Pedro

[ashcatlt]

Welcome.

I'm sure Sumbody or another around here can explain this a lot better than I can. I'd love to read it myself.

In the meantime, I'll take a stab from my own realm of limited understanding.

Firstly, I'm pretty sure that the strings are grounding you.

Then, I think the safety ground you find on various pieces of equipment is there in case of some catastrophic failure inside which places a dangerous voltage onto the metal chassis of the unit. Drains that off to ground quick, and usually blows a fuse or breaker, hopefully at a time when you're not physically touching it.

I think this is pretty much impossible in the case of the unit you've described. The voltages and currents on your side of the wallwart transformer are so low that, by itself, it can't give you anything much worse than the bite you get from sticking your tongue on a 9V. The transformer itself will explode (possibly causing a fire) long before it passes anything dangerous.

I'm not completely sure that it won't be an issue when interfacing with other equipment, though.

[sumgai]

pedro,

Hi, and welcome to the NutzHouse! ;D

ash is correct, the electrical ground issue does not arise when using double insulated equipment such as your wall wart. In fact, that's the best safety device possible, it's too bad that the National Electrical Code never understood the benefits therein.

Where you normally call it 'grounding the strings', again ash is correct, but this time, we're speaking of electromagnetic radiation, not electricity. They're often confused, and easily so, but they are two separate animals.

In short, you are not in danger, your equipment is not in danger, and unless/until you do the QtB job, your guitar is acting normally. Your question "would it do me any good safety-wise if I were to shield the guitar per the website instructions" is a valid one, and is answered thusly: No, it wouldn't do you any good, given your situation. You don't state it explicitly, but you imply that you are not using a tube amp. Since the QtB article is aimed only at one specific fault caused only by tube amplifiers, you won't get any benefit, safety-wise. Noise-wise, however, the benefits are impressive! ;D

HTH



sumgai

[pedrorf]

Thanks for your replies. Glad to know these things are safe. I might shield the guitar anyway, later on, but for now I'm too busy practicing.

Pedro