Introduction and some questions

[jayquackenbush]

Hi Everyone, my name is Jason and I'm a newbie to the forum. I wanted to ask some of the more knowledgable folks a couple of questions. I'm an electronics hobbyist and I know probably just enough not to be a danger to myself by fooling around with things I know nothing about, but there are still a number of big grey areas i was hoping people could clear up:

1.) On the issue of Safety: I have a lot of friends that do the underground punk rock basement tour circuit and i do some occasional sound reinforcement work, so the electrocution risk is something that I think about a lot. I've personally bought most of my friends outlet testers and I won't plug anything into a PA if it doesn't have an inline GFCI. I'm wondering though, with those precautions are the caps still necessary to protect against a short in an amp? As the local guy who's handy with a soldering iron, if it's still a good idea, then i'll probably be making those mods to my friends' guitars as christmas presents or something this year. But if GFCIs take care of the problem, then I'd rather organize a group to buy a bunch of those in bulk instead. Or are both a good idea, one protecting from crappy inhouse AC and one protecting from a DC voltage from a short circuited amp?

Also, usually there's a warning about isolating the strings that metal knobs and the jack plate will still be hot. I have a frankenstrat with a pickup wiring scheme similar to the S-Tastic mod on the guitar nuts site that uses metal knobs that I like a lot. I was wondering if anyone had thought much about insulation for these parts. Some thoughts I'd had were useing a liquid latex or quick drying epoxy to insulate metal knobs or jackplates? I've tried a couple of ways to wrap electrical tape around the shafts with very little luck.

Also, why is it a capacitor that's used to block dangerous voltages from the ground? my understanding is that capacitors only block DC. Would it be possibl/better to wire in an inductor in series with the capacitor to help deal with AC shock? or would the inductor have to be too large to block ac at 50/60 Hz? I think I'd be willing to do a little extra routing if it meant playing safe.

Also, why use these sorts of reactance to block the deadly voltage? Why can't you just wire a very small fuse between the signal return on the output jack and everything else to act as a circuit breaker? Do fuses not blow fast enough to keep you safe? Also, this raises another question, why wire in the isolating cap between the signal ground and the chassis ground the way it is in the Quieting the beast Mod? Why can't you wire it immediately after the signal return at the jack and thereby isolating the whole of the shielding, pots, pickguard screws, metal knobs and all?

Thanks in advance, and I look forward to talking more to all of you as i hang around here...

-J

[warmstrat]

I think you might be worrying a bit too much, my friend...

As i understand, the risk of being shocked by your guitar is only realistic if you have a malfunctioning (read: old) all-tube amp. Anyone with said type of amp should have it looked at by professionals regularly if they value their lives, i am told... but beside that, as i understand, the risks of being zapped by your axe are pretty much negligible.

Feel free to disagree, i'm no expert, this is just what i've come across so far.

[jayquackenbush]

well, that is one scenario, sure. the problem is that one of the things that can put a voltage on the ground is if the vacuum tubes aren't seated properly and the outlet it's plugged into isn't grounded properly. this combination of events can happen quite naturally with bands that are touring doing houseshows and small clubs, and while i'm not worried so much about myself because i know that everything is wired okay and i take good care of my amplifiers, i do worry about my friends who tour a lot. and it's not as uncommon as you might think. i've gotten shocked by strings and microphones more than a few times in my life, and i've always been very thankful that I didn't get more than a little jolt.

so sure getting shocked by your instrument is rare, but then, it can happen and in the worst cases it can bet lethal, so there's a reason to take precautions against it. my questions are more directed at the sorts of precautions people take. the guitarnuts site, for example, recommended a high voltage capacitor isolating the strings from the ground shielding. capacitors will block DC current, which is the sort of thing you get from malfunctioning amps, but they don't do a lot against AC voltage which is what you get from badly wired mains. an inductor of the right size, by contrast, will block AC, but DC shoots through it like it was just a regular old strip of wire. so, while I'm no electrician myself, i was hoping someone who is closer to that than I am might be able to explain why no one uses inductors to isolate the strings.

[ashcatlt]

I won't claim to be smarter than you in these matters, but I would like to mention that the QTB mod, followed as posted, does isolate all of the metal parts of the guitar except for the jack and any metal attached to it. From discussions we had a while back I learned that putting a cap at the jack (as you suggested toward the end of the first post) will affect the tone of the output. Also that fuses don't blow fast enough to save you from the one (extremely rare and unlikely) thing that this mod is meant to protect against.

I think the smartest guys around here actually just follow the advice given in the electrical shock article and that you'd do best by your friends to buy each of them an outlet tester and print a copy of said article. Maybe laminate a quick-reference card they can keep in their wallets or guitar cases.