DC shock protection. is it real?

[UnklMickey]

Hi all,

i know this sounds like heresy,

but, can anyone tell me how you could get a DC shock from your amplifier?

i think i have determined a remote possibility, but it is really remote.


does anyone have any ideas?


unk

[RandomHero]

I do, I do! It's simple.

All that has to happen is that something has to go terribly, improbably, rediculously, bad-karma-doused WRONG.

But heck, it might. *shrugs* Might wanna ring up John A. on that one. He seems adamant enough about protecting yourself against it to know at least a couple cases where it's happened before.

[johan]

Of course, way back in the sixties:



-----
*Keith Richards' electrocution up for grabs*

1965 film showing the Rolling Stone's near death auctioned
The moment Keith Richards almost died is up for grabs.

A Super 8 film showing the Rolling Stones' guitarist getting electrocuted on stage in 1965 is being auctioned through memorabilia site Itsonlyrocknroll.com.

Capturing the moment during the Sacramento gig in colourful detail, the film shows Richards hitting the stage floor after his guitar strings accidentally came into contact with an underground microphone.

Attendants then rush ove to help revive the guitarist while his bandmates Mick Jagger, Bill Wyman and Brian Jones move towards Richards in shock, the New York Post reports.

"I woke up in the hospital an hour later," Richards later recalled. "The doctor said (electrcution victims) come around or they don't."

Medics later said they believed the rubber souls of guitarist's Hush Puppies shoes saved his live from the electric shock which bassist Wyman recalled left Richards' guitar strings "curled up, melted like fuse wire".

The film is expected to fetch around $10,000.
www.nme.com/news/rolling-stones/21795
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With modern amp and setups, it is less likely of course... but still...
-----------------
The Calling's Guitarist Electrocuted In Bangkok
Friday April 05, 2002 @ 04:30 PM
By: ChartAttack.com Staff

The Calling

Check one, check one, two, is this thing on?

Soundchecks are always an important part of any musical performance, but sometimes they grind a show to a halt before the audience has even filed into the venue.

The Calling 's lead guitarist Aaron Kamin was seriously electrocuted during sound check at the Brew Pavilion in Bangkok yesterday. Kamin was immediately taken to the hospital where he was treated for burns on his hands, from which he is now recovering. He's subsequently been released from hospital.

www.chartattack.com/damn/2002/04/0501.cfm

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now you got what you want, do ye want more?

electrically yours,
J

[UnklMickey]

johan said:

...now you got what you want, do ye want more?...

thanks Johan,

but i didn't actually get what i wanted.


those are incidents where the AC mains power was applied to some of the ground circuits.

in those cases, the cap John A. calls for would certainly keep the strings from melting.

but it would only lessen to some degree, the possibility of death.


what i was asking, is about the possiblity of DC shock from a faulty tube amp.

what i want to know:

can anybody explain what kind of failure(s) would have to occur inside a tube amp to put a high voltage DC potential on the strings of your guitar?




RH,


"All that has to happen is that something has to go terribly, improbably, rediculously, bad-karma-doused WRONG."

i consider the possibility that something may fall off of an airplane, and fall on my head.

wearing a crash helmet whenever i walk outside could save my life.

but i don't wear one, just so i can go outside "safely", and don't suggest to anyone that they do.


that's an extreme example, but what i'm trying to determine is, how close to that kind of infinesimally small probability, is a DC shock. or is it really much more likely than that?


i would definitely like to send an e-mail to John A. but i thought i'd filter things out here first.

maybe i'm not seeing the all the possible failure mechansims.

if you could, please PM me with his e-mail address.

i'm sure he doesn't want that out in the public space.



thanks,

unk




still looking for ideas and insight!

[sumgai]

unk,

OK, I follow what you're getting at. (I didn't quote you, your post is right above this one.)

JohnA's difficulty with leaking DC has to do with rectifier circuits, and/or malfunctioning transformers. I am not in awe of the thinking behind this, but I freely admit that I am narrow minded in that my experiences guide me more than anything else. However, I am forced to admit that, in theory, if there's a possibility, then it should be explored, and if the risk is above zero, then the risk to prevention ratio should be examined closely before ending all discussion. (end of disclaimer)

In point of fact, if your favorite filter cap shorted, the fuse should blow, right? What if Joe Blow, the new roadie you hired last week, had found the blown fuse, and had replaced it with a bunch of wadded up aluminum foil? Before the house mains will blow, it's definitely a possibility that the amp's full DC will appear on the ground circuit. Close to zero, but not fully zero.

Strike One. (Or more positively for JohnA, vindication #1.)

What if the output transformer blows it's core shielding, can the DC flow to ground? And why would they (the UL, among others) require a "hi-pot" test, if not for this very eventuality? Indeed, it has happened before, and often in the early days of the All-American 5 radio sets.

Strike Two.

The power transformer, is that suseptible too? Only if the entire rectifier section blew out, but then again, if that happens, then we no longer derive DC, so the narrow answer is no, not here.

Ball One.

Any othe parts that might do this? Not really, unless you count the astronomical odds against, say, a tube failure that put the plate voltage on the cathode, and even then, you're supposing that the cathode is just far enough above ground to not blow the fuse, but that's a wild supposition, and I refuse to entertain it seriously. No other parts come to mind, for the same reason.

JohnA is not attempting to scare anyone, but like I said before, he is being cautious in the right direction. Better to be alive to b1tch at the roadie than to have your widow do the b1tching, right? ;D

Oh, and Keith's situation was a "mere" alternate power leg ground problem, exacerbated by the split 220 volt feed to the equipment (usual in most large venues). It was not due to any condition of the amp itself. In fact, in all the time that I've been in this business, there has been only one recorded death by electrocution on stage. Lots of musicians have bought the farm via some bizarre circumstances, but all of those have been off stage. Google returns lots of dope on this.

Bottom line: Do I isolate my guitar for DC shorts? Nope. I don't let anyone else touch my amp(s), so I know there ain't anything funny going on inside the fuse holder!

HTH


sumgai

[UnklMickey]

"Strike One. ... "


i think i'm gonna have to call a balk here.



with the exception of the case where you would have a output transformer failure , AND were using a two-wire line cord, i don't think you've demonstrated how a lethal voltage could be present at the shield of the guitar cable relative to ground. (you need both failures for this to occur.)

in that case, i do see the possibility.

but who would use such an amp? i think the cure here, is a 3-wire line cord and a ground testing lamp in your kit.

that also helps prevent the AC shocks that the cap won't really protect you from.




in the case of a 3-wire system, how would it be possible to get more than a volt or two present on the shield of the guitar cable without a statisically improbable, multiple failure occuring?

lets say you had 50A flowing from your power supply (this is rediculous, i know) right into the chassis at the point where the input jack is connected. and there is say, 1 ohm of resistance from there, to where the other end of the chassis, power supply, and ground wire of your line cord is connected. that would mean the voltage at the shield of the guitar cable would be 50V DC. if you tried real hard to kill someone with that, by connecting it directly to his heart, you just might succeed.

but, i don't know of any tube amps that are using arc welding power supplies.



i'm still looking for a mechanism for a single failure to make those kind of DC voltages to be present.

but in terms of a multiple failure, you have presented one plausible possibility.



"Lots of musicians have bought the farm via some bizarre circumstances, but all of those have been off stage. Google returns lots of dope on this."


musicians...bought the farm...dope...

yeah, all too common story.

[sumgai]

unk,

...
musicians...bought the farm...dope...

yeah, all too common story.

Leave it to you to spot the hidden meaning within the common sentence! ;D

To be sure, I had taken an unspoken shortcut, that of the two-wire power cord instead of 3-wire. Nice catch on your part.

...
but who would use such an amp?

You have to ask??? There's no law that requires common sense before a musician can take up a piece of electrical gear, at least, not one that I know about. The quote just above, and the back story I gave earlier about bizarre circumstances can all be traced to a moment of stupidity and/or gross negligence.

lets say you had 50A flowing from your power supply (this is rediculous, i know) right into the chassis at the point where the input jack is connected. and there is say, 1 ohm of resistance from there, to where the other end of the chassis, power supply, and ground wire of your line cord is connected. that would mean the voltage at the shield of the guitar cable would be 50V DC. if you tried real hard to kill someone with that, by connecting it directly to his heart, you just might succeed.

Welllll, let me tackle that in reverse. One need only experience about 1/10th of an amp, across the chest cavity, to suffer permanent heart damage, if not outright failure. 1/2 amp guarantees failure, most quick and nasty. 50 amps, if it could be arranged such as by an arc welder, would not leave anything between the contact points to determine by autopsy if the heart had failed or not - the body between the two points is a crispy critter. Gruesome.

The other point I wanted to address was about flowing 50 amps from one end of a chassis to the other (line cord ground to input jact ground). unk, never mind what the player might experience outside of that chassis, don't you think that he would have to be smoking some serious weed to be able to ignore the heat, and likely the smoke, coming up out of that thing?


sumgai