OT - FireFly Question - Doug?

[Paul Marossy]

smoguz:

Quoting the electric shock section at www.guitarnuts.com

"Failure of the guitarist's own amplifier places a lethal voltage on the "ground" side of the jack and thus on the strings.  This scenario is usually only encountered on early vintage equipment.  Even then such failures are extremely rare but when they occur they can place hundreds of volts DC on the "ground" side of the jack and the failure may be difficult to detect until the shock knocks you on your backside.  This failure is basically impossible with modern three-prong equipment plugged into a properly grounded three-prong mains outlet.  Never use ground lift adaptors on power cords!  
The shock path is from the amplifer, through the guitar chord to the guitar bridge and strings, to the guitarist's fingers.  From there the shock path either goes through the guitarist to the floor through his feet or through the guitarist to a grounded piece of equipment such as a microphone.  Even the first path through the resistance of shoes and floor covering may sometimes be lethal because the voltage potential is so high.  The second path is easily lethal because the path from the guitarist to earth ground has very little resistance to the flow of current."

I really don't know much about the electrical systems in Europe, I just know that it's higher voltage than we use in the U.S.
In theory you would have to ground the electrical system in your house in order to use a 3-prong power cord.

[smoguzbenjamin]

That's kinda hard, gonna have to tell my guardians to ground the place and I'm sure they won't do that.

However, my SS amp has a grounded plug, and all the sockets in my room are ungrounded, but does that mean that I'm at the risk of being shocked? :shock: This is confusing... :roll: And it's kinda putting me off makin a tube amp simply 'cause I'm scared :lol:
Gonna suck up to the local tube amp man next week. Maybe he'll help me, he obviously lives in europe he must know more about the electrical system here... No offense to you Paul

By the way, what's a 'ground lift adaptor'?

[Paul Marossy]

A ground lift adapter is a little thing you plug your 3-prong cord into, which effectively disables the ground connection to the wall receptacle - there is no connection to ground with this type of adapter. They are actually designed to enable one to plug a 3-prong cord into a 2-prong wall receptacle which doesn't have a ground. There is a little tab on the adapter that is supposed to be fastened to your j-box behind the receptacle faceplate, which will only work if it's made out of metal. Here in the U.S., all of those j-boxes in residences recently built are plastic, so the adapter is useless unless you run a wire from the adapter to some ground point, which can create hazards, too. But, all of the new buildings being built these days have a ground system, it's required by the building codes.
It's a common "trick" that people here use to try to get rid of hum problems. What people should be doing is finding the source of the ground loop causing the hum and dealing with that (if it is indeed a ground loop). Sometimes poor power filtering won't get rid of hum.

Anyhow, no offense taken.  

[smoguzbenjamin]

I could use a 30 foot grounded extension cord and run it from the laundry room to my bedroom, only when I wanna play through my tube amp or something like that. The laundry room (with the desired grounded plugs :twisted:) is right next door to my bedroom

But out of curiosity, if you don't connect the ground to the earth socket, where's all the current gonna go? It's not gonna disspate into nowhere... :roll:

[Paul Marossy]

The equipment that you plug into the wall receptacle will draw only what power it needs to operate. Grounding is a seperate issue. All your equipment has to do is make a complete circuit somewhere in its circuitry for it to operate.

The extension cord is a good idea.

[smoguzbenjamin]

That was the entire problem :roll: I can't see a circuit in the schemmos. Just a collective ground, but nowhere fro that ground to go. Am I missing something here?

[MarkB]

does the 3rd prong of the AC plug go to the chassis along with all of  the star-grounding?
"-)

[Paul Marossy]

smoguz-

Electricity always wants to complete a circuit. In a circuit, ground is a common connection between everything in the circuit that goes to ground.
When you ground your main power supply, you are creating a path for the electricty to flow somewhere besides thru your body to ground in the event of a failure in the main power supply.

[smoguzbenjamin]

That is exactly what I was thinking. So without the grounded plug, the electricity would go through me and not anything else to ground, correct?

If that's true, europe's AC is wierd. Lemme check up on plugs here...

[Paul Marossy]

Correct.

As far as the wiring in Europe, it depends on how old your electrical system is I imagine. I would assume stuff being built today would be grounded, this should be an international standard today as far as I know.
There are older buildings in the U.S. with the same problem.

[smoguzbenjamin]

That is completely wierd because my SS 10W amp doesn't fry me without the grounded plug. There must be one hot and one cold pole or something similar.

This house is 25 years old... :? Maybe that has to do with it. The energy company's website is most uninformative too. :evil: Time for some extensive research

[Paul Marossy]

Well, like the quote said, it's extremely rare to get electrocuted with those vintage amps that weren't made with grounded power cords, but it can happen.

Just pointing that out is all. It's a safety thing.  :wink:

[smoguzbenjamin]

Yeah I know but I'm rather safe than dead if you see what I mean

But the whole problem for me is that the schematics for tube amps are all based around grounded plugs. Without the grounded plug, where's the current gonna go besides through me? I'd need to convert 'em somehow.

[Paul Marossy]

The chassis is acting as your ground. Where the problem comes in is if you have a failure inside the amp of some sort that puts a voltage on the ground side. It's going to want to take some path to ground, and it could be your body, if the power cord isn't grounded and conditions are right. It's rare, but it can happen.

[smoguzbenjamin]

:? :? :? Now I'm confused. The only chance of getting electrocuted, is when your amp fails and shorts, so there's a voltage on ground. OK, fine. But in electronics, there should always be a full circuit, right? Now look at the ax84 P1 schematic: http://ax84.com/media/ax84_m37.pdf

All those ground points connect to eachother, OK. Does the center point of all those points coming together act as ground? If so, no current can flow... :? So my guess was, OK it goes to the ground of the wallsocket. But now there is no grounded wallsocket... Am I missing a valuable piece of information here? Or will the current just flow to the ground point and somehow disappear? Could you explain that please, Paul? Where does the current flow back to?

When you ground your main power supply, you are creating a path for the electricty to flow somewhere besides thru your body to ground in the event of a failure in the main power supply.

in the event of a failure in the main power supply But whatabout when everything's working fine?

[Paul Marossy]

When everything is working fine, there is no problem. Agreed.
If you put a device between the hot and neutral in your wall receptacle, it completes the circuit and current will flow. These are the two prongs on an ungrounded power cord.

[smoguzbenjamin]

Okido. :mrgreen: But what about the DC from the power transformer? That goes to the chassis, right, after coming through tubes/resistors and whatnot.