Watch this video, it will shock you - no pun intended. (Audio Noise And Grounding, right hand side)
http://www.taylorguitars.com/videos/?id=52&tab=ss&pg=1
A very good illustration of something more people should be aware of.
cool vid ...yep ive had shocks off mics at various gigs.......nasty....
Quote from: deadastronaut on August 13, 2010, 05:14:42 PM
cool vid ...yep ive had shocks off mics at various gigs.......nasty....
Happened to me once, too - on an outdoor gig running on a generator!
Kind of scary when you can have a 60V AC differential between the ground of the PA and the string ground on your guitar. :icon_eek:
wouldn't the fuse to the amp/microphone's PA/shop fuse box just blow if the current started flowing between the mic and his teeth?
I was about to buy a second hand amp from a friend once, until he told me that it kept blowing fuses and that he put a piece of wire where the fuse goes.
Very good information, and really easy to understand. I was given one of those voltage pens for Christmas last year.. cool to know that they aren't just novel pieces of junk
Quote from: guitarbobby on August 13, 2010, 05:44:31 PM
I was about to buy a second hand amp from a friend once, until he told me that it kept blowing fuses and that he put a piece of wire where the fuse goes.
:icon_lol:
wouldn't the fuse to the amp/microphone's PA/shop fuse box just blow if the current started flowing between the mic and his teeth?
Which one ? Just not me.
Just a super-nasty shock is the good news, the other good news is everything is on a ground [desert show caveats].
Very demonstrative of the LVDetector, nice little gadget !
I was about to buy a second hand amp from a friend once, until he told me that it kept blowing fuses and that he put a piece of wire where the fuse goes.
There's a reason for that, and it's reason enough to suggest it as price consideration.
The only thing worried me is ''the world is a safe place'' [after he said 10 times 'very/dangerous situation']. It is safe if you make your grounds, certainly.
Buy gear that has 3prong AC cable, at both ends.
Read
http://geofex.com/Article_Folders/Power-supplies/powersup.htm
Some linear supplies only need the IEC connector installed [with super secure ground/Lug/chassis connection, wedged tightly in place].
Others amps have no PT, so a quick ground fix isn't possible...not designed for connecting to humans or modern equipment.
Quote from: guitarbobby on August 13, 2010, 05:44:31 PM
wouldn't the fuse to the amp/microphone's PA/shop fuse box just blow if the current started flowing between the mic and his teeth?
Very definitively not.
Fuses are rated to NOT blow until the current through them is bigger than their rating. A 1A fuse will NOT blow until the current through it is more than 1A for some period of time. Fuses only know the current that's flowing through them, and how much it is. They can't tell that the current's going where it isn't supposed to.
Nor will a 3A or bigger fuse, common for guitar amps and PAs, protect you. it takes about 20ma of line frequency current through your chest to send your heart into an irrecoverable fibrillation, and you die unless someone has a heart-shocker setup handy. The fuse would not even notice this small an amount of additional current.
A common cause of hum is feedback voltage on the ground.
Quote from: R.G. on August 13, 2010, 06:38:34 PM
it takes about 20ma of line frequency current through your chest to send your heart into an irrecoverable fibrillation, and you die unless someone has a heart-shocker setup handy.
:icon_eek: :icon_eek: :icon_eek:
so what are the fuses for? I've seen someone touch a live wire (by accident) and all that happened was he said he felt a big electirc shock, and the fuse box for the house went, and the switch just had to be reset (i.e. all the electrics to the house were cut off, lights, fridge, etc) im also ashamed to say that years ago (junior school ago) I innocently put a knife into a toaster to get a piece of bread out! again the house elcetrics went out and I didnt feel an electric shock at all (but I was scolded no end)
did the guy in the video disconnect the earth pin? because i thought that (UK) plugs worked in such a way that the earth pin goes in first, and releases the flaps for the live and neutral pins to go in. if there is no earth pin, tthe flaps stay shut and there is no circuit. but what do i know
also, pretty much every gig I have played, no matter how small, if it is public, things like plug sockets have to be PAT safety tested. once I even had to buy about 8 of the 9v batteries just to run my pedal board because the power adapter hadnt been tested, and the techies refused to let me use it!
i have a peavey special 150 amp with a ground switch on the front panel, + on one side, O in middle position,and - on the other side.
my fender head also has an a,off,b ground switch...
does that mean that in the middle position, of each, that it is lifting ground?
i usually keep em both alone peavey on - and fender on A ...
or is this somehow a safe way to ground lift inside the amp, as opposed to running it without the 3rd prong? or something different?
??? should i pay close attention to these switch settings to avoid a dangerous shock?!? or are they somehow isolated safely ?
i always use a proper plug, and generally a surge protector as well...
Without the 3rd prong, the chassis isn't grounded.
With a solidly wired safety ground, greater happiness and greatly reduced chance of tragedy can be guaranteed.
Quote from: R.G. on August 13, 2010, 06:38:34 PM
Fuses are rated to NOT blow until the current through them is bigger than their rating. A 1A fuse will NOT blow until the current through it is more than 1A for some period of time. Fuses only know the current that's flowing through them, and how much it is. They can't tell that the current's going where it isn't supposed to.
Nor will a 3A or bigger fuse, common for guitar amps and PAs, protect you. it takes about 20ma of line frequency current through your chest to send your heart into an irrecoverable fibrillation, and you die unless someone has a heart-shocker setup handy. The fuse would not even notice this small an amount of additional current.
Does that apply for a fast acting type, too? I know that amps use the slow blow types so the inrush current doesn't blow them. It's scary how small an amount of current can actually kill you, in the right set of circumstances - 20mA is not much current at all.
Quote from: petemoore on August 13, 2010, 09:21:58 PM
Without the 3rd prong, the chassis isn't grounded.
With a solidly wired safety ground, greater happiness and greatly reduced chance of tragedy can be guaranteed.
Yeah, that and the ground is now "floating" on that piece of equipment. That creates a voltage potential between grounds like you see in that video. It's interesting that what people think is helping with noise by defeating the ground is actually making matters far worse as far as noise is concerned.
Quote from: guitarbobby on August 13, 2010, 08:50:45 PM
so what are the fuses for? I've seen someone touch a live wire (by accident) and all that happened was he said he felt a big electirc shock, and the fuse box for the house went, and the switch just had to be reset (i.e. all the electrics to the house were cut off, lights, fridge, etc)
The fuse is often there for the equipment's sake, to keep it from getting damaged. In your friend's case, the circuit breaker did its job and protected him from potentially being electrocuted to death. He became the path to ground and made the breaker trip. It sounds like that circuit breaker he tripped might have been tied to the GFCI circuit in the electrical panel (if there is one, it's been required for something like the last 20 years).
That particular video doesn't show up for me. It shows the title and all but no video. Anyone else having this problem? I'm on a Mac which could be the issue.
Quote from: dmc777 on August 13, 2010, 10:13:04 PM
That particular video doesn't show up for me. It shows the title and all but no video. Anyone else having this problem? I'm on a Mac which could be the issue.
Might be the problem. Here is a direct link to the YouTube video: http://www.youtube.com/watch?v=6ZGokkrsO_Y
Even if your amp is properly grounded, you may run into trouble with differing grounds among outlets at a gig or even your friendly practice space. I discovered this the hard way, when, while practicing in a garage, the other guitarist's (uncut :P) string brushed my arm, sending me a nice shock. We were both using 3-prong, properly grounded amps. However, we were not plugged into the same outlet, and the difference in ground potential for each outlet was enough to feel! So, if you have a meter with you, simply testing the voltage between your strings and the other player's strings should give a good indication of proper outlet grounding.
Quote from: mohn on August 13, 2010, 11:47:45 PM
Even if your amp is properly grounded, you may run into trouble with differing grounds among outlets at a gig or even your friendly practice space. I discovered this the hard way, when, while practicing in a garage, the other guitarist's (uncut :P) string brushed my arm, sending me a nice shock. We were both using 3-prong, properly grounded amps. However, we were not plugged into the same outlet, and the difference in ground potential for each outlet was enough to feel! So, if you have a meter with you, simply testing the voltage between your strings and the other player's strings should give a good indication of proper outlet grounding.
Yeah, you can't be too safe when it comes to this sort of thing. What I found really interesting in that video was when he disconnected the amp from ground and everything had AC coupling going on - the mic cable, the guitar cable, the guitar. I really didn't know that there was all that going on when you have a piece of equipment not grounded (I have never defeated the grounds on any piece of equipment). I mean I know that there is some AC coupling going on all the time because we are surrounded by AC in our world, but that little low voltage detector really made things very obvious. Kind of a fascinating phenomenon.
I needed to see it, and my friends too, thanks for posting it.
http://www.youtube.com/watch?v=4YM1iwC6vhg&feature=related
He talks about ground loops here. First he gets rid of the loop noise by disconnecting one of the amps, and hurray the noise is gone. The he lifts the ground of one of the amps, and for some reason the noise is back, which he describes like the noise is the way ... er we expected. Right after that he advises that we should use well grounded amps. A bit confusing video.
Is there some kind of precendent for disconnecting grounds on the USA? I just don't know why anyone would even need telling once!
Quote from: dmc777 on August 13, 2010, 10:13:04 PM
That particular video doesn't show up for me. It shows the title and all but no video. Anyone else having this problem? I'm on a Mac which could be the issue.
Did you go to the bottom of the page?! ;D
Quote from: yeeshkul on August 14, 2010, 06:20:32 AM
http://www.youtube.com/watch?v=4YM1iwC6vhg&feature=related
He talks about ground loops here. First he gets rid of the loop noise by disconnecting one of the amps, and hurray the noise is gone. The he lifts the ground of one of the amps, and for some reason the noise is back, which he describes like the noise is the way ... er we expected. Right after that he advises that we should use well grounded amps. A bit confusing video.
Yeah, I saw that one and initially thought the same thing, too. But the grounds of the amps are still connected together via that A/B box, so I think it's OK to do that. He just broke the ground loop by removing the second ground connection happening at the power cord. Personally, I prefer to break the ground connection at the inputs, but both methods usually work.
Is there some kind of precendent for disconnecting grounds on the USA?
This is not aimed at...anyone here, here how it's been egosplained to me:
"Yah...duhh...whaddya think that grey adapter is for then ? They're made for plugging stuff in, just like this//what they're designed for !
They wouldn't sell 'em if they weren't safe!
It's an adapter...I use 'em all the time and never had a problem."
Imagine these words in a contextual scenario that dictates electric jam, or no jam..."cause all I brought was an electric guitar"...while necessitatively criticizing and being framed as attacking ''dudes knowldedge of electricity'', the vote often goes to the guy who says I KNOW WHAT I"M DOING the most forcefully, [or using the Edwin R. Murrow tone first]...when this happens I know for certain I don't want to be there, for this, and other reasons.
'What is the power supply like?" is an elementary band related question, how well it is answered [over the phone] has everything to do with my level of interest.
See 'Desert Show' for directly related: typical and special power supply ''conversations''.
I have never seen such a device for sale here! And our earth pins are like, 4mm thick, no way you could take one off without a hacksaw, and even if you could, the plug sockets won't allow the live pins to enter without the ground being in there first (so that double insulated things like phone chargers have a dummy plastic pin to fool it!)
I guess that's what happens when the government know they're going to be footing the bill for people electrocuting themselves! ;) They must take you guys for smarter than us :)
Quote from: Hides-His-Eyes on August 14, 2010, 12:13:14 PM
I have never seen such a device for sale here! And our earth pins are like, 4mm thick, no way you could take one off without a hacksaw, and even if you could, the plug sockets won't allow the live pins to enter without the ground being in there first (so that double insulated things like phone chargers have a dummy plastic pin to fool it!)
It's pretty easy to do it here. You could probably do it with a pair of pliers by bending it back and forth a few times. I don't know where people even get the idea that removing the ground on a three prong power cord helps with noise. I think it's in the category of "old wive's tales". How they do things in your part of the world makes sense. Stops people from doing the stupid things people do here.
I bought a used Crate bass amp once that had that had the ground cut off on the power cord in a vain attempt to make the amp quieter and I put a new grounded cord on it but the amp was still just as noisy. I think it was just a poorly designed amp.
I have a couple of powered mackie studio monitors and I get a horrible bassy hum when they are grounded. I didn't hack the pins off but when I use one of those ground lifting adapters the are super quiet. What's the deal there? Is that dangerous since I not touching them or using a mic?
pliers or end cutters'll take the prong off, pliers rip it out better.
Some equipent had a ground...a wire at the plug end you were supposed to screw to a ground.
Other ground defeat adapters had similar lug-tab, I guess to screw the socket-plate screw through.
Some ground defeat plugs don't have this.
Some ground defeat plugs were an adapter that had the ground pin pulled out.
There are 100's of variations, and ''correctly grounded'' either is...or any one of these apply.
Not sure what's up with the monitors and safe is whatever too, probably ther'es something else up with the ground or signal there, do they hum when no signal wire is connected ?
I'm not sure and I'm in the middle of re-modeling my room so nothing is hooked up right now. I'll have to test that out though. My cousin had the same problem with his too, he was the one who told be to ditch the ground.
I'm thinking about what/how to do it.
Put all the grounds in, and test them ?
Worth a try, it seems is has to work.
It's a debug, similar to other debugs, a good start by testing the metal ground clamp at the metal water pipe...then...everything else in that chain.
I bought one of those Greenlee low voltage detectors shown in the video off of ebay the other day. I think it will be a very handy tool for isolating grounding problems and sources of audio noise caused by AC coupling.