My Gear Electrocutes Me.

[hduncan]

I have a duet plugged into my macbook and it feets two monitors. all of those devices connect to a single surge protector into a wall.

I noticed while changing plugs today that when I touch the tip of the TS cable to my monitor, and the tip of a guitar cable going into one of the inputs of the Duet, it shocks me. stiketutt

Does anyone know why this is happening? I also have trouble with noise sometimes when I plug an external keyboard into my computer via USB, (this problem is fixed when I lift the ground of the keyboard).

Thanks!

[peeder]

Not sure what's going on, but I follow the one-hand-in-the-pocket rule: the most important thing is that you don't have your heart in the path of least resistance to ground. So if you get shocked, you only get shocked on one hand, and not making a circuit that passes through your heart from one hand to the other.

Also NEVER lift safety ground. The jerks who do that are suicidal, and seriously, I can't believe people post online that you should do it. One would hope only they would die, but visitors to their studios, people burned up in fires, etc. could all suffer for their unbearable idiocy.

I should add that while line level is a generally safe current (although it could serve as a conduit for higher current if shorted...and beware of phantom power as well), speaker level e.g. with guitar amps etc. is NOT a safe level to handle, and many speaker connectors are ordinary phone plugs with metal casings that are HOT and could kill you. Speakon connectors with insulated casings should have been made standard decades ago.

[corworld]

Uh yeah, you are causing the speaker level voltage to conduct through your body to the guitar cable. It is not going to hurt you as it is probably only 12 volts or so but I wouldn't change speaker cables with everything on. Stick your tongue on the terminals of a 12 volt battery. Does it feel the same? Why aren't you using TRS cables with your monitors?

[Geoff_T]

Originally Posted by DarkEcho

I have a duet plugged into my macbook and it feets two monitors. all of those devices connect to a single surge protector into a wall.

I noticed while changing plugs today that when I touch the tip of the TS cable to my monitor, and the tip of a guitar cable going into one of the inputs of the Duet, it shocks me. stiketutt

Does anyone know why this is happening? I also have trouble with noise sometimes when I plug an external keyboard into my computer via USB, (this problem is fixed when I lift the ground of the keyboard).

Thanks!

Hi

I should pay attention to the second post and ignore the third... with respect... because the last thing you want to to with your tongue is to connect it to any electrical current... especially one where you have no idea of the voltage concerned!

Elaborating on the second post, from my early background in high voltage switching equipment, it's the volts that jolt and the mils that KILL.

To elaborate, a voltage that has a high resistance path to completion, will make you jolt back but (because you had one hand safely in your pocket) the high resistance means a very low current and you won't be seriously harmed.

But touch a live terminal with one hand while touching a grounded piece of gear with the other hand will direct a current across your chest and it only needs to be around 50milliamps to kill you. The mils that kill.

So this is no laughing matter.

You need to establish if the power socket you are using has a ground connection. There are testers you can buy from hardware stores that perform this task. If in doubt, call an electrician.

I suspect that the wiring in your room needs some careful evaluation by someone that understands the rules. I don't recommend continuing the status quo.

tutt

[theblue1]

Stick your tongue across a 12 volt car battery* (somehow) and you're going to be one very sorry junior scientist.

The voltage may be low but the amps are, well, you know, enough to turn over a V-8 engine. You don't want that kind of power jumping through the very soft and fragile tissue of your tongue.

I don't want to try to guess how much of your tongue would be left (if I had to, not much) but I've seen jumper cables explode away from each other pretty good when someone was careless enough to short them.

BTW... because one's tongue is generally wet, it tends to conduct pretty well.

__________

* A 9 volt transistor battery, OTOH, will give you a nasty little shock across your tongue but probably won't do much besides burn a few nerves and cells and perhaps tastebuds. I'm not sure what the taste is when you do that -- but I'm suspecting it's not happy healthy tongue cells doing their thing. Whether it does any lasting damage to nerves or taste buds, I'd have no idea.

[Geoff_T]

Originally Posted by theblue1

Stick your tongue across a 12 volt car battery* (somehow) and you're going to be one very sorry junior scientist.

The voltage may be low but the amps are, well, you know, enough to turn over a V-8 engine. You don't want that kind of power jumping through the very soft and fragile tissue of your tongue.

I don't want to try to guess how much of your tongue would be left (if I had to, not much) but I've seen jumper cables explode away from each other pretty good when someone was careless enough to short them.

BTW... because one's tongue is generally wet, it tends to conduct pretty well.

__________

* A 9 volt transistor battery, OTOH, will give you a nasty little shock across your tongue but probably won't do much besides burn a few nerves and cells and perhaps tastebuds. I'm not sure what the taste is when you do that -- but I'm suspecting it's not happy healthy tongue cells doing their thing. Whether it does any lasting damage to nerves or taste buds, I'd have no idea.

Hi

It's just a damn silly procedure to bring up when a guy is feeling electric shocks through his hand!

[theblue1]

Originally Posted by Geoff_T

Hi

It's just a damn silly procedure to bring up when a guy is feeling electric shocks through his hand!

Yeah, I thought your post was pretty sobering.

I've cheated death a few times, I think. When I was a kid I was way too fearless. Though I'd lecture others. ('Cause, you now, they weren't as smart as me.) But I'd do really dumb stuff.

[Reptil]

Good advice here! I forget sometimes the one hand in pocket, but everything has solid earth here.

I emailed this some time ago to a good friend and colleage.
He's also head electrician in a large hotel chain.
(380 V +21 A and stuff like that)
AND (!) he's still alive and in good shape.
When seeing it, he said "yeh that's me before, how did you know." LOL

[Geoff_T]

Originally Posted by theblue1

Yeah, I thought your post was pretty sobering.

I've cheated death a few times, I think. When I was a kid I was way too fearless. Though I'd lecture others. ('Cause, you now, they weren't as smart as me.) But I'd do really dumb stuff.

Hi

I worked, as a teenager, in a test department of a company that made switch gear ranging from the 660v dc for the London Underground to 25KV for industrial power switching. The test equipment was antiquated, especially the 660vdc that was produced by a motor/generator and was a wall full of lethal knife switches and live terminals everwhere. Touch the live part of the knife switch and the only fix was a flying rugby tackle to knock the guy off it... just touching him would transfer the shock to you.

That place had a concrete floor and you had to stand on 1/2" thick rubber mats and have one hand always in your pocket... these were low impedance lethal voltages.

I've had shocks that would have killed me but for the rubber mat or (later) the rcd ground current detector. Every home and business should have these.

[peeder]

Originally Posted by Geoff_T

Hi

I worked, as a teenager, in a test department of a company that made switch gear ranging from the 660v dc for the London Underground to 25KV for industrial power switching. The test equipment was antiquated, especially the 660vdc that was produced by a motor/generator and was a wall full of lethal knife switches and live terminals everwhere. Touch the live part of the knife switch and the only fix was a flying rugby tackle to knock the guy off it... just touching him would transfer the shock to you.

That place had a concrete floor and you had to stand on 1/2" thick rubber mats and have one hand always in your pocket... these were low impedance lethal voltages.

I've had shocks that would have killed me but for the rubber mat or (later) the rcd ground current detector. Every home and business should have these.

Actually the tackle is a bad idea too. If you can't reach the mains supply, the best thing to do is whack them off the current with a wooden 2-by-4. Yes, go ahead and break their arms if necessary, they will thank you later. Whatever you do you must avoid the dreaded Conga Line of Death where a succession of people try to pull each other off the current and are frozen as a result.

GFCI's are a fine idea, and in the USA are required by law in kitchens and bathrooms (those Test/Reset button outlets). I don't use them on audio myself but only because I haven't tested them in practice as to whether they will trip in the middle of a golden take or not...though if gear is tripping them maybe it needs a look.

50/60Hz AC was a terrible mistake...it's precisely the wrong alternator frequency for the heart to survive electrocution...and Edison was so against it he invented the Electric Chair as a demonstration of the hazard.

[Geoff_T]

Originally Posted by peeder

Actually the tackle is a bad idea too. If you can't reach the mains supply, the best thing to do is whack them off the current with a wooden 2-by-4. Yes, go ahead and break their arms if necessary, they will thank you later. Whatever you do you must avoid the dreaded Conga Line of Death where a succession of people try to pull each other off the current and are frozen as a result.

GFCI's are a fine idea, and in the USA are required by law in kitchens and bathrooms (those Test/Reset button outlets). I don't use them on audio myself but only because I haven't tested them in practice as to whether they will trip in the middle of a golden take or not...though if gear is tripping them maybe it needs a look.

Hi

It didn't happen often... the test guys were very cautious... but the switch in question was the main isolator and hard to reach with the guy already holding it. I never saw the rescue but the test department chief explained that he had to do it a few times.

[nharmonic]

Thank you for sharing specifics from your personal experience on this issue! I have all too often taken electricity for granted.
What it does for me.
And what it can do to me (or my clients).
I will consider and respect it much more from now on.

[corworld]

I didn't mean to joke about lethal voltages, just trying to keep things in perspective. The original post was about a small project studio, not a 10,000 watt arena PA. About the tongue comment, of course I meant a 9-volt. Are we that paranoid to think anybody is going to put their tongue on a car battery because they read it on the internet? I work with tube amps everyday so yes, I practice the one hand in the pocket rule as well as the rubber mat or rubber-soled shoes rule.

As long as we're trading high voltage stories, last year, a guy from around here were electrocuted when he tried to tag a 115,000 volt transformer with graffiti. He had third degree burns over 80 percent of his body. Definite Darwin Award nominee.

[hduncan]

Great responses thus far. I will definately excercise more caution from now on.

Originally Posted by corworld

Uh yeah, you are causing the speaker level voltage to conduct through your body to the guitar cable. It is not going to hurt you as it is probably only 12 volts or so but I wouldn't change speaker cables with everything on. Stick your tongue on the terminals of a 12 volt battery. Does it feel the same? Why aren't you using TRS cables with your monitors?

A. Yes its like a 9volt tingle
B. I'm using TS because the Duet outputs unbalanced signal

I don't think I should be getting shocked at all.... Do I maybe have a bad ground somewhere?

[hduncan]

So not only is that shock happening, when I plug my external monitor into the laptop, really loud noise happens. I am talking it sounds like there is some whine + someone constantly rapidly crumbling paper and a strange buzzing happens when I move my mouse or use the touchpad. THis also happens when I plug in my external MIDI controller...

I think I have a bad ground somewhere... all of my gear is plugged into one surge protector and into one outlet. one of the outlets plugs is one that is controlled by a lightswitch (so you can plug a lamp into it and turn it on always and then use the light switch to flow power or not)

ANY IDEAS?!?!? This sucks!

[Geoff_T]

Originally Posted by DarkEcho

So not only is that shock happening, when I plug my external monitor into the laptop, really loud noise happens. I am talking it sounds like there is some whine + someone constantly rapidly crumbling paper and a strange buzzing happens when I move my mouse or use the touchpad. THis also happens when I plug in my external MIDI controller...

I think I have a bad ground somewhere... all of my gear is plugged into one surge protector and into one outlet. one of the outlets plugs is one that is controlled by a lightswitch (so you can plug a lamp into it and turn it on always and then use the light switch to flow power or not)

ANY IDEAS?!?!? This sucks!

Hi

A rather obvious question... Is the power outlet that's controlled by a light switch using a dimmer switch for the wall switch?

Second obvious question... Have you tried it without the surge protector (which might be broken)?

I'm amazed that you are still using this set up without calling in a qualified electrician.

tutt

[nosebleedaudio]

I would get a VOM and see how much voltage there is, if you don't already own one, get one.
I assume your main surge protector is plugged into a confirmed grounded outlet...
I would NOT lift AC ground on anything, lift the audio ground..
I know one of many stories like this; an engineer buddy of mine told me he had a band in recording and using an old Hammond and Leslie, NOT grounded, the keyboard player grab a mic that was grounded and got knocked off the piano stool...
Was not funny at all, esp. to the engineer...

[Geoff_T]

Originally Posted by nosebleedaudio

I would get a VOM and see how much voltage there is, if you don't already own one, get one.
I assume your main surge protector is plugged into a confirmed grounded outlet...
I would NOT lift AC ground on anything, lift the audio ground..
I know one of many stories like this; an engineer buddy of mine told me he had a band in recording and using an old Hammond and Leslie, NOT grounded, the keyboard player grab a mic that was grounded and got knocked off the piano stool...
Was not funny at all, esp. to the engineer...

Hi

Good suggestions and my point about the light dimmer is that he may be sending an asymetric or distorted ac signal to his gear and causing the odd noises.

I would not use any equipment there until it was established as safe by someone qualified to do so... volts jolt, mils kill, etc.

[newfuturevintage]

Originally Posted by DarkEcho

Great responses thus far. I will definately excercise more caution from now on.

A. Yes its like a 9volt tingle
B. I'm using TS because the Duet outputs unbalanced signal

I don't think I should be getting shocked at all.... Do I maybe have a bad ground somewhere?

correct. you shouldn't be getting shocked at all, and you probably have a bad ground, and / or something amiss in the gear you're using.

First thing I'd do in your place would be to get something like this:
Amazon.com: Electrician's Best Friend - Instant Outlet Circuit Tester - Lighted Indicators: Home Improvement
and plug it into the wall outlet where your power strip is plugged in to see if you have a valid ground connection. Actually unplug your power strip, and put this where it was. If you don't have solid ground, stop. Call an electrician, and get one put in. Might be a cheap fix, might be expensive, but what you have now is dangerous and unacceptable.

If it's OK, return your strip to its outlet with everything else unplugged from the strip. Plug the tester into the strip. If the strip is faulty, replace it.

If both the strip and the outlet check out OK, the next possibility is that you have a piece of defective equipment, my first guess would be one of the powered monitors as these are the only things with high voltage going inside their chassis (the Duet is bus powered, the laptop should only be getting ~18Vdc from its brick). I'd try measuring for AC between guitar plug ground on the Duet and metal on one of your monitors (with the VOM), with only one monitor connected to AC at a time to see if one presents itself as the culprit. If you're not comfortable with doing this, hire someone who is licensed.

As for the noise from the external monitor, I'm less worried about that: my suspicion is it's switching noise from the power supply (laptop or monitor) or from the video card getting into the duet via the data connector's ground. This is a pretty common issue with ungrounded / bus powered soundcards connected via USB or Firewire. It's usually solved by isolating the soundcard from ground (1:1 transformers in-line to the audio monitors or ebtech's hum-x on the AC for switch mode power supplies are two possibilities)

[hduncan]

Ok everyone, thanks for the responses thus far.
First of all, there are no dimmer switches in this house, but the bottom socket of the outlet that my stuff is plugged into is setup to be turned on or off via a light-switch. The noise is present when the strip is plugged into either one.

Did I mention that the noise gets louder if I UNPLUG the laptop? The same is true if I unplug the power cable from one of the monitors, the volume of the papery noise/whine increases when one of the monitors is unplugged, almost like there is one less ground path and the noise has no where to go but out the speaker cone!

I used a circuit tester to test for faulty wiring of the outlets. The outlets checks out to be wired correctly, so I checked each socket on the power strip, those all checked out fine as well. Im not totally clear on what I should do now as far as testing each peice of gear, as most of the gear I am running is necessary to recreate the noise I hear in the speakers...

newfuturevintage, you said to test for AC at the monitors? can you go into more detail about this? thanks!

Also, the noise that happens when I plug in the external monitor is the same noise I get when I plug in my MIDI controller via USB.

[uncle duncan]

Have you tried running a heavy-duty extension cord from a different outlet? It could be there's an appliance or something plugged into the circuit you're using, causing funky AC.

One thing I did was run a new 'floating ground' from my outlet. You disconnect the green ground wire from the third leg of the outlet and run a new green wire to the ground stake outside. If you have an attic or crawl space, you can route it to the outlet that way. Then you run everything in the studio off of that one outlet, just like you're doing now.

A little OT: You can create ground loop problems by plugging gear into two separate circuits and then interconnecting the gear. This happens a lot on DIY gigs in crappy venues. The PA is on one side of the stage, the keyboard rig is on the other side. I make a habit of running an extension cord over to the AC outlet the PA is plugged into, which eliminates the ground loop problem when DI'ing the keys into the PA.

[peeder]

Originally Posted by uncle duncan

One thing I did was run a new 'floating ground' from my outlet. You disconnect the green ground wire from the third leg of the outlet and run a new green wire to the ground stake outside. If you have an attic or crawl space, you can route it to the outlet that way. Then you run everything in the studio off of that one outlet, just like you're doing now.

I think that may actually be illegal...grounding has to pass muster with the city electrical inspector. If not illegal, it could easily be used by an insurance company to deny a claim...and the claims could be ruinous.

People, please don't fool around with electricity. People always instantly point to ground when they hear or feel something, but the service is often fine, and their wiring topology is often pitifully stupid or at least overambitious.

No one unable to diagnose and fix a ground loop in an audio rig should even DREAM of playing with service. tutt

[hduncan]

I got an extension cord and ran it to a different outlet. I plugged the surge protector into it and the noise remains.

I then unplugged everything and plugged each monitor and the laptop brick into the extension cord- clean: no noise (but of course, the flatpanel isnt plugged in, so)

I swapped the laptop with the flatpanel and the noise resumed.

Then, to make sure that the surge protector isnt broken, I removed everthing from the surge, and use the extra spots on the extension cord and plugged everything directly into the wall- still noisey

the only time I got something other than the screechy papery noise was when I moved the monitors via the extension cord to another rooms outlet and then I got what I think was the 60hz humming, which I assume is a ground loop.

...I am at a loss guys.. I cant figure this one out. I'm no expert but from the what I've been testing, it seems like the power in the house is fine. I want to blame the flatpanel, but the same thing happens when I plug in the MIDI controller via USB. Everything seems to be fully and properly grounded so I dont know why I am getting this whiney noise. another thing to mention- I believe that back when I used TRS cables, the noise was significantly quieter. when I switched to TS it got much louder. Don't know if that is a clue that will help or not.

Would uploading a recording of the noise help?

*NOTE* Just noticed something else: The noise ceases when the laptop is turned off. Turning the flatscreen on and off has no effect.

Furthermore- The noise starts even when the outer metal of the flatscreen DVI cable touches the DVI port shell, and transfers to the monitors even if the Duet firewire cable is only touching via the metal casing of the connector. Touching the DVI connector metal to the firewire casing does not reproduce the noise...

I think the noise is generated by the laptop... Any ideas to further test this? It also makes a weird noise when I use the touchpad... its starting to seem more like the laptops fault.

And here is the best part: When I put the macbook to sleep, the noise significantly gets quiet, but there is a quiet, slow, pulsing noise that rises in frequency with the macbooks pulsing LED (it pulses when the laptop is in sleep mode.)

[LewisWu]

Originally Posted by peeder

the dreaded Conga Line of Death

LMAO... i've always imagined how it would look... but the dreaded conga line of death sums it up perfectly

[Geoff_T]

Originally Posted by LewisWu

LMAO... i've always imagined how it would look... but the dreaded conga line of death sums it up perfectly

Hi

When I was a schoolkid (back in the late 1950's) our science teacher had us all hold hands and then hold the wires coming from a coil wrapped around a large horseshoe magnet... he was demonstrating the properties of back emf... the principle car coils work on when the contact breaker opens (pre cdi ignition)... and when he removed the keeper from the poles of the magnet we all flew across the room at high speed. Amazing that nobody was concussed!

The same science teacher had a Darwin moment when showing us the heating properties of electric current by holding a thin bare wire in his hands and slamming it down onto a 12v car battery... red hot wire... giant arcs/sparks... smells of burning flesh and many foul oathes and curses from the teacher!

[Geoff_T]

Originally Posted by DarkEcho

*NOTE* Just noticed something else: The noise ceases when the laptop is turned off. Turning the flatscreen on and off has no effect.

Furthermore- The noise starts even when the outer metal of the flatscreen DVI cable touches the DVI port shell, and transfers to the monitors even if the Duet firewire cable is only touching via the metal casing of the connector. Touching the DVI connector metal to the firewire casing does not reproduce the noise...

I think the noise is generated by the laptop... Any ideas to further test this? It also makes a weird noise when I use the touchpad... its starting to seem more like the laptops fault.

And here is the best part: When I put the macbook to sleep, the noise significantly gets quiet, but there is a quiet, slow, pulsing noise that rises in frequency with the macbooks pulsing LED (it pulses when the laptop is in sleep mode.)

Hi

I suspect that there may be a problem with the power supply to your Mac... you ought to get it checked out.

[hduncan]

I have a buddy with an almost identical version of my MBP. His is a little newer . Ill see about getting him out this weekend to swap out my backbook with his and see if the noise persists. If so, I will try out a regular MacBook, and possibly a PC laptop of some sort to try and rule out any laptop related disfunction.

Until then, I will try swapping out the power brick with one from another macbook tonight to see about the power supply being the cause.

I'm also gathering a spare DVI cable, and I have another LCD Flatpanel that I will try plugging in to gather more observational data.

Any other ideas of things to test while i'm at it?

the only thing I dont have a spare for is the Duet.. I dont have another audio interface at the moment... maybe if everything else fails to draw conclusions, I can buy something comprable to the Duet at GC, test, and return it.

Thanks for the help so far everyone! I think I am a few steps away from identifying the source of this HORRIBLE noise.

[LewisWu]

Originally Posted by Geoff_T

when he removed the keeper from the poles of the magnet we all flew across the room at high speed

oh man, that sounds like a fun science class.. the closest i ever got to something like that was watching my highschool physics teacher blow a fuse out on the terminals in the lab.. it was bright, but it didn't last that long, so the exhileration was short lived.. nothing like flying across the room

[rjacobsen]

I would try running the laptop on it's battery and not using the ac adaptor. If the noise persists, I would assume something is wrong with the laptop. If you don't get any noise, then I would assume the ac adaptor is defective. Have you tried listening to any audio on the laptop through it's headphone output with nothing hooked up to it? Have you tried just hooking up any other source to your monitors to see if you get a noise? Also try and use the headphone out of the laptop and hook that up directly to your monitors, if you have the adaptors to do it. I hope these suggestions help you out!!
rjacobsen

[Geoff_T]

Originally Posted by LewisWu

oh man, that sounds like a fun science class.. the closest i ever got to something like that was watching my highschool physics teacher blow a fuse out on the terminals in the lab.. it was bright, but it didn't last that long, so the exhileration was short lived.. nothing like flying across the room

Hi

An aquantance of mine, with a sadistic sense of humour, wired a bell push to the reception desk of the company he worked for, wired across the 240v supply and via a 13A fuse in the plug.

He then put a warning notice next to the button proclaiming that the bell was broken and not to push the button.

He didn't have to wait long before someone pressed it and damn near vapourised the push button switch!