Hum with two amp set-up

Eric West · Post by **Eric West** » 18 Dec 2004 3:14 pm

Yup. You're right b0b, as you often are.

Unless you're dealing with monster voltage, the human body will not carry enough current to light the smallest of light bulbs. Given that your heart is run by microvoltage, though, people can screw around with it at their own peril.

When I was a kid, we used to play "electric fence" games, and a couple of us got to where we could hold onto it without jerking or grimacing to show the "victim kids" that it was "off".

When in the military as a 5 level electrician, I got to where I never used a voltage tester unless it was three phase. Less error. I could, and can today, hold onto a 110 line with no ill effects while well grounded, and touch the 220 side to check for it, though not firmly. It is something that you build up a tolerance to. Even from one hand to the other, through the trunk.

They say that repeated exposure can cause mental problems, but I've never noticed any that I can't blame on something else....

Anyhow, in summary.

Just because you plug a three prong connector into a three prong outlet, doesn't mean that it is "grounded".

Trust, but verify.

EJL

Ken Fox · Post by **Ken Fox** » 18 Dec 2004 5:19 pm

Just some good reading from the net:

Offhand it would seem that a shock of 10,000 volts would be more deadly than 100 volts. But this is not so! Individuals have been electrocuted by appliances using ordinary house currents of 110 volts and by electrical apparatus in industry using as little as 42 volts direct current. The real measure of shock's intensity lies in the amount of current (amperes) forced though the body, and not the voltage. Any electrical device used on a house wiring circuit can, under certain conditions, transmit a fatal current.

While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA(0.1 to 0.2 amp) are lethal.

Currents above 200 milliamps (0.2 amp), while producing severe burns and unconsciousness, do not usually cause death if the victim is given immediate attention. Resuscitation, consisting of artificial respiration, will usually revive the victim.

From a practical viewpoint, after a person is knocked out by an electrical shock it is impossible to tell how much current has passed through the vital organs of his body. Artificial respiration must be applied immediately if breathing has stopped.

Note that voltage is not a consideration. Although it takes voltage to make current flow, the amount of shock-current will vary, depending on the body resistance between the point of contact.

Shock is relatively more severe as the current rises. At values as low as 20 milliamps, breathing becomes labored, finally ceasing completely even at values below 75 milliamps.

As the current approaches 100 milliamps, ventricular fibrillation of the heart occurs - an uncoordinated twitching of the walls of the heart's ventricles.

Above 200 milliamps, the muscular contractions are so severe that the heart is forcibly clamped during the shock. This clamping protects the heart from going into ventricular fibrillation, and the victim's chances for survival are good.

Danger - Low Voltage
It is common knowledge that victims of high-voltage shock usually respond to artificial respiration more readily that the victims of low-voltage shock. The reason may be the merciful clamping of the heart, owing to the high current densities associated with high voltages. However, lest these details be misinterpreted, the only reasonable conclusion that can be drawn is that 75 volts are just as lethal as 750 volts.

The actual resistance of the body varies depending upon the points of contact and the skin condition (moist or dry). Between the ears, for example, the internal resistance (less the skin resistance) is only 100 ohms, while from hand to foot is closer to 500 ohms. The skin resistance may vary from 1000 ohms for wet skin to over 500,000 ohms for dry skin.

Buck Dilly · Post by **Buck Dilly** » 19 Dec 2004 10:48 am

Get a local tech to help you with ground problems. These problems can be very complex. Take advice from qualified technicians only. Be careful giving advice with regards to 118 volts devices, unless you are willing to accept the consequenses of such advice. I have had many mysterious ground hum problems, some of which have taken out racks of expensive gear. At times these were tha faults of the rooms I was playing (old NYC clubs, old hotels etc), and at times it was my own lack of prudence.

CrowBear Schmitt · Post by **CrowBear Schmitt** » 19 Dec 2004 2:11 pm

This subject has been brought up before has'nt it ?
how often do we take for granted the electrical installation that we plug into ?

Well guys, you'll have to add a Ground tester in your pack a seat so you can test the electrical system of the joint you'll be playing in or check w; the house electrician if there is one around.
the Ground Fault Breaker is compulsory in todays Electrical installations.
30mv
it's rare that they aren't installed next to the breakers (or fuses) in the cabinet
even the main breaker from the power company is a ground fault breaker but set to kick in at around 500mv
in order for them to work properly, the Earth must be connected & measured for the correct resistivity
anywhere between 10 and 100 ohms for the Earth will do
No Earth ? the fault breaker won't do his job
remember how easy it was to toss the hair dryer in the tub when you found your wife & your best friend in it ?
nowadays with a proper electrical installation, they will be unharmed cause the 30mv ground fault breaker will shut the power off
as an electrician, i have 2 testers that permit me to measure the Earth and test the Ground fault breaker.
Bands appreciate that

a question for Ken : here in Europa we use 220v and 50 cycles<----i believe
is there a diff between 110 and 220 and cycles here compared to the States ?
i have'nt noticed ground hums from using 2 or more amps together
the ground potential is the same in all the gear
we just make sure not to plug in w; the lights and their faders
[This message was edited by CrowBear Schmitt on 19 December 2004 at 02:21 PM.]

Ken Fox · Post by **Ken Fox** » 19 Dec 2004 3:17 pm

Typical here is 120VAC at 60 hertz (cycles) per second.

Brad Sarno · Post by **Brad Sarno** » 19 Dec 2004 3:35 pm

Do a google search for Neil Muncy. He's sort of considered god of all things related to a/c power in the audio world. He's the guy who's authored a number of AES documents on the subject. He also works now for Surgex, perhaps the very best in studio power conditioning. He's a genius in this world of inductive ground loop voodoo.

Brad Sarno

Stephen Gambrell · Post by **Stephen Gambrell** » 19 Dec 2004 7:35 pm

Two REALLY scary posts, here. David donald's "advice" to flick one's hand against the back of an amp, while touching a mike, or some other piece of suspect gear---I would no more show up at a gig without a meter, than spare strings. This is the kind of advice that leads to the musicians' friends playing a benefit, REAL SOON.
And Eric, if you want to ground yourself, while grabbing 110---as a "5 level" electrician, did you learn Ohm's law? This is another benefit in the making!
Guys, if there's a doubt about a missing ground, neutral in the wrong place, disconnecting a ground to stop a loop--PLEASE, use:1. a good voltmeter.
2. some common sense.
Repeat step 2 as often as necessary.

Eric West · Post by **Eric West** » 19 Dec 2004 8:16 pm

Well, people scare or worry themselves to death more often than get killed by playing guitars with no grounds.

Now it seems you can get killed changing the battery in your tuner....

People plugging three prong plugs into three prong receptacles with no thought to whether they are actually properly grounded outlets in spite of all the admonitions to the contrary, are a more worrisome lot.

It's an easily avoided problem with a simple tester.

Besides, fate lets a precious few enter the pearly gates doing something we love to do.

Why decrease the odds, unless you have some reason to doubt your entrance..

I never plug my amps into "grounded" outlets.

I test for 110 by hand.

I don't care what other people do.

Some of them are indeed smarter than I, and some probably dumber.

I've lived through more than a couple thousand gigs thataway. More booked in the future, God willing.

Done a damn lot of house wiring too.

My house for example has ALL the outlets grounded and GFIs on ALL downstairs, outside and bathroom receptacles. My computer is on a dedicated separate line. I did it all myself IAW the '96 NEC and had it duly inspected.

I still don't use three prong plugs on my amps.

EJL[This message was edited by Eric West on 19 December 2004 at 08:23 PM.]

Stephen Gambrell · Post by **Stephen Gambrell** » 20 Dec 2004 6:08 am

"I still don't use three prong plugs on my amps."
Then what are you gonna do when, at one of those THOUSANDS of gigs, some electrician/plumber/house painter has put the black wire....
Oh, never mind. I'm probably one of the "dumber" ones.

MERRY CHRISTMAS, Y'ALL!!!

Eric West · Post by **Eric West** » 20 Dec 2004 7:05 am

Well, Steve, now that you mention it...

EJL

PS Merry Xmas.[This message was edited by Eric West on 20 December 2004 at 08:05 PM.]

Gary Preston · Post by **Gary Preston** » 23 Dec 2004 1:15 pm

I agree with Ken Fox . I had the same problem with two amps . Try the little box that Ken and i did and you will find your answer . Thanks , Gary .

Louie Hallford · Post by **Louie Hallford** » 24 Dec 2004 5:14 pm

Thanks Mr Fox for your post . I have sent 45 + years in the electrical utility business about half of it in the safety business. My training including certification to bare hand 138KV and 345KV transmission lines. I have found that the gory burns are the high voltage burns, but notice that the 30% of fatally injured who die of low voltages always seem to be just as dead.

Anyone who disregards the dangers of house hold voltages,even 110 volts is shooting dice. Your comments regarding milli amps being fatal is right out of the book.

Stephen Gambrell · Post by **Stephen Gambrell** » 24 Dec 2004 6:47 pm

Mr. Lundgren may disregard those posts bt Mssrs. Hallford and Fox.

Eric West · Post by **Eric West** » 24 Dec 2004 9:41 pm

Let your mind wander a bit.

Look at your christmas tree.

Don't touch it.

The lights are probably not grounded.

Better yet...

Naw....

Merry Xmas.

EJL[This message was edited by Eric West on 24 December 2004 at 11:47 PM.]

Stephen Gambrell · Post by **Stephen Gambrell** » 24 Dec 2004 11:48 pm

Sorry, Eric---I enjoy your posts too much to wish electrocution on you. So try a meter---no one will think you're a wiener, and I don't mind being included in your "dumb" categorization.
And I haven't had a Christmas tree, with lights, since back in '83, at a Christmas party, BEFORE I quit drinking, when I decided the tree needed watering...
Never mind.

No one's attacking you.

Fox News got the conspiracy thing all wrong.

Enjoy your gig.

I'm enjoying rehab.
Shall we visit the "depression" thread again?

Merry Christmas, from my house to yours.

If I were Hunter S. Thompson, I'd end this cleverly...

If I only THOUGHT I was Jack Kerouac...[This message was edited by Stephen Gambrell on 24 December 2004 at 11:49 PM.]

Eric West · Post by **Eric West** » 25 Dec 2004 12:50 am

Well I thank you Mr G I think.

BTW over on the
Forbidden Zone, Marty found this guitar player from SC named Terry Couch, that is phenomena. phenmon.. well.. he's good anyhow, and he wondered if you'd heered of him.

The only meters I've got are my old Wiggins that doesn't show proper grounding, and I've got a cheap digital that I don't trust.

Two prongs for me.

Just like your UL christmas tree.

Oh, and I've read EVERY word HST published in his books, and for the life of me I can't figure out where he lost his mind. He's completely off his nut. Looking back on my own life, it's hard to figure where I lost most of mine.....

Merry Xmas.

Don't put any watch batteries in your bodily orofices. They heat up, and if in your ear, can breach the blood brain barrier, and you know... well... it's not a pretty picture.

I wear earplugs so nobody sneaks up and drops one in there when I'm sleeping.

A person can't be too careful..

Merry Xmas.

EJL

Ken Fox · Post by **Ken Fox** » 25 Dec 2004 10:24 am

When you ask most people why equipment is grounded they have no idea! It is simple, life safety. If a hot wire goes to the chassis of an amp, the chassis is a life threat. If the chassis is grounded, the circuit breaker will disconnect. Due to high body resistance, most 120VAC shocks are not fatal. Having been a licensed journeyman electrician for 24 years in Oregon and Washington I have had a chance to learn quite a bit on the subject. Most people do not realize that death from a lot of high voltage shocks (especially 277 VAC) happens hours later. The heart rhythm is upset by such a shock. Later on in the day you just drop over dead! It was a requirement in Local 48 that you went to the cardiac unit for testing after a shock. The heart rhythm could checked for potential problems and then proper lefe saving action could be taken.
As Eric mentioned earlier you have no idea if the place you are playing was wireed correctly. Your best defense in a portable GFCI device (Home Depot, extension cord with GFCI attached). A GFCI will work on even a two-wire, ungrounded system. Code requires any ungrounded 2-wire outlet in a residence be replace with a GFCI outlet. Also a simple plug-in tester with neon lights is always a good idea to carry on the gig.

Dan Tyack · Post by **Dan Tyack** » 25 Dec 2004 11:27 am

I test for 110 by hand.

And you get some free electro shock therapy, to boot!

------------------
www.tyack.com

Eric West · Post by **Eric West** » 25 Dec 2004 11:32 am

Amen Ken. I haven't meant to seem callous, but I've often gone into the broom closet of places I've played and seen uncovered breaker boxes with stuff piggy backed all over the place and grounds tied to neutrals, or at least "white wires". I'd rather take my chances on mot energizing my amp through the case. Before I took my third tooth off twenty years ago I used to pop filter caps for some reason in my 500. After I did, I never popped another. Probably not connected, but hey...

Used to run a 3ph resaw in Townsend MT in the 70s, and when the saw water got sprayed around you could get knocked on your ass when changing blades if you leaned into the control box or put your shoulder on the motor while grabbing the wet bare arbor. We never knew "why". I was working cheap. It had a "Delta" 277 "wild leg", and I know why they called it that. I got hit by it more than once. Luckily not through the trunk.

I haven't liked "testers" since one of my buddies in the AF "tested" a box with his new digital meter, and got a false reading, then dropping a screw onto the main bus, blowing the whole works up in his face.

I DIDN'T know that they have GFI boxes like you said that work on two wires.

THAT's the ticket. No doubt about it. That and a neon plug tester. They're pretty cheap.

Hope you are liking your new area.

Still raining, drizzling etc up here.

Sunday Jams at Jollies are pretty dead without Kevin and Ray.

Merry Xmas.

EJL

Eric West · Post by **Eric West** » 25 Dec 2004 2:01 pm

Yeah well Dan, nothing's free.

They say that electroshock therapy for those that volunteer for it is just an addiction, and not clinically effective.

Huh Steve..

JUST KIDDING!!!!

EJL

Ken Fox · Post by **Ken Fox** » 25 Dec 2004 5:09 pm

I thought I had seen it all till I moved down here! Hot tub wired to a 50 amp breaker with # 10 wire. Breakers for the pool and hot tub added by "fly-by-night" contractors were the wrong brand and a poor fit at best. The genius that installed the hottub failed to moved the current limiting jumper to 30 amps, so the tub could draw full tilt on #10 wire (30 amp wire, folks). Well one hot legs was burned clean of the terminal at the tub from overheating and a loose connection!

Like Eric said, you can't always trust your local electrican had any proper training or did things to code! I had a friend that fried a Hammond B-3 at a gig. The duplex was wire for 240VAC, not 120VAC. You never know. It ain't always a "duck" just cause it looks like duck, walks like a duck.....

Joseph Barcus · Post by **Joseph Barcus** » 25 Dec 2004 6:14 pm

i got hit by lighting two years ago, im afraid if i would have had the ground lifted on my stuff I would not be typing this today, lose connections can also cause hum. maybe lose in the plug itself you wont be able to see it, but heck a new end dont cost that much if you cant find anything else lose, same as in your home you see lights dimming down when something starts well a large amount of people dont know that that is also a lose ground. well anyways i agree about not ever lifting grounds. just my 3 cents worth

Ron Randall · Post by **Ron Randall** » 25 Dec 2004 8:37 pm

Uh Duh. I have a neon bulb, two lead tester. How do I use it to avoid these problems?

Eric West · Post by **Eric West** » 26 Dec 2004 9:48 am

Well, I think I know the older pocket clip type tester you are talking about, and it's mostly for testing hot to neutral or hot to ground.

Here's
the type I mean for testing the grounds in three prong outlets.

This Site seems to have the best information I could find in a short time.

No sense in worrying yourself into paralysis about it, but it's worth considering everytime you plug into a strange outlet.

Kind of like dating these days...

EJL

Ken Fox · Post by **Ken Fox** » 26 Dec 2004 10:00 am

With the neon tester you will find 220VAC is of course brighter. On a properly wired 120VAC duplex outlet plug, the small blade is hot, the large blade is neutral. A test between these two should light the bulb. A test from the outlet ground to the hot terminal should also light up. Now why is that? That is because at the typical home service panel all neutrals (now referred to by the National Electric Code as the "grounded conductors) are tied to a bus bar that is bonded to the ground bus bar.