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Author
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Topic: Ground Lifting
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Lee Baucum
Member From: McAllen, Texas (Extreme South) - The Final Frontier
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posted 13 June 2004 01:56 PM
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Back in the old days, Jeff Newman convinced us that we should be playing through two amps. He warned us that we had to lift the ground on one of the amps, or we would have a terrible hum. He also warned us not to lift the ground on both amps, or we could be electrocuted. Nowadays, there are so many configurations. Some folks use a few rack-mounted devices that are used between the guitar and amp or amps. Some patch that rack into the f/x loop on the amp. Other folks have everything mounted in a rack, including the pre-amp and power-amp. I've always been told that we need to have at least one device hooked up to ground, and everything else will be grounded through the use of shielded cables linking everything together. Is this really good enough? There are so many variables. How does one know they are protected from a potentially fatal shock? ------------------
Lee, from South Texas
Down On The Rio Grande |
C Dixon
Member From: Duluth, GA USA
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posted 13 June 2004 02:21 PM
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Lee,You are a man after my own heart. Oh man! Folks I cannot tell you how important it is that every metal part that is in your rack (or setup) be grounded. Now this does NOT have to be a direct ground. But all have to have a connection to ground, even if indirectly. Connecting cable grounds can cover this in most cases. Sadly it goes deeper than this. And Jeff is very right about being electrocuted. IF you have any AC power line electrical device NOT connected to ground, and you are touching ground in ANY way and you touch that device, YOU can be killed! In other words let's take two amps. One is got the plug grounded. The second one you cut the ground lug or use one of those plug adaptors. Now if you touch the first amp and you touch the second amp you are apt to get across the full AC voltage that is being supplied by the electrical outlet, If that second amp's ground is not connected to the first amp's ground in some way. This is why before you plug anything into the wall, connect all the cables so that EACH device is grounded thru those cables back to the device that will be plugged into the wall. NO HUM or buzz ever been is anywhere near as bad as the loss of your life. PLEASE! I KNOW from whence I speak, carl |
Ken Fox
Member From: Ray City, GA USA
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posted 13 June 2004 02:27 PM
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Lee, I just bought a new device by Ebtech called the HUM-X and it works! Safely grounds the amp right at the cord and eliminates hum. Only one needed for one of the amps. They are about $59.00 at Musician's Friend and worth every cent I spent! |
CrowBear Schmitt
Member From: Ariege, - PairO'knees, - France
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posted 13 June 2004 03:10 PM
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having a ground is essential for safety
how often do we take it for granted that the Ground we are pluggin' into is efficient ?
as an electrician, i have a deepvice that measures resistivity of the earth (or ground) in an installation which permits me to know if it's good or not (ohms)
there is also a safety trip deepvice(in french it's differential breaker30 ma)in electrical boards that will shut the power off if there is a fault current in contact w: the user
in the old days, it was easy to do away w; a cheatin' husband when he was in the bathtub w: a cutie by chuckin' the hair dryer in w: 'em
in present day electrical set ups it don't work that way anymore
just to say, that i check the system i plug into so i know it's safe[This message was edited by CrowBear Schmitt on 13 June 2004 at 03:12 PM.] |
Larry Clark
Member From: Herndon, VA.
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posted 13 June 2004 04:05 PM
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While spending many years working in the retail music industry I've heard horror stories about bands playing in clubs and plugging into what appeared to be standard 3 prong wall outlets only to find out later the ground wasn't connected or worse some Bozo had wired it up to 240. You can purchase an inexpensive tester at most home improvement and hardware stores. It could save your gear and more importantly your life. |
Paul Osbty
Member From: Seattle, Washington, USA
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posted 14 June 2004 02:10 AM
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I've never had the troubles described above, but I also have seen most of the schematics of my equipment.With the 2 amplifier scenario, it would seem to me that the ground/chassis is being tied to one side of the transformer secondary, instead of the center tap. Most all of my equipment has the chassis tied to the center tap. This gives a negligible amount of AC on the chassis. So, as I read it, if a 2-prong adapter was used (in the 2 amp scenario) there is 115 VAC on the chassis? Is this something a UL listing would allow?[This message was edited by Paul Osbty on 14 June 2004 at 02:12 AM.] |
Buddy Griffin
Member From: Derwood, Maryland, USA
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posted 14 June 2004 05:36 AM
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I carry a cheap (and small)l.e.d. radio shack ground tester with me and check the wiring at the gig site for bad grounds, etc. I have found problems many times at certain outlets, especially at outdoor events with temporary wiring. |
Lee Baucum
Member From: McAllen, Texas (Extreme South) - The Final Frontier
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posted 14 June 2004 06:23 AM
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Here is the reason for starting this topic.Click Here Buddy, I have one of the little devices also. I won't plug in anything until I check the system for wiring problems. ------------------
Lee, from South Texas
Down On The Rio Grande |
C Dixon
Member From: Duluth, GA USA
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posted 14 June 2004 08:02 AM
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Paul,UL would NEVER approve of removing grounds or using an adaptor plug; hum or no hum. When we clip the ground lug or use an adaptor, we are in the minds of the entire elecrical world including UL, commiting a no-no. But if one MUST do it (and it takes that to get rid of hum I agree) then by all means make sure that at least one "device" IS connected to ground at the AC outlet; and that ALL other devices are grounded thru cables or straps (or something) to "that" device! Dangerously high electrical charges can rise on ANY piece of eletrical equipment if that device is not held at ground potential reference. Again, this should NOT be taken lightly. Your life is at stake, carl |
C Dixon
Member From: Duluth, GA USA
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posted 14 June 2004 08:18 AM
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One final comment. The best way to be sure, is to perform the following test:With everything plugged in (including AC power) and with every device in the off position, use an ohmeter (a cheap one is fine) and with one lead touching the center screw terminal on the mounting AC wall plate, use the other lead measuring the metal part on every device in your setup. IF you do not get zero ohms on one or more devices... STOP! INVESTIGATE! CORRECT IT! BEFORE.... you turn the equipment on. "A stitch in time, saves nine" AND it also can save lives! Incidently the above test will spot even broken ground wires in the power cord as well as connecting cables, as well as ground connections back at the AC panel (if the panel was installed after 1980). About the only thing it won't check is whether the AC panel IS properly connected to earth grounded outside the building. But that is almost assured with the modern building electrical codes. The National Electrical codes have gone through rigorous and detailed refinements over the last 30 yrs. And most electrical inspectors and state govening bodies rigidly enforce the NEC. carl |
Pete Burak
Member From: Portland, OR USA
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posted 14 June 2004 09:25 AM
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Ken Fox showed me a test where you put put one lead of a meter on the faceplate of one amp and the other lead on the other amp, and use the ground switch to find the lowest potential.
What was the exact procedure for that Ken?
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Paul Osbty
Member From: Seattle, Washington, USA
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posted 14 June 2004 10:59 AM
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This is all good cautionary advice. I'm still not understanding how source voltage is getting to a chassis. |
C Dixon
Member From: Duluth, GA USA
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posted 14 June 2004 11:50 AM
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Paul,It's certainly NOT suppose to. However for any number of reasons it can and does. In most cases it is due to a malfunction in the device. But not always. Would you believe that RCA once built a TV set back in the 50's where one side of the two prong AC plug went to chassis? Well believe it; and that was the days before they came out with polarized plugs. Anyway, the test will show IF you are protected EVEN if there is a malfungtion. And IF there IS a malfunction that puts AC on the chassis (as oppossed to another chassis) AND they are all grounded through whatever medium, a fuse will surely blow. At least the AC circuit breaker will throw. Which is one of the prime reasons for the ground. Not the only one of course. thanks for asking, carl |
Jay Fagerlie
Member From: Lotus, California, USA
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posted 14 June 2004 12:56 PM
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Paul,
Remember before wall outlets had a small and large opening? (Non-polorized) The world was a "two wire" world, where taking two pieces of gear, plugging them in to a duplex outlet, you had a 50/50 chance that the two 'hot' and 'common' wires were connected to the power transformers of the two pieces of gear the same polarity. In just about every instance (I'm talkin' audio stuff here, folks) the way it was supposed to work is the hot goes to the primary high side, the common goes to the primary low side. The secondary low side is connected to chassis ground and the secondary high side goes to the rectifier (AC to DC conversion)
If for some reason, the wires are NOT connected like this, you WILL have your mains voltage potential between these two units, usually on the supposed 'ground plane' and here is where the danger lies. Modern polorized plugs are meant to make this a thing of the past.
And Carl, have you seen any of the 50's/60's practice amps that had NO power transformer? The high side of the power line goes through the heaters of the tubes in a serial fashion, through a limiting/matching resistor and then connects to common. The most DANGEROUS amps ever. Never use them when other powered equipment is around.
It's crazy what was sold as 'safe'......
Jay |
Ray Minich
Member From: Limestone, New York, USA
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posted 14 June 2004 01:13 PM
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quote:
Would you believe that RCA once built a TV set back in the 50's where one side of the two prong AC plug went to chassis?
A lot of 5 tube table radios in the '50s were the same way. They were known in the repair trade as "All American 5's". On the test bench we use a 1000 watt isolation transformer for this very reason. Without an isolation transformer, you work on a piece of equipment with one hand in your pocket. With an isolation transformer you can use both hands. A few years ago my dad was a plumber welding at a local refinery construction project. The electricians wired up a bank of huge welding machines the day before the welders were to begin. On the morning of the first day of construction welding, it had rained during the night. My dad noticed a dead frog at the base of the welder bank frame. Upon further investigation it was found that the electricians had wired one leg of 440 VAC 3 phase to the frame of the welder bank. Thank the man upstairs for the sacrificed frog, otherwise it would have been several pipefitterwelders including my dad.
Don't trust... Verify! |
C Dixon
Member From: Duluth, GA USA
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posted 14 June 2004 01:19 PM
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Yes I have Jay, I am sad to say, there is little I didn't see over the 40 yrs in the business. Some were tragic. Praise Jesus for the blessings of man being able to aquire knowledge. carl |
CrowBear Schmitt
Member From: Ariege, - PairO'knees, - France
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posted 14 June 2004 01:54 PM
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this is'nt answering the title of this post but it should help understanding the role of the Ground or Earth -
it was understood way back when that Earth or Ground was the solution for absorbing Lightning strikes and it's voltages.
the common Ground or Earth that we find in our present day installations became mandatory long after Leo made his amps and steels - so it's a recent novelty.
the purpose of Ground is to create a zone or volume where current can go when current is somewhere it should'nt be. that's a fault current(like in a chassis as Carl states) the common fuse or breaker won't necessarily protect you from that faulty current but that 30 milliamp breaker will ! that 500 milliamp breaker the power Co. set up w: the meter can too but not as quick as 30 ma !
these safety breakers will trip IF the resistivity of the earth is according to regulations (in France: minimum required is about 100 ohms - for lightning protection it's 10 Ohms)the less resistivity the better.
a fault current is'nt necessarily 110v runnin loose - it can simply be the + or Phase runnin'loose - a body will bridge that fault current w: the ground he's standin' on and it can just tickle or it can ZAP ! it could feel like an endless elevator ride to Heaven but in reality it's the cycles you feel passin' through your body  - if it's a proper installation this can't happen but if it is'nt well you better hope somebody's got a wooden broom handle to disconnect you from that fault current - having the proper ground and those 30 ma safety breakers are the keys to safety -
i don't know how it is in the US but i imagine it's the same as here - establishments that recieve public are controlled yearly by safety commissions so they've gotta have it right or they can't operate - BUT, once they've gone,a lot can happen in a year that can render an installation unsafe -
it is always wise to test if there is a ground in the plugs you're about to use - if there are those 30 ma breakers - check if there is a house electrician - keep your gear grounded ! Do not play yer Tele in a Twin barefoot in the grass but on a wooden stage - if and when a thunderstorm pops up: stop playing !
God Bless Benjamin Franklin, Thomas Edison, Leo Fender, Noel Boggs and the rest of ya's 
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Paul Osbty
Member From: Seattle, Washington, USA
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posted 15 June 2004 01:34 AM
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Good info. The legacy gear is something to be careful of. We had a Plush amplifier (done in blue-sparkle padding!) burn a transformer on us during a gig and catch fire. Exciting! Great for a bunch of drunk 20-somethings in the crowd.I recall a couple of occasions getting tickled on the lips from microphones, too. But, this was all years ago. I've either gotten rid of the gear or upgraded it. I do have one remnant keyboard from 1980, but it came with a 3-prong plug and I managed to get a schematic. |
Jennings Ward
Member From: Edgewater, Florida, USA
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posted 25 June 2004 08:15 PM
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Fellas, keep in mind that manufactures would not put ground connections on equipment if it were not necessary or required. Reason , Cost.. anyone that removes a ground wire is in plain words an IDIOT.. or they have a death wish. I have worked on everything from pocket radios to TV transmitters..And believe me,you had better protect your grounds, nice pun ,huh.... as all have said. DONT REMOVE GROUNDS. Find trouble. Would U rather save DOLLARS OR LIVES........ JENNINGS------------------
EMMONS D10 10-10 profex 2 deltafex ne1000 pv1000, pv 31 bd eq, + |
David L. Donald
Member From: Koh Samui Island, Thailand
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posted 26 June 2004 02:16 PM
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On strange stages with unknown ground characteristics, staying grounded is very solid advice.I was playing a raincoat and chicken wire gig, and they insusted you only use the house sound system, and even had the house electrician show up for new bands and drill a grounding lug onto amps...(un-asked) for any amp he couldn't ground to his satisfaction. With the general amount of beer the bands might wear this was prudent.
But I was rather pisssed to come back from dinner and see a guy with a electric drill putting a hole in my SVT bass amps chassis...
In the studio for recording some times you MUST use ground lifting... here's my favorite anecdote on the subject.
During a session set up, I told a guy who was making $125,000 a year fixing and designing electronic medical equipment, to put a "groundlifter" on a buzzing guitar amp...
that was sitting on top of a upright Steinway piano.
I came out of the control room and saw two pieces of 2 x 4 wood under the amp....
but the amp still on top of the piano!
5 feet in the air. I had to clock off 10 minutes of studio time to stop laughing and get up off on the floor. Of course the electronics guy was several shades of red...[This message was edited by David L. Donald on 26 June 2004 at 02:18 PM.] |
Eric West
Member From: Portland, Oregon, USA
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posted 26 June 2004 02:45 PM
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I ALWAYS put a three to two ground removing adapter on my Peaveys. Before I did it I used to pop capacitors in my Session 500. Afterward, for some reason I never popped another. I realized that probably half the clubs I played in had the ground wire attached to the neutral side of the plug to begin with, and god knows what else. If you know anything about electric panels, go in and check some of the clubs' boxes. Especially check the neutral bar to see how many bare ground wires are attached to it. You'll be surprised. They'll scare you to death if know what you're looking at.. My wiring at home, and in my music room was done by me IAW the 1996 NEC and duly inspected by the OR State Electrical Inspector, and it passed. My "MOS" in the USAF was 54250, Interior Electrician. My grounds are run to an isolated bus, tied to my cold water inlet, and two 6 foot copper clad ground rods. Modern insulated equipment like the Podxt, (and most all hand tools) are isolated and have none. I run with sharp objects, and have been known to throw garbage out of airplanes with my name on it. EJL
[This message was edited by Eric West on 26 June 2004 at 07:22 PM.]
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Lee Baucum
Member From: McAllen, Texas (Extreme South) - The Final Frontier
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posted 27 June 2004 10:56 AM
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quote:
and have been known to throw garbage out of airplanes with my name on it.
Eric. Was your name on the garbage or on the airplanes? (Subtle English grammar humor.) 
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Lee, from South Texas
Down On The Rio Grande |
Eric West
Member From: Portland, Oregon, USA
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posted 27 June 2004 11:03 AM
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No, it's a fair question..It was on the garbage. "English is a language that was designed by crooks to take things from people without them understanding how it happened." -Eric West-
 EJL |
Ray Minich
Member From: Limestone, New York, USA
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posted 27 June 2004 05:34 PM
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quote:
If you know anything about electric panels, go in and check some of the clubs' boxes.
You only wanna do that AFTER a few toddies, not before, else it could scare ya ta death...[This message was edited by Ray Minich on 27 June 2004 at 05:34 PM.] |
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