Lifting Grounds

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I have noticed a lot of guys talking about,"lifting grounds", to prevent ground loops. I might mention that this is a very dangerous practice, especially with equipment powered with 120 volt house current. Most of the time, the case of equipment is grounded. If you remove the ground, then you could "BECOME" the ground by touching the case. The last thing you want to do is "BECOME" the ground, when dealing with 120 volt house current.

------------------

Jack Stoner · From: Kansas City, MO

I agree that lifting grounds can be a potential hazard. If it has to be done, to get around ground loop problems, the best way is not to lift the ground on the unit that the guitar is directly connected to but to some other unit.

The ideal thing would be to have an industry standard that all equipment manufacturers adhered to and then there wouldn't be a problem (but that will never happen). Some units have separate signal and power grounds, some have common signal and power grounds, some do not have an AC power ground (e.g. devices with a wall wart), some have AC, DC and signal grounds, etc.

Proper design of input circuitry will also help to minimize hum problems.

Using my Transtube Fex with either a Nashville 400 or a Session 400 LTD (or both) into the power amp input jack on the back of the amps, I had to lift the ground on the amps (even if only one amp was used) to eliminate the ground hum problem!

C Dixon · From: Duluth, GA USA

Probably the two most important posts ever to be written on the Steel Guitar Forum.

Folks, I gotta tell you, when you are messing with "grounds" on power line powered devices, you better be careful.

And a piece of advice to anyone, being private or company---NEVER say in print to remove a ground on any piece of equipment. You risk a damage suit bubba!

This is serious stuff.

I realize the annoying and frustrating problems we face with hum, noise etc from "ground loops". But we are talking about human life here.

Caution!

Walk with Jesus,

carl

CrowBear Schmitt · From: Ariege, - PairO'knees, - France

Being an electrician, i confirm: Don't disconnect Ground on your equipment !!!
preferably do as Mr Jack Stoner says:
Disconnect elsewhere on another unit.
Not the amps, or the PA / record equip.
How 'bout the Coke machine ? uh oh ;;;

Rich Paton · From: Santa Maria, CA.,

Keith, there is the subject of "lifting" signal grounds, vs. AC safety grounds.
You can find info under "system interconnections","considerations in grounding & sheilding", as well as a ton of other no-nonsense data, at the RANE tech. library:
http://www.rane.com/library.htm#rnotes

Robert Parent · From: Gillette, WY

I agree with Carl on this one!

Find and fix the problem do not cut the safety ground connection under any condition.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Rich, how do you come up with these great sites? Loads of great information on this site. Thanks!

------------------

Rich Paton · From: Santa Maria, CA.,

Keith...The answer is: too much time spent on the internet!
As far as the Rane website is concerned, I have used their excellent equipment since buying a PE-15 Parametric EQ six years ago.
Their "Tech Library" is truly a treasure of "No-B.S." info on pro audio subjects.

basilh · From: United Kingdom

Hi Lads ?,
I think that the answers about "Lifting Grounds" might also mention the fact that the component drawing the MOST current has the LEAST resistive path to earth (ground) and therefore should be considered as the MAIN ground for the whole system.(This is almost certainly the power amp) The rest of the accessories CAN and should have the ground lifted to prevent hum caused by loops.The ground is carried from one unit to the other by the shield.It's only occasionally that a rack unit has a jack socket and circuit board that's "Floating" with respect to earth.

Here in Ireland we don't have a TRUE mains earth, the ESB (Electricity Supply Board) send us power with a system called neutralized earth. The ground is common with the neutral.
Baz

BTW. I have spare leads made up for my gear and mark the ground lifted ones with RED pvc tape near the mains plug, that way if I come across a venue where I get interference, I can easily swop around the leads, and usually cure the problem.

Rich Paton · From: Santa Maria, CA.,

It is common and often necessary to operate test equipment such as ocilloscopes, rms voltmeters, signal generators, etc. with the ground "lifted" by using a 3 prong to 2 prong "adapter" on the instrument's power cord.
However, those employing such methods are generally well trained, have experienced nasty shocks and become trained, or have been electrocuted.
The purpose of the "U-Ground"(USA)pin is to "return" a power-to-chassis fault (short circuit) from a chassis and/or cable shield to the distribution panel, in order to trip the circuit's breaker or blow the fuse when fuses are used. If due to faulty wiring, abrasion of insulation, or a power transformer short such a defect exists, the lack of the ground "return" would allow the "hot" power lead to place a hazardous voltage on the chassis and any connected input signal cable shield, guitar strings, etc. you would definitely have a potentially lethal situation.
However, I think the reference to "lifted grounds" in the context presented here pertains to the preamp, signal processor, or power amp input sheilds being "lifted" from the chassis of the piece of gear to eliminate "ground loops" and resultant hum.
I have several power amps, rack mounted mixers, parametric Eq's, etc. which all incorporate switches to allow this mode of operation.
They have nothing whatsoever to do with the proper connection of the AC safety ground, which should always be connected. Typical club and bar venues' stage wiring, in my experience, is far too haphazard and dangerous to even consider such schemes as lifting the equipments' power cord safety grounds.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I agree that the signal ground can be different than the power ground on some musical equipment. You can have a dual polarity power supply ,with a common, which some call the ground. This common, or ground, with dual polarity power supplies, in most cases, is different than the main power supply ground. The common, or ground, may ,or may not, be earth ground. This all can get confusing for musicians not trained in electronics. When a untrained person hears of others lifiting grounds, they think of getting rid of the main power grounds. This "COULD" possibly make the metal enclosure on a instrument effect case ,or amplifier not have a ground. If you touch this ungrounded metal case, under the right conditions, electricity flows through you, and you become the ground. The electricity don't care if you are the common, the floating ground, the ground, or earth ground. Electricity takes the path of least resistance.
I am aware of big transformers with "FLOATING" grounds or commons. They are not just in Europe, we have them in this country. I recently was called to correct a industrial electrical problem at a new newspaper. The newspaper had burned up $26,000.00 worth of computers. People were getting shocked from time to time. The service came in with three 480 transformers, and was broken down into various smaller 3 phase breaker boxes. We checked one 208 volt 3-phase box. We touched neutral to case ,and the fire shot. We had over 100 volts from the neutral to the case. We figured out the problem. The electrician who wired the new building ,and the transformers, failed to connect the neutrals to the grounds in the main 480 volt incoming transformers. Therefore, if there was any kind of failure in the newspaper electrical complex, there was no return path to earth ground. I don't care what country you are in, electricity works the same way.
I am aware in many countries power is supplied in different ways. I stand on my original statement which was this, "Removing a power ground, thus lifting a power ground, is dangerous business."

------------------

Rich Paton · From: Santa Maria, CA.,

Keith, I had a service call as an electrical contractor, on a 50HP agricultural irrigation pump installation. As I turned off the main road down a dirt path toward the well, I turned on my "Tick Tracer" to test the battery. as I got within 100 feet of the well, all hell broke loose on the tracer, like I had never experienced in 25 years.
The walnut orchard foreman had pressed the "Start" button on the motor starter can, as he had done hundreds of times, except this time he was greeted with a thunderous expolosion that he was somehow lucky to survive unscathed . The sides of the steel control enclosure were blown outward, and severe carbon tracking was everywhere inside, and all the connecting screws on the starter and control relays had their heads melted off(!).
Further investigation indicated that the utility had a subcontractor replace the old three phase delta connected transformer bank with a new pole and 45KVA, 12,000V primary to 480 unit, with wye connected secondary. Fine, except (and I had NEVER seen THIS sin committed), forgot to ground the neutral connection on the transformer.
The old control was a total loss, and the difficult and expensive to replace pump motor (2 technicians @ $75.00 each/hr., 6 hours labor)was smoked.
The line-to-ground phase voltages at the service disconnect lugs were:
A:940VAC, B:725VAC, C:490VAC, rather than the proper 277 or so volts.
The monetary cost to the customer was about $3,800.
I immediately hired a professional photographer, to document the damage and ungrounded transformer installation, and submitted about 40 full color, 8"x10" glossy prints along with a 15 page detailed report.
The utility still had the audacity to deny the claim (later paid in full, after mediation by the state utilities commision). All this was simply due to an extremely ignorant installer(s), and the lack of $30 worth of grounding conductor and a $10 grounding rod & clamp. It was VERY fortunate no one was burned, filled with shrapnel, and/or killed.

Lee Baucum · From: McAllen, Texas (Extreme South) The Final Frontier

Splain something for me. What is the function of the "Ground" switch on the front of my Nashville 400? It is a 3-way switch.

Lee, from South Texas

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Great question Lee! Reading from the Peavey Owners Manual for the Nashville 400, I quote:"POLARITY SWITCH--This switch is a three position type with the center, zero position, completely removing the internal grouinding capacitor from the circuit. This position is normally recommended for situations where the AC power receptacle is known to contain a properly grounded third wire. If properly grounded AC main supply is not available, a suitable ground adaptor should be used. The (plus and minus) positions are used to ground the amplifier properly when only two wire services are available. One of these positions will yield the lowest amount of residual hum or popping when the instrument is touched. NOTE: Polarity Switch is not operative on export models."

------------------

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Please ....let me add to keith's post above.

"This switch will do NOTHING to decrease the possible shock damage to a person.... It's ONLY function is to reduce the hum level caused by improber grounging (i.e. like in an older house,or any TWO wire ac supply.)

Do NOT believe that this switch will protect you from harm !! I have seen more than one person serverily hurt by grabbing a "LIVE" mike while holding a Electric guitar. ( I do NOT mean to slam ANY brand of Electric insturments here as 99.99% of them are correctly wired.) It's just a matter of fact that "When we use electric power to enhance the sound, we must treat the electrical part of this just as carefully as we would treat a weapon/gun."

"Been There,, Done That"

Mark Amundson · From: Cambridge, MN USA

Let me attack the problem from the reason why some are forced to lift grounds; hum. If the first grounded AC powered circuit (usually the guitar amp or rack preamp)had the intact ground, then suceeding grounded circuits like second guitar amps or additional power amps would cause the ground loop hum. If all input jacks where TRS (Tip-Ring-Sleeve)instead of TS, then manufacturers could have BALANCED inputs and outputs instead of using the shield to complete the audio circuit (and ground loop).

Most pro-audio stuff made today is TRS or XLR balanced, so maybe some clever manufacturers could start using balanced circuitry. It is fully backwards compatible since TS plugs short the ring connections and are still usable.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Mark, I agree with you ,as usual. The problem is really basic. How many guitars and amps do you think Peavey ,or Fender would sell in "MUSIC-LAND", if they had XLR jacks on them? How many pedals would I sell with XLR fittings? "ALL"-Guitars and amps have 1/4 inch jacks. So, putting balanced XLR jacks on something would make the product "ODD MAN OUT!" The industry has accepted this when it comes to P.A., and broadcast equipment. It will take some brave moves by a manufacturer to convert guitar players to hook a XLR balanced line jack into their guitar. I don't know if Peavey or Fender is big enough to make that happen. Even if it did happen, there would be those who thought they got a better sound with 1/4 jacks and shielded lines, instead of balanced lines. Just like there are people who like the old tubes instead of solid state. I suppose there are those who never embraced the automobile, and are still riding horses. Although, that number is more than likely getting smaller day by day!

------------------

rickw · From: nc

I knew a man in the 70's his amp made loud hum -the string melted on the steel-no eq. groud-a penny behind the fuse-his body was clear of steel-yes the dance had a fire.

Forum Index > Electronics		Next oldest topic :: Next newest topic