Getting Rid of Ground Loop Hum

[Sheryl McDonald]

What's the best way to plug up electrical equipment to get rid of ground loop hum? <Paul Kotapish mentioned in another thread about a configuration to eliminate it and didn't elaborate. Rather than hijack that thread, I thought I'd start a new one.>

When our celtic band plays, I usually bring the Behringer powered mixer, (vocals, acoustic pickup for mandolin and fiddle) and our guitarist plugs her guitar into her small crate amp [she likes the sound better]. Often I'll hear that "lovely" hum in our system.

We normally just plug into the house electricity, and don't bring anything special to buffer it (power conditioners, etc). I'm trying to travel as light as possible.

Suggestions on this?

[pops1]

Does the Crate have a two prong plug or a grounded plug? If it is a two prong plug turn it around 180 degrees and plug it back in. Also the Crate may have a ground switch in the back if so flip it.

[Chunky But Funky]

If the above posts recommendations fail to produce the results you're after, (it should), maybe try one of these:

EB Tech Hum X

Doug

[foldedpath]

A filter like that Hum-X is a good thing to have in your PA's tool kit. However, I think of something like that as a last-ditch emergency tool, after you've gone through your rig and made sure everything is hooked up properly. If you're not familiar with what causes ground loop hum, and methods to deal with it, check out this this article on audio interconnections from the Rane web site.

Try the methods listed in order, starting with always trying to plug all your AC-powered gear into the same outlet circuit. This shouldn't be difficult with a small PA and a band using mostly acoustic instruments. Then move down the list if that isn't fixing the problem, until you get to things like lifting the ground at destination end of audio cables (not the ground on a power cable!) as shown in the Rane article.

If you're still getting hum, then you could try a filter like the Hum-X. But if you've solved other problems with how you're hooking up your gear, you might not need it. Start with the basics, first.

[mandomedic]

One of the cheapest and most effective ground hum eliminators I have ever found and use is a ground plug adapter... You can buy these at any hardware store... They're usually gray and have on the female side, two blade and a ground hole and on the outlet or male side, just the two blades. Many, Many times I have used this simple device and lifted the ground to eliminate hum... Simple is good! Kenc

[mclaugh]

The power ground connection is there for safety. Lifting it is dangerous. It is worth the time and effort to follow foldedpath's advice and go through your system and fix it right.

[Paul Kotapish]

Rane has a fairly extensive discussion about the problem and potential solutions here:

http://www.rane.com/note110.html

The page includes numerous diagrams for setup, wiring, etc.

It's worth a look.

[TonyP]

All the above are excellent. One other consideration is see if there are any lights on dimmers that are on the same circuit that you are powering your system off of. When full on, they don't make any noise, but when you dim(like some do for simple lighting) they cause a nasty hum.

I use a Furman which is really just a glorified rack mount power strip, but it helps to keep everything on the same circuit, and have not had any hum yet, except when like the above mentioned happens. Then if I can't get away from it, just turn the lights all the way up and go with it.

[SternART]

What Mandomedic said above has worked for me. A simple 2 prong adapter.....it is worth a try!

[foldedpath]

All the above are excellent. One other consideration is see if there are any lights on dimmers that are on the same circuit that you are powering your system off of. When full on, they don't make any noise, but when you dim(like some do for simple lighting) they cause a nasty hum.

Yeah, I forgot about that one. Another problem is neon signs in bars, which can set up an RF field that causes havoc in passive magnetic pickups, and in some types of digital effects gear if it's not well-shielded. RF interference is different from ground loop hum, so it's just something else to be on the lookout for.

I use a Furman which is really just a glorified rack mount power strip, but it helps to keep everything on the same circuit, and have not had any hum yet, except when like the above mentioned happens. Then if I can't get away from it, just turn the lights all the way up and go with it.

I use a Furman rackmount power strip too, just one of the basic models. It does help enforce the "plug into just one outlet" rule for small PA's.

Another problem is when you get into older buildings where the outlets look like they're 3-prong grounded, but they're not, for one reason or another... usually someone trying to duck a permit inspection. Not much you can do there, except make sure the singer is told not to touch their lips to the microphone.

[pops1]

The ground and the neutral are the same thing and go to the same exact place in the fuse box. The ground lift adapter will work fine and safely as you still have to plug the cord in with the ground, hot and neutral all in the right places. It becomes dangerous if you break off the ground lug and then can plug it in wrong giving you a hot chassis. Something easy is the best and this is easy. Keep it safe and keep it original.

[JeffD]

One of the cheapest and most effective ground hum eliminators I have ever found and use is a ground plug adapter... You can buy these at any hardware store... They're usually gray and have on the female side, two blade and a ground hole and on the outlet or male side, just the two blades. Many, Many times I have used this simple device and lifted the ground to eliminate hum... Simple is good! Kenc

Very dangerous! Please folks, don't ever do this.



Some of the adapter plugs come with a wire on the male side with a lug end that you connect to the screw in the center that holds the plate on. Other adapters come with a little spade lug on the male side, for making the same connection. The idea is to make a two pronged outlet into a three pronged outlet. When used properly, the adapter does not lift the ground, but provids for its connection.

If you use the plug incorrectly, as most people do, by failing to make the ground connection, you are creating a potentially dangerous situation.


Your equipment will probably work, and you may get rid of your hum, but you have disabled a safety feature of your power system.

Like driving without seat belts, you may get away with it, but its not a good idea.

I repeat, please don't ever do this.

[Chris Keth]

I haven't heard anybody mention the best option, if the problem isn't the building: fix the grounding of your equipment!

[mandroid]

stuff like shielding in the pickup cavity , perhaps,..

I love neon beer signs , i can make the hum louder if I hold my pickup closer , but not make it go away.

[have not used the piezo or the Schertler in that bar, just the magnetic one.. ]

[Mandophyte]

The ground and the neutral are the same thing and go to the same exact place in the fuse box.

This may be true at dc, but at audio and radio frequencies it is not.

The neutral and earth cables may actually be connected together at some point, but the impedance differences between the two cables can cause considerable problems.

In the UK the connection is at the electricity supply substation or transformer and there may be several volts between earth and neutral. People have been known to run door bells from this supply.

The reference to using a single socket is very wise. At a pub I used to frequent a band didn't have enough sockets so they put an extension cable through the window to the floor above, --- resulting in a loud and expensive bang. Electrical phases are 415V apart!

The introduction of PMR (protective multiple earthing) in the UK has caused all sorts of problems for audio and radio amateur (hams) fans alike. This is because the earth wiring is no longer returned to a single connection at the fuse box, but may consist of a collection of loops.

Ideally all your equipment should be connected to the same earth point, not via various sockets.

Be safe out there!

[pops1]

Here both the neutral and earth ground attach together in the fusebox and then go to a ground rod. There can't be a difference unless it is an induced voltage from something in the air and that will be induced to any unshielded wire even then it should be bled to ground and the induced voltage would only be between the hot and neutral which already has 120 volts ac and could carry an audio frequency on top of it. Some P.A. systems have a ground lift to stop hum from ground loops.

If you can build an extension cord with 4 or however many outlets you need and plug everyone into one outlet. If you still have hum, it's in your equipment or the building. Don't assume that the building is wired right, i have seen several times that it is not.

[EdHanrahan]

Just for some perspective...

When I was playing Beatles and Beach Boys stuff back in college (yes, the '60s!), there WERE NO GROUNDED OUTLETS or 3-prong plugs. Between several Fender, Ampeg, and I think Bogner (PA) amps, something was probably humming. Worse yet were the shocks from the mike to your lips!

We just got a bunch of alligator clips and 8-foot pieces of hook-up wire and ALWAYS grounded the amp chassis together. We're still alive!

[JeffD]

Here both the neutral and earth ground attach together in the fusebox and then go to a ground rod. There can't be a difference unless .....

Unless your adapter, as peviously describe, has isolated you from that ground, and the chasis of your equipment becomes hot due to some equipment malfunction, errant or loose wire, or spilled beverage.


We want to avoid any life changing experiences.

[mandroid]

had ungrounded outlets in an apartment I rented, so to ground the outlets. a foot long drill was bought , and a length of wire , and a clamp around the sink to attach it to the cold water pipe .

there are testers that you can plug into the outlet to tell you the ground is working right , or not.

[KanMando]

First things first. Is the outlet you're plugging into grounded, and is it wired correctly? Maybe not. I found this to be the case in my own house. My amp hummed like crazy when I used it in the den, but not in other areas of the house. Turns out the neutral and the hot connections were reversed in the outlet. To make matters worse, the outdoor receptacle on the patio was also wired incorrectly. This is especially dangerous. A cheap and easy way to check your outlet integrity is with an outlet tester like the one in the attached photo. This one is $5.99.

Bob

[pops1]

Best place to start. KanMando good call. I carry a test light that i can check for hot chassis or bad outlets.

[Martin]

Using a two prong adapter to lift the ground is fine to use as long as there is a common ground for all the equipment. Folks that tell you never to do it have obviously never had to set up equipment at a dfferent venue every night.

[mandroid]

A worthy consideration,

A Power Conditioner [more than a surge protector , filters and levels out under and over-voltage too ]

I have a whole armada of gear in my apartment run thru one..
helped on storm induced power outages and such when spikes happen,

there are smaller, lunch-box sized, ones that you would plug in 1st, the power strip into that . like:
http://www.parts-express.com/pe/show...number=248-777

http://www.parts-express.com/pe/show...number=125-102
and rack-mount ones too ..

[mandomedic]

Martin, you are exactly correct. I have worked in electronics since I was 10 in my uncles repair shop, held a FCC license for many years, and know my way around both AC and DC.. I still stay the simplest and easiest way to eliminate it is to use the ground adapter. Kenc

[Chris Keth]

An interesting aside:

I remember seeing in some documentary where David Gilmour was telling someone about their method of checking if the mic or strings were hot when Pink Floyd played all over in the 70s and 80s. He said when you're all plugged in you put your hands behind your back and touch the mic stand with the strings of the instrument. He also mentioned that one time in the 70s Roger Waters (PF's bassist) did that and it arced and popped two of his strings. That's some current to burn through a couple of electric bass strings!