eliminating power hum in old buildings?

[Vito Corleone]

I know this is a fairly common issue, but what is the best and/or easiest way to eliminate/reduce the problem?

 

Last night we were playing in an older building (c. 1955) and were faced with horrible noise/hum through the guitar amps. (Both single-coil pickup Fenders, BTW). Usually the light dimmers are the problem in these buildings, but even turning the house lights off didn't reduce the buzz. Pulling out the Les Pauls with humbuckers MIGHT have solved the problem, but neither guitar player brought those to this gig. The PA, bass and keyboard rigs were quiet.

 

But as a general solution, is there some sort of device that can be used that solves the (grounding?) problem in these older venues? Do they make filters that the band can use on our end? Or is this something that is pretty much unavoidable?

[piersonm]

High quality power conditioner always works for me. 4-5 stage is what you want. Buy a 100pos unit and expect no change.

[agedhorse]

Generally, power "conditioners" are worthless in these instances. Especially if the noise is being induced into the pickups. Power filters can not correct a ground that does not exist. Also, those power conditioners that you mention are more effective (assuming there is a ground) at RF frequencies, not a 120Hz and 60Hz hum/buzz. The filter components would be enormous and heavy.

 

Frankly, repairing the wiring is the proper and safe solution... assuming that is the problem.

[Vito Corleone]

 

Frankly, repairing the wiring is the proper and safe solution... assuming that is the problem.

 

 

Well, even if I had the skill level, repairing the wiring in somebody else's building isn't something I could probably finish between soundcheck and the first set.

 

But I take what you're saying to mean that, should we get booked at any gigs in these old crummy buildings in the future that we pretty much just have to deal with the noise?

[dennis a]

If the problem is NOT a ground loop and you think it is coming from fluorescent fixtures or dimmers, an EMI filter MIGHT correct the problem.

[agedhorse]

 

Well, even if I had the skill level, repairing the wiring in somebody else's building isn't something I could probably finish between soundcheck and the first set. But I take what you're saying to mean that, should we get booked at any gigs in these old crummy buildings in the future that we pretty much just have to deal with the noise?

 

 

I'm suggesting that they fix their wiring so that next time you don't have the same problems.

 

In fact, you may have to deal with the noise, or if it's induced into the pickup systems, you might have better luck with the humbuckers.

[Unalaska]

Always take an outlet tester and use it! Find 1 or 2 good circuts and only use those 1 or 2 outlets only. Start there.

[The Chinese]

I've had luck in the past by carrying a Ebtech Balanced power Rack. Probably not the greatest thing in the world, but it will quiet down those pesky Guitars. The caveat is that I've heard (never actually experienced this) that some Guitar amps of the Vintage variety won't work.

 

Todd A.

[Vito Corleone]

 

I'm suggesting that they fix their wiring so that next time you don't have the same problems.

 

 

In a perfect world, yes. Unfortunately, what I'm dealing with is doing casuals in venues where the band that shows up to play is the venues last priority. This last gig, for example, was a wedding we played in a beautiful country club built in the 1950s. I'm sure the wiring was updated at SOME point to some degree (they DID have 3-prong outlets at least!) but obviously not very well. The venue was doing 3 weddings that day of which we were playing one. After getting a guestimate from the house "tech" that this-wall and that-wall were on two separate 15-amp circuits, I found we had a horrible noise from the guitar amps. When I asked the house 'tech' for suggestions he told me that "most bands that come here have the same problem" and walked away to deal with some other issue in another room.

 

Odds are we'll never play that venue again. But the odds are that we WILL play a similar venue with similar crappy wiring in the future.

 

In fact, you may have to deal with the noise, or if it's induced into the pickup systems, you might have better luck with the humbuckers.

 

 

Yes. I'll suggest we drag along the Les Pauls next time we're headed into the great unknown, just in case, and hope that helps. I was just hoping there was some sort of filter, transformer, conditioner, or other workaround that existed for such situations that I wasn't familiar with.

[agedhorse]

In a perfect world, yes. Unfortunately, what I'm dealing with is doing casuals in venues where the band that shows up to play is the venues last priority. This last gig, for example, was a wedding we played in a beautiful country club built in the 1950s. I'm sure the wiring was updated at SOME point to some degree (they DID have 3-prong outlets at least!) but obviously not very well. The venue was doing 3 weddings that day of which we were playing one. After getting a guestimate from the house "tech" that this-wall and that-wall were on two separate 15-amp circuits, I found we had a horrible noise from the guitar amps. When I asked the house 'tech' for suggestions he told me that "most bands that come here have the same problem" and walked away to deal with some other issue in another room. Odds are we'll never play that venue again. But the odds are that we WILL play a similar venue with similar crappy wiring in the future. Yes. I'll suggest we drag along the Les Pauls next time we're headed into the great unknown, just in case, and hope that helps. I was just hoping there was some sort of filter, transformer, conditioner, or other workaround that existed for such situations that I wasn't familiar with.

 

Unless you know the exact cause, it's not likely that a magic solution is going to work. That's unfortunately the nature of these kinds of problems. Too bad they don't see to just getting a potentially dangerous problem fixed. I guess wedding decorations rate higher on the list

[Vinny D]

Sometimes even cheap Furman power conditioners get lucky and eliminate some noise but most of the time what really needs to be done will come at the owner of the venues expense.

The best way to get rid of the problem is they need an isolation transformer installed with a seperate panel to power just the stage and PA system.

Good luck getting a venue owner to cough up the bucks to do that:wave:

[agedhorse]

 

Sometimes even cheap Furman power conditioners get lucky and eliminate some noise but most of the time what really needs to be done will come at the owner of the venues expense. The best way to get rid of the problem is they need an isolation transformer installed with a seperate panel to power just the stage and PA system. Good luck getting a venue owner to cough up the bucks to do that:wave:

 

 

Why an isolation transformer when we do not know whatthe actual cause is?

 

An isolation transformer is justified for very, very specific conditions, where a ground must be derived and then referenced to something that may not be as common to the building system bond point as would be desireable, or for applications where high frequency noise is coupling across the transformer core, and an electrostatic shield/ground is indicated to reduce this coupling capacitance.

 

We don't even know if it has to do with the electrical system itself. It could be, for example, discharge lighting or cold cathode lighting radiating noise that's being picked up be the single coil pickups. An isolation transformer will do nothing for this. It could also be a missing ground wire, just a grounded receptacle scabbed in.

 

In 25 years of designing electrical systems for (large) venues, I have had to use an isolation transformer only once in my career. Isolated ground systems are standard, but not isolation transformers. Totally different things.

 

To the O.P., does the volume of the noise decrease when the volume of the amp is turned down? How about when you unplug your cable from your amp at the amp end? Noise change or eliminated?

[Vito Corleone]

 

To the O.P., does the volume of the noise decrease when the volume of the amp is turned down? How about when you unplug your cable from your amp at the amp end? Noise change or eliminated?

 

 

In this case, yes. In fact, the noise went away when the guitar volumes were turned down at any point, so it was pretty clearly a noise being picked up by the single-coil pickups.

 

Of course, a couple of weeks ago in another venue, the issue was a noise that was in ALL the equipment at ALL volumes that went away once the house lights were turned off. I'm guessing there are probably as many different problems and solutions for these problems as there are venues?

 

Would there be any advantage to using one of these things? Not that we always have access to a 220 outlet, but sometimes we do.

 

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200326702_200326702

[agedhorse]

Completely dependant on the venue and what the real problem is. Different solutions for different problems.

 

Portable power distro depends on the power source being properly wired of course. Yes, it often reduces problems based on poor branch wiring.

[Craig Vecchione]

guido61, note that Agedhorse had two questions. What happens when you unplug guitars at the amp end of the cable?

[Vito Corleone]

 

guido61, note that Agedhorse had two questions. What happens when you unplug guitars at the amp end of the cable?

 

 

That killed the noise too. Like I said, reducing the guitar volume at any point in the chain--guitar volume pot, floor pedal, disconnect guitar from cable, cable from amp, turn down amp volume---all got rid of the noise. Moving around changed the volume of the noise too. It was clearly something the single-coil pickups were picking up.

 

This isn't a specific problem I run into often. In fact, never had it this bad before. I know it has to do with the crummy wiring in these old buildings and not our gear per se. But the more we play these sort of venues, the more often I run into SOME sort of power/noise problem of one sort or another.

 

I guess I was hoping for some sort of one-size-fits-all solution I could throw into a rack or a box that hasn't been invented yet.

[dennis a]

 

Would there be any advantage to using one of these things? Not that we always have access to a 220 outlet, but sometimes we do. http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200326702_200326702

 

 

GFI circuits can be a pain in the butt for sound systems requiring more than one circuit...specifically circuits powering from separate hot legs. They want to trip prematurely.

 

Dennis

[rhat]

sometimes flipping over the plug can get rid of noise. or if you have a switch on the back of the amp can reverse the polarity .

[agedhorse]

 

I know it has to do with the crummy wiring in these old buildings and not our gear per se.

 

 

No, you do not know if it has ANYTHING to do with the wiring. In fact, it likely does not. It could be completely independant, like radiated noise from a beer sign's neon tube, defective flourescent fixture, dimmer and wiring with no risetime limiting, etc.

 

This is the point I am trying to make... unless you know exactly what the problem is, ANY proposed solution is like pissing into the wind.

[The Chinese]

 

sometimes flipping over the plug can get rid of noise. or if you have a switch on the back of the amp can reverse the polarity .

 

 

 

Which would require breaking the ground lug. Very BAD idea.

[Vinny D]

 

No, you do not know if it has ANYTHING to do with the wiring. In fact, it likely does not. It could be completely independant, like radiated noise from a beer sign's neon tube, defective flourescent fixture, dimmer and wiring with no risetime limiting, etc. .

 

 

 

This is why an isolation transformer with a dedicated panel for stage use only works well.

You will not get the noise from signs, ballasts, dimmers, etc.

[agedhorse]

 

This is why an isolation transformer with a dedicated panel for stage use only works well. You will not get the noise from signs, ballasts, dimmers, etc.

 

 

Bullcrapola. If the noise is not entering the amplfier through the power source (the OP's problem is definately not power related) then there's absolutely no benefit to using an isolation transformer. The noise is being radiated from the devices (neon tubes, fl tubes, ballasts, even transformers) and coupled magnetically as well as electrostaticly into the pickup and instrument's grounding system. Strings are an excellent receiver of such noise and the electric field can be coupled quite easily into pickups as well as the ground wiring of the instrument. Shielding is not perfect.

 

In fact, the promotion of isolation transformers for stage power (for almost all applications) borders on irresponsible in that those specifiers (and the companies that sell them) often make claims that are just patently false.

 

The only performance benefit of an isolation transformer is where the propogation of electrical noise (that is high frequency harmonics) is of sufficient magnitude to couple into the audio portion of the equipment powered by the AC line. This is really very uncommon, in order to meet international RFI/EMI standards, (quality) devices are designed and constructed to minimize or reject the effects of such signal on the power lines (called conducted radiation, received, in the tests). In order to pass these agency tests, the designs are generally quite robust regarding the passage of conducted radiation across the transformer. The tests we design to are typically ~2.5kV, and represent conducted EMI pulses.

 

The other benefit is where a 440/480 volt primary is the site power supply, and a local unit transformer must be used to get 120/208V. At that point, a derived ground is created and the neutral must be bonded to the ground. Since everything else is already there, adding a couple hundered dollars for an isolation barrier is trivial.

 

Myth Buster: An isolation transformer will not do anything for reducing ground loops. That is an isolated ground system, one that uses seperate grounding paths independant of the building's conduit and steel system, bonded back to the system's bond point (ideally, though benefits can be seen bonding back to the source's distribution or subpanel too).

 

I have designed the power system for maybe 100 theatres, churches and venues. Only once have I used an isolation transformer. I generally, though not always, use an isolated grounding scheme and I NEVER have noise problems when I design the electrical and audio systems. Never.

[Keyrick]

Andy is completely correct. As the noise varies with movement of the single coil instrument, the likely culprit is a neon Beer Sign or florescent lighting. You can have the best grounded system in the world, but if you are near a poorly designed Neon beer sign or a bad ballast in a flourescent light fixture, some single coil pickups will pick up hum.

 

Rick

[Coaster]

this may border on OT, but how do you deal with the older dimmer pacs that create noise that comes through crummy shure wireless mics? i only have the issue with the low end stuff, PGX or some such. i also get this noise with some active bass guitars, kind of a metallic swoosh sound when the scenes change or a buzz when the scene is static and the lites are not 100%. these are older NSI dimmers

[agedhorse]

 

this may border on OT, but how do you deal with the older dimmer pacs that create noise that comes through crummy shure wireless mics? i only have the issue with the low end stuff, PGX or some such. i also get this noise with some active bass guitars, kind of a metallic swoosh sound when the scenes change or a buzz when the scene is static and the lites are not 100%. these are older NSI dimmers

 

 

It depends on how the noise is getting into the audio. Generally, it's because of the fast risetime of the voltage (dV/dT) due to the switching nature of the SCR's (or triac) in the reverse phase control mechanism.

 

The way the industry addresses this is by using an inductor in series with the load that limits the current risetime due to instantaneous change of voltage. Higher risetime chokes are larger, heavier and more expensive. Any question why the less expensive dimmers use lower risetime chokes?

 

There are other ways the noise gets propagated, that's with line and load wiring that's not in (grounded) metallic conduit, higher than desireable source impedances of the supply, shared phase or neutral conductors with the audio supply (along with high impedances), load wiring running very close to audiio wiring, etc. It's also possible that it's corrupting the FM link too, though not quite as likely.

 

It's complicated, and troubleshooting may take some specialized tools. First determine tha path of interference, then why it's happening, then you can propose some solutions.