Noise on Audio System

J

JimS888

Member
Location
California
Occupation
Electrical Contractor
I have a problem that I've spent months trying to diagnose. Our church recently moved to another building and installed a new audio system. The problem is that there is noise coming out of the audio system. It sounds to me like A/C hum. I seems to be related to the electric guitar and bass. When the system is powered up, the sanctuary lights are on and the guitar is plugged in with the gain turned up, there is an irritating buzz/noise/hum coming out of the speakers.

The setup is a multi amplifier rack powering speakers and subwoofers. There is LED and fluorescent house and stage lighting powered through a large Leviton dimmer rack. The dimmer is powered from an underground line that comes from a distribution panel (Panel "S") with a 230 amp 3 phase breaker. Panel S is fed from the main service located in a metal cabinet outside the building. That main service is fed from a transformer owned by the electrical utility.

The noise is at its worst when the lights in the sanctuary are at full brightness. When I shut the lights off, the noise is gone. The noise increases as the electrical load increases. When the guitar player faces forward or he turns 180 degrees, facing backward, the noise is somewhat reduced but when he turns to either side the noise gets worse.

Tests I've tried:
Bypass the dimmer panel by wiring the lights directly into the feed coming from Panel "S" - No improvement in the problem
Tried Furman power conditioners on each phase in line with the lights. - No improvement in the problem
Installed a Furman Power conditioner in the line feeding one of the amps. - No improvement in the problem
Temporarily disconnecting the ground going to the guitar foot controls. - No improvement in the problem
Tried a dual pickup guitar (Humbucker) - Slight improvement in the problem
Temporarily fed the dimmer panel from an isolation transformer that feeds another panel. - No improvement in the problem
I've tried several other tests with no success and am stymied, so I am reaching out to this forum for help
I talked with the installers who put in the new audio equipment and they seem very knowledgeable and professional. Several of them quickly said the problem isn't a ground loop but didn't explain their reasoning but it seemed to be based on the fluctuation in the noise when the guitar player turns from side to side. They offered no other explanation.
The in house audio tech bought a small device that plugs into an outlet that buzzes and displays line noise and the readings correlate with the noise coming out of the audio system.

I also set up a small portable 110 volt generator outside and wired several of the light channels into it, bypassing the dimmer rack. - the noise was gone! This test was just a small number of the lights but those same lights alone running through building power makes noise.
I also plugged one of the Furman power conditioners into a nearby 120 volt outlet and ran those same lights and that also seemed to cure the problem.

So I think I've eliminated the dimmer rack as a source of the noise and there also seems to be similar noise in other parts of the building when plugging a guitar into a small amp. My current theory is that the problem is emanating from somewhere upstream of Panel "S".

Has anyone ever run into anything like this? Any things you can suggest to test?
 
You may have a single fluorescent ballast or LED driver spewing RF. Bring in a portable radio with an AM tuner, tune to an empty spot in the AM band. There will be a nasty buzz blanketing most of the band if a ballast or driver has become a radiator. Try to use the radio to find the offending fixture (the buzz gets louder the closer you are), otherwise you'll have to remove bulbs/unwire drivers one-by-one to find the baddie.
 
Two papers by Audio Engineering Society noise and interference experts:

An Overview of Audio System Grounding and Interfacing
by Bill Whitlock, retired President Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers

Power and Grounding for Audio and Video Systems
A White Paper for the Real World – International Version
Jim Brown Audio Systems Group, Inc.
 
JimS888 said:
When the guitar player faces forward or he turns 180 degrees, facing backward, the noise is somewhat reduced but when he turns to either side the noise gets worse. Tried a dual pickup guitar (Humbucker) - Slight improvement in the problem ... [They] didn't explain their reasoning but it seemed to be based on the fluctuation in the noise when the guitar player turns from side to side.
Click to expand...

Based on this and the fact that there is no noise until there are guitars connected indicates that your problem is EM interference that is being picked up by the guitar pickups. Looks like it may also be carried by the building wiring.
JimS888 said:
The noise is at its worst when the lights in the sanctuary are at full brightness. When I shut the lights off, the noise is gone.
Click to expand...
So, you have pretty much narrowed down the source. Now think what is it about those fixtures that is causing the problem. LEDs are known for this.

-Hal
 
Any guitar or just some guitars?
If it's just some guitars, you can use them as a tester.
Lost Neutral current flowing thru a water pipe or a single wire, can create a field that may be picked up by old guitars.
 
I don't think it's a fluorescent ballast since only one circuit is fluorescent and all the rest are LED. It makes noise when any of the lights are on.

All electric guitars we've tested make noise, single coil pickups are worse than double coil. Acoustic guitars don't make noise since they don't have pickups so my theory is the noise is being picked up by the pickups as RF?

I don't know who Designed or installed the system in 2005. The building is new to us since last fall. It's difficult to inspect the LED fixtures since they are 50+ feet over a sloped floor with permanently mounted seats. I can connect and disconnect them but I don't know what else I can do. Maybe an RF reading device?

Thanks for the two papers. I will read them.
 
I was thinking about connecting several space heaters to test with a resistive load to see if the noise occurs based on load vs load from the lights.
 
JimS888 said:
I don't think it's a fluorescent ballast since only one circuit is fluorescent and all the rest are LED. It makes noise when any of the lights are on.

All electric guitars we've tested make noise, single coil pickups are worse than double coil. Acoustic guitars don't make noise since they don't have pickups so my theory is the noise is being picked up by the pickups as RF?

I don't know who Designed or installed the system in 2005. The building is new to us since last fall. It's difficult to inspect the LED fixtures since they are 50+ feet over a sloped floor with permanently mounted seats. I can connect and disconnect them but I don't know what else I can do. Maybe an RF reading device?

Thanks for the two papers. I will read them.
Click to expand...
Are the guitars plugged into a direct box?
 
JimS888 said:
All electric guitars we've tested make noise, single coil pickups are worse than double coil. Acoustic guitars don't make noise since they don't have pickups so my theory is the noise is being picked up by the pickups as RF?
Click to expand...
No. Looks like electromagnetic. I don't know if this is even still a thing, but some churches provided assisted listening for people that were hearing impaired. It was a simple system called an inductive loop; a loop of single conductor wire was run around the perimeter of the room where worshipers sat. The ends were connected to an audio amp which was provided with the same program material as the speakers. Hearing aids at that time (and maybe still) were required to have an inductive pickup coil- like a guitar. That was mainly to enable it to work with a telephone handset and allow the person to hear through their hearing aid, but it also worked the same in a church that had an inductive loop.

Since you "inherited" this building, sound system and electrical system there is no telling what the previous owner did.

JimS888 said:
I was thinking about connecting several space heaters to test with a resistive load to see if the noise occurs based on load vs load from the lights.
Click to expand...
Can't hurt. I'm trying to think of what you can rig up for an inductive pickup connected to small amp with headphones. Then walk around with that.

-Hal
 
JimS888 said:
Temporarily fed the dimmer panel from an isolation transformer that feeds another panel. - No improvement in the problem
Click to expand...
Decades ago I did a job to fix noise in a studio designed by a EE that worked in a large studio in Nashville. He had us install a isolation transformer that was 240: 60/120V secondary for all audio gear. Its a special system the 120V secondary is Line - Line so it has to be GFCI protected as covered in article 647. Its a bullet proof system and gets rid of the noise every time. There are cheaper off the shelf rack mount units that do the same thing.
 
Balanced power. But I don't think the noise is coming in on the power since it's only there when guitars are in use.

BUT

JimS888 said:
I also set up a small portable 110 volt generator outside and wired several of the light channels into it, bypassing the dimmer rack. - the noise was gone!
Click to expand...
It would be interesting to see what would happen if you powered the audio system from a generator.

-Hal
 
How close is the dimmer rack to the guitars? Perhaps the noise is radiating from the dimmers themselves. A million years ago, the SCR dimmer controls in our high school auditorium radiated crap that was picked up by the WE52 operator headsets used by the follow-spot operators. You could hear the crap's waveform change shape as the dimmers were faded up and down. It didn't help that the headsets were wired with zip cord instead of twisted-pair, but I didn't install it. :)
 
The dimmer rack is in a room that is about 10' to 15' behind and about 20' above the guitar player. We've moved the guitar all the way to the back of the sanctuary with little or no improvement. Also, I bypassed the dimmer rack completely with no improvement.
 
A little more details on the settup would help.. are you using a seperate amplier for the guitars and bass? A microphone? Direct line out of amps? Direct into the mixer? What do you mean "more gain" makes hum worse?! Gain on the board? Amp? Tried db cut? Eq out the hum?
Most guitars will hum when hands arent touching the strings...
Have you tried a volume or fader instead of gain?
Try a noise gate...
 
Thanks for your reply. Keep in mind I'm an electrician, not an audio engineer. It's a professional setup with 4 separate amps plus one for subwoofers. There are usually 2 guitars, a bass, drum kit, keyboard and a couple microphones. Only the electric guitars and bass produce the problem and it increases or decreases based on which way the guitar is rotated. They have tried a noise gate, I think. More gain might be the wrong term but he turns it up at the mixer and also at the boxes on the floor where the guitar is plugged into.
 
The first and perhaps most important (sort of) question is- dedicated actual guitar amps? as appossed to the p.a. power amps...
Id pass it off to the sound guy otherwise.. besides, there is no heavenly virtue to rock and roll anyways... :)
 
If I read correctly it sounds like it is only guitars exhibiting the hum and These are connected via cables?
On the assumption the "noise/hum" is induced via that path you could try to isolate the cabling from the guitar itself using a wireless guitar transmitter. I would expect the cabling to make a better antenna than the pickup alone. Try eliminating all cabling & effects pedals etc. using the wireless receiver located directly at the amplifier as a temporary/diagnosis tool.
 
Hook a dummy source resistance equal to the guitar pick-ups to the ends of the cables.

I'll take a SWAG at a value and suggest 1000-1500 ohms, a half watt resistor soldered to a 1/4" jack.

THAT will tell you yes or no whether it is getting in at the guitars' pick-ups or if its the cabling (or something else)
 
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