# PA noise from monitors seems to be from lighting



## 94VG30DE (Nov 28, 2007)

OK guys, I know this is a long post but I want to explain the whole situation so it's easier to diagnose. 

I have a problem that I can't seem to figure out, so I'm soliciting new ideas. The setup is that the church I help run PA in just got 4 new small Nady powered monitors. They seem to be nice units, and have enough output across the 4 to overpower the room and still stay pretty clean. We got them up and running last night, and there was buzzing coming out of all of them. We also noticed that the buzzing seemed to go away when we turned off the two front rows (closest to the platform) of recessed lighting. I believe all of those bulbs are incandescent. 

The FOH board only has two monitor sends (1/4" stereo), so we are running the 4 monitors off Y-cables at the board. We pulled the Y's out and ran the monitors straight, and that helped just a little, but was definitely not the main source of our noise. We will be getting shielded splitters to fix this issue. 

But the main noise is still there. When you pull the 1/4" plug out of the back of the monitor the noise disappears, so it doesn't seem like the monitor is the problem. We double checked the entire run of the snake and re-soldered every connection. The run is actually all XLR, but the 4 channels for the monitors are terminated as Speakon connectors into a plate at the platform and 1/4" stereo at the board. The cables on the platform are Speakon to connect to the plate on the floor and then 1/4" on the other end into the monitor. 

Anybody have any ideas? The whole run of cable is grounded as far as we can tell (we've tested everywhere we can think) and we tried plugging the monitors into a power conditioner and it didn't help. I can't figure out how to test if bad wiring in the recessed lighting is causing this because it's 50 feet in the air... 

Thanks for any help or ideas for further testing. The singers will be grateful.


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## 94VG30DE (Nov 28, 2007)

Would this work? 
Parts Express:Ferrite Core 1/2" Cord Noise Suppressor 
It doesn't make sense to me to wrap the power cord of the monitor into it if the noise already dies when I pull the _signal_ cable out.


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## funkymark (Apr 5, 2009)




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## fredridge (Jan 17, 2007)

are these monitors powered or passive? 

if they are powered and you are running 1/4" into then I think you are losing the benefit of the xlr run and should be having some type of impedance transformer rather than just terminating them with 1/4 or speakon

When they did out church there was something special about the power on stage. it was grounded differently.... the plugs were orange to signify this.

Nady is not known for the highest quality equipment, so could be that too...... try plugging the monitors in near the sound room and see if the noise is still there, if it isn't you are picking it up on the long run of cable


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## 94VG30DE (Nov 28, 2007)

fredridge said:


> are these monitors powered or passive?
> 
> if they are powered and you are running 1/4" into then I think you are losing the benefit of the xlr run and should be having some type of impedance transformer rather than just terminating them with 1/4 or speakon
> 
> ...


The monitors are active. I realize we are wasting the benefit of the XLR run, but we were trying to not have transformers on every line as that would get expensive really quick, especially compared to what we paid for the monitors. 

As I mentioned, the board we have is rather limited, so I only have the two 1/4" jacks for monitor sends. 

I wasn't happy about the Nady choice either, but like I said apparently we got them for a good price. We did already test them by plugging them in right in the sound room, and had no noise there. It sounds like it is picking up the noise over the run. 

I am starting suspect the quality of the wiring, considering we had to re-solder some of the XLR connections because they had wires switched. We are going to look into the wiring of the light-switches and breaker box this week to make sure all of those are properly run, and also pull the platform up again (it's a false-floor for all the cabling to run under) and see where the snake runs with respect to how the platform power is run. I have a feeling it's a mess, and is going to be a fun web to untangle. 

When you say your power on the stage was grounded differently, can you elaborate on exactly how they did that? Our floor is going to be apart anyway, so this is the time to fix stuff. I already know the power is nasty/dirty and some of it isn't perfectly grounded, but I'm not sure what to do from here to fix it.


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## Riveted1 (Oct 23, 2008)

Before you start ripping stuff apart.....

If you disconnect the 1/4" cables, does the noise go away? If so, you have a ground loop between where the monitors plug in and your mixing console. If not, then leave the 1/4" cables disconnected and turn off the lights you suspect may be causing the problem. Does it go away now? Keep trying different things until it (hopefully) goes away. Most of the time, it will just be a ground loop.


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## 94VG30DE (Nov 28, 2007)

Riveted1 said:


> Before you start ripping stuff apart.....
> 
> If you disconnect the 1/4" cables, does the noise go away? If so, you have a ground loop between where the monitors plug in and your mixing console. If not, then leave the 1/4" cables disconnected and turn off the lights you suspect may be causing the problem. Does it go away now? Keep trying different things until it (hopefully) goes away. Most of the time, it will just be a ground loop.


When I disconnect the 1/4" cable at either end (either from the console or from the monitor) the noise goes away, even with lights on. Most of the time when I shut the two suspect lights off (with the cables plugged in), the noise goes away. It is some interaction between the signal wires and the power wires. The more I read and think about it, the more I think I have a ground loop isolation problem. I think there are audio components going to the common (main) ground, or worse, there is no ground loop separation at all. That would explain the high noise floor for any monitor I plug in on the platform.


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## Riveted1 (Oct 23, 2008)

Yep, you have a ground loop. Since you are obviously limited in your power choices, I would find a way to get the monitors plugged in to the same circuit as the console, ie. run some extension cords, although this may not be feasible in a church.

Another way to do it is to put a ground lift on one end. I would not suggest using one of the little AC ground lifts as this might cause other problems. You want the ground lift on the 1/4" cables. There are many boxes on the market that can achieve this. Cheap man's version would be a pair of DI boxes w/ground lifts.


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## chad (Jun 30, 2005)

There is noise on ground from the dimming system, is it a standard wall dimmer or are they on dimmer packs in a dimer rack? You may have a dimmer going if it's only ONE dimmer feed that does it.

As opposed to reading EVERYTHING I'll ask. The 1/4" output, is it balanced on a TRS connector? Do the monitors have the provision to jump from one to another instead of using a bunch of Y cables? Are you indeed running balanced? if so are you sure? and if you are sure, lift the ground (pin 1) on the XLR connector at the speaker end of the send, ALSO make sure that just pin one is connected and NOT THE SHELL OF THE CONNECTOR. if the shell is tied to pin one isolate that before lifting pin one. A true balanced rig will run well with pin 1 lifted and in theory it should be.


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## Riveted1 (Oct 23, 2008)

chad said:


> There is noise on ground from the dimming system, is it a standard wall dimmer or are they on dimmer packs in a dimer rack? You may have a dimmer going if it's only ONE dimmer feed that does it.
> 
> As opposed to reading EVERYTHING I'll ask. The 1/4" output, is it balanced on a TRS connector? Do the monitors have the provision to jump from one to another instead of using a bunch of Y cables? Are you indeed running balanced? if so are you sure? and if you are sure, lift the ground (pin 1) on the XLR connector at the speaker end of the send, ALSO make sure that just pin one is connected and NOT THE SHELL OF THE CONNECTOR. if the shell is tied to pin one isolate that before lifting pin one. * A true balanced rig will run well with pin 1 lifted and in theory it should be.*


Which was my point earlier about the DI's. Since 'most' engineers have a couple laying around, he could try the in-out thing and lift the grounds to see if that was his problem. Easier than cutting the grounds and realizing that's not the problem and having to re-solder them. 
And I agree w/the pin 1 lifting in a balanced system.


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## chad (Jun 30, 2005)

DI boxes are not 1:1 there will be either a wicked level shift or distortion. They make 1:1 iso boxes, but they are not cheap, easiest way is to whip one up out of scrap parts.

I carry several XLRM-->XLRF with pin 1 lifted as troubleshooting devices. There is no sense in introducing a transformer if it's not needed. I have transformer iso on my amp rack coming from drive but it can be disengaged, that was a damn expensive project but has saved my ass in more than one "oh ****" moment.


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## 94VG30DE (Nov 28, 2007)

chad said:


> There is noise on ground from the dimming system, is it a standard wall dimmer or are they on dimmer packs in a dimer rack? You may have a dimmer going if it's only ONE dimmer feed that does it.
> 
> As opposed to reading EVERYTHING I'll ask. The 1/4" output, is it balanced on a TRS connector? Do the monitors have the provision to jump from one to another instead of using a bunch of Y cables? Are you indeed running balanced? if so are you sure? and if you are sure, lift the ground (pin 1) on the XLR connector at the speaker end of the send, ALSO make sure that just pin one is connected and NOT THE SHELL OF THE CONNECTOR. if the shell is tied to pin one isolate that before lifting pin one. A true balanced rig will run well with pin 1 lifted and in theory it should be.


The light switches are not dimmers at all, they are simply on/off. Thats why I was a little taken aback b/c I have no had this kind of problem with a normal grounded lightswitch before. 

The 1/4" monitor sends are UNBALANCED from the board. The monitors do have the capability to daisy-chain, but that only really helps me on 1 pair. I have a pair of monitors at the pulpit which are Send A (just for the main speaker/singer) and then one on the far left and far right sides of the platform (maybe 40 feet apart) for Send B. 

If I were to run one extension cord back from the mixing desk, that still should be kept >0.5m from the snake run, correct?


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## guitarsail (Oct 12, 2007)

I was just about to say you could always try a 1:1 Iso box like the whirlwind 1x3 Splitter or such but they are EXPENSIVE.. but chad's covered all the items I was going to recommend...lifting ground on a unbalanced line isn't going to help or be a good idea...so thats out...

I wouldn't worry about it being any distance from the snake..You're not going to be sending enough power or what not down the extension cord to be a problem...if you were running a Socapex or 3Phase power or some such thing I would say keep it away but just an extension cord isn't going to introduce noise on the snake at all.....

Out of curiosity what console are you using???

Since after reading more before posting it was isolated down to some power issues somewhere. I would at this point after reading  double check the re-soldering job on the snake that was done, as your going to do, clean up the rats nest of cables you inevitably have, and report back. Since you already checked the monitors at FOH you know signal is picking it up somewhere...just need to iso where its happening..

HAPPY HUNTING!


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## 94VG30DE (Nov 28, 2007)

Console is a Yamaha EMX3500-16. 
I will try running an extension cord up to the platform to power the monitors. 

I will also try running both Send A monitors off the one signal to hopefully reduce noise that way. 

I will report back when I have more testing done. In the mean time, feel free to keep firing ideas/suggestions at me if you feel so led.  Thanks for all the help guys.


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## guitarsail (Oct 12, 2007)

Where is the split to the monitors being made? Cuz if its on the original than it'll be on the daisy chained as well so it wont make a difference...


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## 94VG30DE (Nov 28, 2007)

guitarsail said:


> Where is the split to the monitors being made? Cuz if its on the original than it'll be on the daisy chained as well so it wont make a difference...


Split to the monitors is being made right off the mixing console. Nevertheless, point taken.


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## Riveted1 (Oct 23, 2008)

I think this topic is being over-thought just a bit. This is not a touring rig, it's a house rig running unbalanced connections. Pin 1 lifts are great for balanced connections. And iso boxes would be great if he has the $ or time, which seeing as he's running unbalanced lines, I doubt the $ is there, and if he's like most of us, the time isn't either. 

In a pinch, I've used CHEAP DI's as I've described and it worked fine as a temporary solution.  Might get him through a service or two until he can come up w/a permanent solution. Although with running unbalanced and balanced equipment together, hum is just the nature of the beast w/out true isolation.

But, if he can run an extension cord to the booth, it should solve his problems w/out any need for anything else. But who knows.... grounds are a funny thing!


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## chad (Jun 30, 2005)

Once again, DI's ARE NOT 1:1, THEY ARE FAR FROM IT.

He's running an unbalanced line too far in too noisy of a place. the lights... they aren't halogen with a transformer in them are they?

Touring or not, do it right or look like a fuggin idiot, some "church soundguys" get a bad rap and cost the congregation money when a REAL soundguy or consultant has to come in and fix their mistakes. Remember it's largely volunteer, they come and go, do it right the first time.


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## guitarsail (Oct 12, 2007)

DI's are not the fix, like chad said. DI takes a line level through a transoformer (not iso 1:1) and drops it down...a bunch..


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## Riveted1 (Oct 23, 2008)

Like I said, it's not a permanent fix, and I realize there is work that needs to be done. But it might get him through in a pinch, like if he needed the monitors on Sunday. 
I agree w/everything you guys have said, and there is no replacement for doing it right the first time. I've walked into plenty of situations where the PA was "rigged"- it's not fun. 

Ground Loops/Isolation


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## guitarsail (Oct 12, 2007)

Well its not a matter of permanent or non permanent fix. If you use a "normal" DI like for instruments and put it in life it will knock the signal down so far as to be almost unusable, as apposed to an ISO 1:1 which will keep it at the same level. IF he needed the monitors on Sunday and dropped a intrument DI in line...they would now be minus the noise, and music because there would be hardly any level.


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## 94VG30DE (Nov 28, 2007)

Haha thanks guys, good conversation. I don't have any (even cheap) DI boxes on hand, so I have this week to find a fix. We are running the monitors right now, we just have the volumes lower than we want them, and there is a lot of noise. 
The point is that even to get cheap DI boxes (that sound like they might do little/nothing) I am going to have to spend money, so if I'm spending money it needs to be on a _solution_ not a bandaid. You are correct though, the money is not there, and the time is short too. Luckily I have been pushing for a full monitor setup since Christmas, which means that some of the tax-return money was set aside for this project. I'm sure we have a little bit of money left, but not enough for a fancy solution. Extension cords and wiring we can do


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## guitarsail (Oct 12, 2007)

Extension cords and wiring will fix it


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## 94VG30DE (Nov 28, 2007)

guitarsail said:


> Extension cords and wiring will fix it


Let's hope so. I'm working on it tomorrow night, so I will post back with what I find.


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## 94VG30DE (Nov 28, 2007)

The problem is fixed (I think)... 

We pulled up the platform, and the outlet that was supplying power to the front two monitors is ~8" from where the snake comes out, so we have reason to believe they are run together for the whole run. This can't be fixed because BOTH are run in the concrete. We ran an extension cord from the mixing desk anyway, all the way up to the platform to power the monitors, and had same noise. During this I had my DMM looking at the continutity between the ground in the outlet next to the snake and the shield pin on the back of the Speakon connectors in the plate. The first part of the waveform is with no lights on, the second part is with one light on, and the third part is with two lights on. The graph goes from fine to messy, and when it is messy is when we get audible noise. 

We turned off breakers til we found the one that powers the mixing desk, and it turns out that it also runs the outlet next to the snake. This means that power-wise, the monitors and desk are all on the same circuit. We opening the breaker panel, and there are two breakers labeled "audio." One of them powers the mixing desk and some of the front outlets. We did not figure out what the other one powers. All grounds in the breaker panel were grounded to the same buss bars, which hooked up to a copper wire feed that was bigger in diameter than my thumb. 

We tried the ferrite cores around the audio cables going to the monitors, and all the power cables in the area. The PA guy said Wednesday when he put them on it decreased the noise, but taking them off on Friday didn't seem to make a difference to my ears. 

On a whim, I took an ungrounded extension cord I had, popped off the blocker that keeps me from putting the grounded 3-prong cable from the monitors in backwards, and put the monitor power cable in ungrounded. All my noise went away. I could now crank the volume up full, and had almost 0 perceptible noise. So we went around and popped the grounding plug off all the monitor power supply cables (they are just standard cables so we can get more non-rigged ones if necessary) and hooked everything back up like it was originally (using the power supply that runs right next to the snake). 

No noise out of the monitors no matter what we play through them. *Did I do a bad thing by no longer grounding the powered monitors?* They have an active anti-feedback thing that they do, and that does not seem to be effected during our limited testing. Should I be keeping a closer eye on the temperature of the monitors now? They have a big finned passive cooling plate on the back. 

Pictures below show all the stuff I just talked about.


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## chad (Jun 30, 2005)

You disrupted the safety ground, it's unacceptable by professional standards, you need transformer isolation. the problem was a ground loop.


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## 94VG30DE (Nov 28, 2007)

Yeah, that's what I figured. So what specifically am I risking/damaging by running the setup that way? When we found that that "fix" would kill the noise, the PA guy immediately went around ripping off ground prongs. I felt really uncomfortable watching him do that, but I couldn't specifically say what we were risking. If I can provide a decent case for what we are potentially damaging, I can probably get them to spend the money to actually FIX the problem rather than making other problems for ourselves down the road. Thanks again for all the expertise guys


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## chad (Jun 30, 2005)

94VG30DE said:


> When we found that that "fix" would kill the noise, the PA guy immediately went around ripping off ground prongs.


Tomorrow, punch him in the face, hard, and tell him that it was from Big Dady.



94VG30DE said:


> I felt really uncomfortable watching him do that, *but I couldn't specifically say what we were risking*. If I can provide a decent case for what we are potentially damaging, I can probably get them to spend the money to actually FIX the problem rather than making other problems for ourselves down the road. Thanks again for all the expertise guys


you are risking killing people, nuff said.

I have stories, some great ones.  I have seen the strings of a bass make a SM58 grille look like someone took a bite out of it... I have seen scorched lips (experienced them once) I have see ambulances... you don't want that ****.

It takes ONE person to bring in an amplifier to play that is mis-wired before a church service can turn to a funeral service


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## 94VG30DE (Nov 28, 2007)

ouch, ok that's what I was worried about. I will swap the chords in the morning, and deal with the noise at the expense of only worrying about the resurrection of one person... 

Where do I get these "1:1 isolation transformers" from? I did a quick search and found a lot of theory, but some of them are $30 and some are $60 and some are $250, and I have no idea what is going to get the job done...


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## chad (Jun 30, 2005)

I would personally put all the safety grounds back in place EXCEPT the powered monitors for the time being, then order isolation, I'll look for something for you, do you want off the shelf or do you want to home-brew? ANYTHING that ANYBODY touches on a regular basis needs to be grounded, like mixers (mics) instruments, etc.


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## guitarsail (Oct 12, 2007)

Un-grounded amps= BAD...just like chad said...to many time i've seen people just lift ground with those stupid 3pin edison to 2 pin minus ground and facepalmed. Its just dangerous practice when there are other ways to fix things..Personally if its missing the ground on any cables of mine I cut em off so people stop using them and then go fix them. 

Im at the girls house so not time for a further reply


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## 94VG30DE (Nov 28, 2007)

The powered monitors were the only things we ungrounded. Two of them are physically sitting on the ground, and two of them are on pedestals next to the pulpit. None of them should be touched as the singers aren't allowed to touch anything, but I realize that it is still a safety factor. 

Off the shelf would be nice, but if it can be done home brew, and the components are just as easy to get ahold of (and significantly cheaper), that's no skin off my back. I don't know how to do much of this, but I am pretty good at following a wiring diagram and solder.


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## fredridge (Jan 17, 2007)

scary stuff...just be careful....I try and be cautious about this stuff big time...especially after reading about the pastor who electrocuted himself by touching a mic during a baptism.

I remember seeing a kid at church lean his guitar up against the wall, it started to fall over and one of the strings got caught on a plug, big spark, burned the outlet and scared the heck out of everyone. Fortunately it wasn't any worse.


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## chad (Jun 30, 2005)

fredridge said:


> scary stuff...just be careful....I try and be cautious about this stuff big time...especially after reading about the pastor who electrocuted himself by touching a mic during a baptism.


In a baptismal "tub" situation, wired is plain stupid, a shotgun mic is the choice. Ground is NOT ground unless bonded, and that ground between the service safety ground (bonded to the mic) and the ground derived by the rusty cast iron drain pipe coming out of the OTHER side of the OLD part of the church could have vastly different potentials...... and even at a lower voltages, with water surface area all over you... current kills, voltage does not. The volts jolt, it's the mills that kill.


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## chad (Jun 30, 2005)

we may have a winner!

http://www.diymobileaudio.com/forum/diy-mobile-audio/57776-amps-balanced-input.html#post712818

posts 14,15,16


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