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Discussion Starter · #1 ·
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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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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Discussion Starter · #5 ·
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
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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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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Discussion Starter · #7 ·
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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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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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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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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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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Discussion Starter · #12 ·
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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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 :D 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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Discussion Starter · #14 ·
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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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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Discussion Starter · #16 ·
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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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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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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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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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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