Powered Monitor Electrical Hum

What is the source at the console and what input are you running into on the Hot Spot? Where are the gain settings on the console and the monitor? The Hot Spot inputs will accept a wide range of signals, from mic to line to instruments, and the PA5X140 supposedly senses whether it is a mic or line signal and automatically adjusts for that. However, it may still simply be a gain structure issue. Have you tried varying the level at the console and does that affect the noise at the speakers or let you turn down the speaker's input level? Do you have another powered speaker that you coudl use to see if it has exhibits the same problems?
According to the product data, the 1/4" input on the PA5X140 is balanced. There is also 24VDC phantom power on the XLR.

Brad might have found the problem IF the XLR CONNECTION has 24 volts Phantom power, and you are feeding this back into a line out on a mixer you are bound to have problems, plus phantom power uses the ground connection.

Possibly you need to get a trs to female XLR adaptor and connect your xlr cable to the trs jack for input
Sharyn
 
we are having the issues on both of our powered monitors (same model #, serial# is one digit diff). also we are having the same issues whether running it on 1/4 input or XLR input. unfortunately when i did the test for the 1/4 input it was only TS because we lack the proper adapters. i can look into a price tag for it though. i would love it if i could manage to get a hold of a male TRS to Male XLR cable in tucson, *hint hint* anyone in tucson, az able to help out. i can try removing pin one from it anjd see if that helps however that is going to require me to actually use tools :D.
 
Here's a ridiculous idea, call the dealer the church bought them from.
Or any dealer for that matter, they might know if there any defective lots floating around.

I know some people in Tucson, but they will charge you.

For technical support, service or repair call 1-800-369-7768 or email Aaron at [email protected]
 
Better yet -- send them to me! I'll try them out on Smokey Joe's, which we're doing in December, and I'll let you know if they worked okay ;)

Seriously, if there is a problem with these monitors that they don't handle the grounding well, I'd like to know. I was considering picking up a couple of them myself.
However it doesn't seem likely that the monitors would be defective ... I'd think we would have heard about this type of problem before if they were.

Otherwise, the first rule of thumb when troubleshooting -- isolate the problem ... find out when it works, and when it doesn't. I can't tell from the above threads that you have been able to find out when it works. I assume you tried the obvious of using different cords and plugging into different outputs from the mixer (group out, channel direct out, aux out, utility out, etc). Does it work when connected anywhere on your board? If not, I would try to find a different board and/or find another venue nearby where you can bring the speakers and try them out with their equipment.
 
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try to find a different board and/or find another venue nearby where you can bring the speakers and try them out with their equipment.
Heck, go to your local music store with them.
Notice I say local(as in mom and pop) the Banjo Center frowns on this type of thing.
Probably better ask the pastor before you go taking stuff out of the building though.
 
Ok guys i think i moved past my own stupidity. i verified and double checked that it was plugged into the same outlet as the board and the hum disappeared. crap i hate it when i do stupid things. oh well. ok. i just did a ton of tests with this new knowledge. http://stoney.djfaithmusic.com/tests_run.xls
also all these tests where done using Group out 3 on our A&H GL2200 32ch.
 
AHH yes the faulty ground connection. I have had endless arguments with electricians on this, the ones used to home office shop wiring simply don't understand. It is very common in churches etc where in many cases where the volunteer does the work and it is not done properly.

What happens is a variety of the following

Sometimes some one replaces the outlet, and gets the hot and neutral connection reversed, or the neutral and ground connection reversed. The cheap 3 light tester will find the first problem but NOT the second.

Code allows for the use of metal conduit for the ground connection, and to save money, the contractor will not pull a green ground wire thru to all the outlets. Works fine for lights, but for audio is a mess, over time the conduit connections corrode, weaken get disconnected, or sometimes wind up touching something that could be a ground say for instance the conduit runs in such a way that it is strapped to something else, and that for instance is a water pipe, or the conduit from another circut, now you have multiple paths to ground, and you get a potention difference, and a hum

Sometimes a sub panel is installed, and the person gets the neutral bar grounded to the box, now you have again two ground connections.


For hum free audio, you either need
To plug everything into the same outlet, (if the interconnection of ground on the same circuit is bad you will get hum even if it is on the same circuit. Obviously this many times is not practicle but in some places I have had to run an extension cord all the way from the stage back to the mixer at FOH just so everything was on the came outlet.
Isolation transformers on the line that interconnect also work, and fix the problems also.

Bring a distro, have it hooked into the main panel and then YOUR wiring is what goes from the distro to your units.

Get an electrician to fix the ground, I recommend if at all possible, changingn to ground isolated outlets, and then having a complete ground wire pulled. This is not cheap, and sometimes it is easier to have them simply run a new set of circuits for you on stage and FOH and have the new connections all have a complete isolated ground only connected to the service ground at the main panel.

Another thing to keep in mind that a lot of people miss is that surge protector strips that have gone bad, will work but have ground problems. This is why in general for amps for instance people tend to just have a quad box, no Surge protector, and a voltage regulator/ups for the FOH equipment, and then have isolation transformers on the line feeds.

Sharyn
 
so basically there is nothing i can do other than running a 200 ft electric cord back to the booth? or get the electrician to rewire it? out of our entire booth we use two outlets and two power strips. our equipment on those power strips is wireless equipment and our music playing equipment.
 
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ok I did another test and I think I have finally narrowed it down far enough. the test i did was almost exactly like the first one i did in my attached xls sheet previously except i did it on stage instead of in the booth
XLR to 1/4 stereo with and without gnd lift on AC showed a result of a hum without the lift and works prefectly with. I'm thinking that the problem is actually two problems, first it is a ground issue overall (though the precise problem with ground eludes me) plus a issue in the circuitry of the amp in determining if it needs the phantom power or not on the XLR.
what do y'all think?
 
I'm thinking that the problem is actually two problems, first it is a ground issue overall (though the precise problem with ground eludes me)
You might have the neutral and ground bonded at a subpanel. They should only be bonded at the service entrance.
plus a issue in the circuitry of the amp in determining if it needs the phantom power or not on the XLR.
what do y'all think?
There is no such thing, amps don't supply or use phantom power.
 
Sounds like you've narrowed it down to one problem, the pin 1 connection between your board and amp. I join in avkid's confusion about why phantom would be present on the output, and if it was a multimeter between pin 2 (or 3) and 1 on the output in question will read (approx.) +48V DC and then you will have identified a second (and unlikely) problem which wouldn't be audible even if it did exist.

If simply lifting the ground removes the problem then a simple ground lift at the board should answer your problem. You seem reluctant to get hands on with your wiring, and for less than $10 in materials you could build your own ground lift and practice the art of solder. Great chance to find a multimeter and get a feel for how to quickly check whether the power in a room is going to give you any trouble.

And to explain what I believe your ground issue to be: The voltage on the signal and return ( pin 2 & 3) has to be in reference to another voltage, Ideally this is zero and is ground. When voltage makes its way onto ground the difference between the signal and the reference (ground) changes, this change is audible. Since AC changes is polarity in 60Hz cycles, when this power gets onto the ground we hear it as a 60Hz tone. How voltage gets onto the ground is often the less obvious answer as there are many ways to do this.
 
There is no such thing, amps don't supply or use phantom power.[/QUOTE]

Allow me to correct my speech, previously it was stated that the circuitry in the monitor can detect a mic line in that require phantom power.

Wouldnt it be a safety hazard to do a gnd lift on the board? I am a little bit hesistant to start doing wiring for a few reasons, first because i have never done it, second, because i lack the tools, third, because ppl in leadership above me want me to make as few changes as possible, fourth, because I lack proper space to work on it.
Plus where would i find instructions on how to build a ground lift for $10

And to explain what I believe your ground issue to be: The voltage on the signal and return ( pin 2 & 3) has to be in reference to another voltage, Ideally this is zero and is ground. When voltage makes its way onto ground the difference between the signal and the reference (ground) changes, this change is audible. Since AC changes is polarity in 60Hz cycles, when this power gets onto the ground we hear it as a 60Hz tone. How voltage gets onto the ground is often the less obvious answer as there are many ways to do this.[/QUOTE]

How would i verify what the main AC or subpanel AC ground is, like verify if it has been done properly.
 
I did a little digging and the engineers specs for your box state that the XLR connection carries +24V DC. I'll have to get back to you on how this might affect a boards output circuitry. If you suspect it might be the cause of some of your grief then a simple female XLR to TRS would let you avoid the problem. Sorry if I was unclear about what I meant by ground lift. I didn't mean to lift the ground off the boards AC; this would be unsafe and floating the boards chassis could affect your whole system negatively. I was reffering to a fem to male XLR adapter with the shield disconnected inserted between the board and amp; this is the $10 ground lift. Less than $3 for each connector (cause of course your gonna buy neutrix) and 6" of mic cable. simply solder pin 2 to pin 2 and pin 3 to pin 3, and trim back the exposed shield and don't connect it. This is all a grnd lift is.

How much experience do you have with soldering and using a multimeter?
 
There may be some confusion. The monitor in question is intended to have a microphone connected directly to the XLR input. The internal electronics has circuitry that automatically detects whether the input signal is mic or line and apparently does provide phantom power on the XLR.

When you really get down to it, grounding problems are actually in the audio electronics and not in the grounding, this is the Pin 1 problem that has become a common topic. Properly designed audio equipment should work with any code compliant power grounding without a problem, the signal ground should be grounded at the connections and not pass through the active electronics signal path within audio devices. There is an AES Standard, AES48-2005, "AES standard on interconnections - Grounding and EMC practices - Shields of connectors in audio equipment containing active circuitry" addressing this and many newer pro audio products are designed to be "pin 1 compliant". However, many products are not and most older products do not incorporate the AES48 information, thus the need to continue to address the problems via the grounding system.

I believe that the ground lift being suggested is the signal ground and not the power (safety) ground. Lifting the safety ground is indeed dangerous as well as being a code violation, and the practice should be limited to being used as a momentary diagnostic tool, if at all.

I personally think that a high quality input transformer such as one from Jensen or Lundahl on the line feeding the monitor and located at the monitor might be a good solution.
 
I would question this speaker's abilty to detect if it is a mic or a line feed and then decide to provide phantom power, It is possible, but not very likely. I would quess that it uses the trs connection for line, and the xlr for mic level.

You have several choices

One is make up a cable that can lift the audio ground, I would suggest that this be an xlr to trs cable, since I am guessing that the speaker really expects line level in on the trs connection

you could get a isolation transformer, this will break the feed of Phantom power and eliminate the problems also, without seeing how you have the mixer and levels set it it POSSIBLE that you are feeding a very low level signal from the board to the amp and again this could be confusing this supposed circuit that can detect mic vs line ( most properly designed system would have just added a swtich to turn off phantom power.

BUT BASED ON YOUR TEST I THINK IT IS A DIFFERENT PROBLEM

The fact that running them all on the same electrical outlet eliminated the hum does point to the system having a pin one problem. Basically this is when the connection for the audio signal shield pin one, is connected to the ac ground on the equipment. This is an incorrect design, but is common. Here again, simply make cable that on the end at the speaker/amp has the audio shield pin one lifted.

Long term if you don't want to drive your self crazy, you need to get the ac ground fixed. Standard electrician is not likely to be able to do it, will argue that there is a continuous ground, but is not likely to be able to detect that there are multiple ground connections in the circut.

Sharyn
 
I did a little digging and the engineers specs for your box state that the XLR connection carries +24V DC. I'll have to get back to you on how this might affect a boards output circuitry. If you suspect it might be the cause of some of your grief then a simple female XLR to TRS would let you avoid the problem. Sorry if I was unclear about what I meant by ground lift. I didn't mean to lift the ground off the boards AC; this would be unsafe and floating the boards chassis could affect your whole system negatively. I was reffering to a fem to male XLR adapter with the shield disconnected inserted between the board and amp; this is the $10 ground lift. Less than $3 for each connector (cause of course your gonna buy neutrix) and 6" of mic cable. simply solder pin 2 to pin 2 and pin 3 to pin 3, and trim back the exposed shield and don't connect it. This is all a grnd lift is.
How much experience do you have with soldering and using a multimeter?

how much experience does none qualify as? i know the concepts of it, but like most of things in life knowledge doesnt count as much as experience. I did a test with a female XLR to TRS on stage and it still had a hum until i put a AC gnd lift. now i might be able to drag up some connectors and do the 6" patch cable without shelling out money. :D i will see what i can do next time i am there. unfortunately i usually get your responses right after i leave. :( i will talk to ppl and see what i drudge up.
 
You gotta start somewhere, sooner's better than later. If you do have a ground issue then the TRS connector won't change anything, but i agree with the previous posts that your better off to avoid the XLR just to make sure. I was in the shop when i looked up the specs, and a full circuit diagram. I think I googled the model number with words like manual and phantom power. They were on 3rd party retail sites, happy hunting.
 

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