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Wicked buzz from my Powered Mackie Thump 15-A's

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randtor:
Hey all,
I've read lots of posts on Vdrum forums concerning ground loops and such. I have a Roland TD-10 into the TH-15's, and when I turn the volume up on the Thumps I hear a definite buzz, like a ground loop. If I turn the Thump volume down and the Roland module way up, I have less hum, but it is still there. I have plugged and unplugged different components, one at a time, and get no change (wireless, direct box, hum debugger). I have also tried a Roland TD-20 as well, with no better results. So, I have eliminated the Roland module, the wireless receiver and transmitter in the Zendrum (Shutting off the Zendrum makes no difference), the direct box, and even tried a Hum Debugger. I hear the buzz from the speakers no matter where the speaker is plugged in.... at home, at a gig, etc. I have tried plugging the speaker into a different outlet than the rest of my components, but no change there either.
I have a powered strip that cost a LOT of $$$ to try and wash the electrical power so it's clean..... no joy. I still hear the buzz,which does go away only when I unplug the cord from the back of the speaker. I have tried a {1/4" /  XLR} wire from the Roland, to the back of the Thump; I have also tried 1/4" from the Roland module to a direct box, and thence one of 2 set ups to the Thumps....(a) 1/4" out from direct box to XLR in Thump, or (b) XLR out from direct box to XLR in Thump). When there is no signal in to the Thump the buzz stops, even with the speaker volume all the way up. I'm no electronic wizard, but it seems to me that it has to be the line IN, and NOT the speaker. Trouble is, how do I find out the problem, and how do I fix it? I think I've tried eliminating every component, and all the cords are new and of excellent quality.
Any thoughts or suggestions are appreciated. Thanks!

Rand

THUMPER:
Im sure you thought of this already but make sure the thumps,roland,zendrum are all plugged into the same circuit/outlet. Thumper

randtor:

Thanks Thumper,
Yeah man, I tried separate circuits, all in the same circuit, with and without an extension cord. Nada.
Is it possible there is some sort of cheap or lousy component in the Thumps themselves, that is allowing this buzz to occur?
After all, I have eliminated any other component. When nothing is plugged in to the XLR, all I hear is a slight normal speaker hiss with the volume all the way up. With the cord attached, I get buzz until I turn the volume down to about 60%.
Rand

DrumWagon:
Sounds like a classic ground loop problem.  Do your DIs have a ground lift feature?  I presume you've messed with all the settings there.

One trick I've had luck with (in a studio environment) is to clip the ground connection on ONE end of the XLR cables.  This breaks the ground loop while still allowing the shielding to function as an EM filter.

Another fix would be to pick up some audio isolation transformers, though the better ones can be expensive.

With my laptop rig, I was able to solve a nasty hum problem by clipping off the ground pin of the power brick.  Definitely not recommended for most circumstances,  but worked like a charm and since the brick is encased in plastic and is tucked away where I never touch it, is a reasonably safe solution.

There's tons of info online about ground loops, but here are some links to get you started from a site I found to be helpful:

http://www.epanorama.net/documents/groundloop/groundlift.html
http://www.epanorama.net/documents/groundloop/problem_solving.html
http://www.epanorama.net/documents/groundloop/audio_isolators.html

HTH

THUMPER:
Just had another thought, when my mackie 450 introduuced a hum it was when I had the switch on mic input and not on line input
Thumper

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