Buzz and Hum when the module is off. Is this 'Ground Loop'? Asking for solution.

[tiger150]

Hi. Everyone.
I have been using Drumit 5 kit at home for practice purpose for years. I really enjoyed..
So I recomand Drumit 3 module to my church setup.

I recieved it couple weeks ago and set it up with our mixer.
After testing and finishing the sound setup, when I turned the power off of the module, our mixer started recieving loud hum and buzz noise through the channel from the module(Ground loop?).

It was very strange, buzz is feeding when the power was off.
I placed the power line away from the cables
and unplugged the output cables from the module.
It stopped the buzzing.
I believe it is something to do with the module and cable connection.

I researched the forum and youtube to fix the issue.
It seems impossible to find right information to remove the noise.

So far, we decided to let the power on during the service because No Buzzing or Hum coming through as long as the Module's power is on.

Although I still want to fix the problem.
I tried 'Ground Loop Isolator' didn't work.

Module is connected to MIXER by 2 TR cables from OUT1 and OUT2.(About 24FT distance.). And recieving the 'Line in' from the Mixer by TS as mono.

I set UNIT-OUT according to the manual.
"Situation 2 â€" Live 1: Mix for the PA, click and monitor signal on the headphones
In this setup, you want to output the drum signals and songs as a stereo mix. At the same time you want
to use the DrumIt Three as "in-ear monitor station" (stereo mix, metronome, external monitor signal).
For this, you connect the output jacks OUT1·2 of the DrumIt Three with an external mixer and
simultaneously the monitor output of the mixer (Aux) with the line-in jack of the DrumIt Three module.
On the headphone output are now the signals of the DrumIt Three (drum channels, metronome, song
player) plus the external monitor signal (e.g. vocals, bass, guitar).
For the stereo output, use the SUB mix. So that neither the signal of the metronome nor of the line-in
channel are in the stereo sum, the respective sub-groups are switched off"

We didn't have long enough TRS cables to try out yet.
But Direct Box with -20db worked to make the hum goes down. (not perfectly.)

I wonder anybody encountered same problem and solved it.
I read someone says in the forum older manual says to use TRS cable on OUTs on the module. I just want to figure it out before I order TRS cable if I really need it to solve this problem.

Thank you..

[paulf707]

Balanced (TRS) cables typically help with reducing hum picked up by longer audio cable runs, but I don't know why turning it on/off would make any difference...
Have you tried turning off / removing the Power Supply when the kit is off - does that make any difference to the hum?

[Rmiller]

Definitely the cables. Need good TRS cables not TS cables.  TS cables will pick up any stray RF signals whether powered or not. Even though the module is off but with the mixer powered on, you are getting noise thru the cables, especially unsheilded TS cables. It’s rf emissions that the TS cables are picking up from either the mixer or the electricity coming into the building. That’s where power conditioners can really make a difference but still won’t help noise prone TS cables; and the longer the run the worse it is.
Ground loops can make noise worse but TS cables are unbalanced and aren’t grounded so they are always noise prone. TRS cables eliminate noise by canceling their polarity due to the third wire, kind of like an internal ground thus being balanced (Not really a good explanation). They can also be used as a single unbalanced stereo jack thats normally found with headphones.
All cables connected to the module should be TRS, even the line in. Also check the input gain at the mixer. Too high will cause noise whether the module is on or not.