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ground loop issue - involving gear from SPL, Audient, PMC, Antelope
Old 3 weeks ago
  #1
Here for the gear
 

ground loop issue - involving gear from SPL, Audient, PMC, Antelope

Dear Gearslutz members,

I'm having a very weird grounding issue in my studio. I tried contacting various support teams already, but no luck. But let me start from the very beginning.

I had no problems when using my Audient ID22 Interface, Adam Sub 8 + PMC TB2S-Aii speakers setup. But the problems started when I decided to upgrade my signal path and purchased the following:

Drawmer CMC2 (monitor controller)
Antelope Discrete 4 (audio interface)

I replaced the Audient ID22 with the new Antelope Interface, and connected it's outputs to the Drawmer, and the Sub and my Speakers to the outputs of the Drawmer. Further, I connected my Daking Mic Pre One to one of the inputs on the Antelope. Suddenly, a very annoying ground loop hum was coming from my speakers.

So at first I was suspecting the Daking Mic Pre, but the noise wasn't there when I connected my PMC speakers directly to the Antelope interface (bypassing the Drawmer monitor controller). So I got a replacement for my Drawmer, as I thought it was broken. However, the same issue appeared with the 2nd unit. As a next step, I returned the 2nd Drawmer CMC2 again and ordered a SPL 2 Control, but again, the same issue.

So I thought the monitor controller can't be the issue here and dismantled my complete system to reduce it as far as possible.

Now here it gets strange. This is the outcome of some different scenarios:

Outlet -> Plugbar (new)
Connected to the plugbar is:

scenario 1

Daking Mic Pre One -> TRS cable (balanced, Sommer Cable) ->
Input 1 of Audient ID 22
Audient ID 22 -> Output 1 -> Balanced TRS to XLR cable (balanced, Sommer Cable) ->
PMC Tb2s-aii

result: no hum coming though the speakers or the headphone output of the Audient

scenario 2

Daking Mic Pre One -> TRS cable (balanced, Sommer Cable) ->
Input 1 of Audient ID 22
Audient ID 22 -> Output 1 -> XLR cable (balanced, Sommer Cable) -> Input 1 SPL 2Control
SPL 2 Control Output 1 -> XLR (balanced, Sommer Cable) ->
PMC Tb2s-aii

result: hum coming through speakers (no matter if the ground lift on the SPL is activated or not)
and through the headphones of SPL, no hum coming through the headphone out of the Audient

scenario 3

same as scenario 2, but PMC speaker not connected to the SPL

result: no hum in coming through the SPL headphone out

scenario 4

Daking Mic Pre One -> TRS cable (balanced, Sommer Cable) ->
Input 1 of Audient ID 22
Audient ID 22 -> Output 1 -> Balanced TRS to XLR cable (balanced, Sommer Cable) ->
Adam a5 speakers

result: no hum coming though the speakers or the headphone out of the SPL if the ground lift on the SPL is activated, hum is present if the ground lift is not activated.

There was nothing else connected to the plugbar (no computer, no display etc.). No mic or instrument was connected to the preamp either.

So it looks like scenario 1 and 4 solves the problem, but both are not optimal because in 1) I'm not able to use my SPL 2 Control (which I need to control my speakers and my sub simultaneously)
In 2) I was using my old Adam A5 speakers as a test. But clearly this is not an option as I love the sound of my PMCs.

By the way, I tried different power cords (and turned them around in the plugbar), and tried different cables (all balanced, high quality manufacturers). I also tried useing a Furman power conditioner, but that didn't help either.

Any help would be much appreciated!
Old 3 weeks ago
  #2
Gear Addict
 
audiospecific's Avatar
 

Does the hum go away when you disconnect the usb to the computer?
Old 3 weeks ago
  #3
Here for the gear
 

Quote:
Originally Posted by audiospecific View Post
Does the hum go away when you disconnect the usb to the computer?
No, unfortunately not. The Audient ID22 Interface wasn't connected to the computer in any of the test scenarios described above.
Old 3 weeks ago
  #4
Gear Addict
 
audiospecific's Avatar
 

Well I didn't want to tell you this first, but this controller fails my qualifications as a universal monitor controller. Because the inputs and output jacks need to have individual pin1 lifts.

get a cheap cable, and cut the pin 1 connection, or make a two wire balanced xlr cable (pins 2 & 3 only). You probably need to lift pin1 on all the speaker outs btw.

By the looks of it the ground lift is just a chassis lift, which would not isolate the ground on the i/o jacks, just lift the ground to the case.
Old 3 weeks ago
  #5
Lives for gear
 
Mundox's Avatar
Somewhat like audiospecific recommended, I would lift the ground on the inputs to SPL and inputs to speakers. This way SPL will be floating with its own ground ref, yet the signal will be covered by the neighbouring ground connections.
This is assuming the chassis are not touching.
Old 3 weeks ago
  #6
Here for the gear
 

Thanks for your input!

So I'd need either something like this: Whirlwind Lifter or solder pin1 of my XLR cables?
Old 3 weeks ago
  #7
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Mundox's Avatar
If you've got the cash and don't mind extra connections in your chain then yeah the Whirlwind is good.
But personally I'd unsolder and seal pin 1.
Old 1 week ago
  #8
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The whirlwind adapters did solve the problem! I connected them to the input of my speakers.

Thanks guys!
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