GROUND LOOP NOISE

[Bill Knight]

I am new to the forum. I am 65 years old and play in a rock band. We use a 32 channel mixer controlling powreed QSC mains, subs and monitors. I can't get rid of annoying ground loop noise. I have had our practice facility rewired to provide 2 separate circuits so that our instruments can power through one and the sound system through another. I was told this would stop the ground loop noise. While improved, it is still there. Can anyone guide me through eliminating, not improving, this noise. I do not know what else to offer so please ask questions if this is too vague.


Bill

 

[WaynePflughaupt]

This is a forum for home theater enthusiasts, but I'll give it a try.

Both circuits should be on the same phase. If not, if there is any wired connection between the two circuits (e.g. a direct feed from a bass guitar amp to the mixing console) you can get a ground loop.

That said, it’s not uncommon for guitar equipment to be noisy, as well some PA equipment. You might unplug everything from the mixer and add in each piece one at a time to determine where the noise is coming in. You can also use headphones at the mixer and solo each input one at a time. That’s a great way to figure out which channel the noise is being introduced on.

Regards,
Wayne A. Pflughaupt

 

[Speedskater]

a] Is the system quit in another building, using the same interconnect cables & musical instrument cables?
b] Try plugging everything into one AC wall outlet. You may have to turn the components on one at a time to not trip the breaker.

 

[highfigh]

I am new to the forum. I am 65 years old and play in a rock band. We use a 32 channel mixer controlling powreed QSC mains, subs and monitors. I can't get rid of annoying ground loop noise. I have had our practice facility rewired to provide 2 separate circuits so that our instruments can power through one and the sound system through another. I was told this would stop the ground loop noise. While improved, it is still there. Can anyone guide me through eliminating, not improving, this noise. I do not know what else to offer so please ask questions if this is too vague.


Bill

Do you have any extremely old guitar amps in this mix of equipment? If so, do any of them have a switch marked 'Ground'? If so, and especially if any part of the audio system is connected to this/these amps, flip the switch. A better choice would be to replace the power cord(s) on the amp(s) with this switch- it can be dangerous, if not lethal.

Disconnect one piece of equipment at a time, to find the offender.

Is this a buzzing sound, or a hum? If it's buzzing, make sure it's not caused by a dimmer for the lights. It could also be caused by a computer monitor or computer, if you use one.

 

[TLS Guy]

I am new to the forum. I am 65 years old and play in a rock band. We use a 32 channel mixer controlling powreed QSC mains, subs and monitors. I can't get rid of annoying ground loop noise. I have had our practice facility rewired to provide 2 separate circuits so that our instruments can power through one and the sound system through another. I was told this would stop the ground loop noise. While improved, it is still there. Can anyone guide me through eliminating, not improving, this noise. I do not know what else to offer so please ask questions if this is too vague.


Bill

We need a lot more information. We need exacting details of all connections. These systems are complex and unless set up by experts are ALWAYS noisy in my experience. I have a lot of experience with this over the years, and still unfortunately get roped in.

Let me ask you a few questions.

Do the speakers hum with no input?

When you connect the mix deck to the speakers, do you get hum when nothing is connected to any inputs and all faders are down?

Do you just have mics connected to the mix desk or instruments as well?

If you do this is problem. I used to solve it by constructing direct boxes using very high end Beyer transformers, which isolated the instruments from the desk. This allowed a line to go to guitar amps etc and a clean balanced feed with mic characteristics to go to a mic input. Using an unbalanced line input to the desk is asking for trouble.

The whole system must have only 1 ground. This is crucial.

Not all hum is a ground loop. A lot of noise is from SCR light dimmers. These are a huge problem. I helped tame the Lutron Maestro line, and I would vouch for them as emitting the least RF. However it is impossible to design a solid state SCR dimmer that does not emit some RF. The bigger the building and the longer the light cable runs the worse it is.

I have had to go the expense in often used venues to use expensive and bulky variable voltage transformers to dim lights.

Modern LED light bulbs now emit a lot of RF which is a big problem.

This is a common and persisting problem with no easy solutions. The solutions are also frequently not cheap.