Karaoke Forums

OK so originally I was going to write a long explanation explaining how grounds affect audio systems and how ground loops develop as a result. But then I realized, it was getting wordy and technically burdening so forget it. Here it is in simple terms.

The ground path of your equipment is connected through every piece of equipment that is a part of the system. Each cable has a ground connection (usually the shielding but in some cases it's own conductor) that electrically connects the ground of one piece of equipment to the next. Ultimately these connect electrically to the earth through the grounded plug that is plugged into the electrical outlet. If there is more than one connection to earth amongst all the equipment and if they have different resistance, it can result in a current forming between the two ground points which will then run through the entire ground path of your rig. Since A/C current in the US alternates at 60Hz, the resulting voltage causes a 60Hz hum in the system.

The key to eliminating ground loops is to ensure that there is only one path to the earth for your ground chain. The easiest way to do so is to ensure that all of your equipment is plugged into the same outlet. This ensures that all equipment has the same path to ground and so no potential for a unintended current exists. If this is not possible, the next option is to ensure that the ground of each outlet is at the same potential. This is easier than it sounds because the potential of the ground connections can be affected by wiring, other items connected to the same circuit and other interference obsorbed by the ground along the path.

So if you have to use multiple outlets and can't ensure the potentials are the same between the two grounds, the next option is to isolate the two paths. This is where a ground lift TRANSFORMER comes in. A ground lift does not simply cut the ground path (i.e. using a 3 prong to 2 prong adapter is not a ground lift), instead it uses a transformer to provide a continuous ground signal without actual electrical connection between the two ends of the ground path. This is what the HumX and similar devices do. This ensures that you have the proper ground reference and electrical connections necessary for proper and safe operation while isolating the ground path to prevent unintended currents from developing. Each piece of equipment that is plugged into a ground source (outlet) must be isolated from the equipment that is plugged into a different ground source. Remember, even if your equipment doesn't have a grounded plug, it still has a path to ground through the audio or video cables it connects to other devices through. So this is the challenge, how do I isolate each of those paths with a transformer.

Some pieces of pro-audio gear have built in ground lifts with a switch to engage them. DI boxes and amps commonly provide this functionality and it is a great way to isolate the ground paths in your system.

Now believe it or not, this is over-simplified and I'm sure the electrical engineers out there are cringing at my sloppy use of terminology. But I fear this is already still quite difficult for many to understand so I'm hoping this is just a starting point for further discussion so folks can actually learn about what a ground loop is and find proper and SAFE ways to deal with it.

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DJ Tony
Let It Rip Karaoke

OR......if your equipment i.e Laptop,s power lead has an earth fitted all the way From the power outlet to the mixer, (some don't..some do)...then you will experience interference due to the reasons set in the previous post..... The only way to get out of this is to buy a "Ground earth isolater" from your electrical component retailer (Maplin in the Uk...Radio Shack is it in the US????)). DON'T CUT OFF THE EARTH PIN ON THE PLUG (as some have unbelievably done!)

Your best option is always to plug everything into the same outlet (i.e. Use a power strip, rack rider, etc). Given the physical proximity of the laptop to the mixer in most cases, there's no reason they couldn't be on the same outlet. Honestly the only time I've ever not been able to do so with my Karaoke rig is at one bar I play regularly where the house TV that I connect to is plugged into a different circuit than my equipment. The ground that carries from the TV, through the RCA cable, to my video converter through the USB into the computer causes ground loop voltage (and the associated Hum). A perfect example of how all of the interconnected devices share a common ground path (who'd have thought the ground would be carried all the way through those different paths and devices).

If in your example above, you absolutely cannot get the laptop and mixer on the same outlet (i.e. or more importantly the same electrical ground) then yes the isolator would be the next step. However that should only be the second option.

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DJ Tony
Let It Rip Karaoke

A better choice would be a transformer isolator for the TV signal, but these devices are surprisingly hard to find. They are made though, I searched The Google a few months ago and did find a few.

My guess is that TV distribution amps, the kind large venues use for sending the same signal to dozens of TVs, probably have this built-in to prevent ground noise from interfering with the TV picture and audio.

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Jeff Wheeler, moonlight DJ/KJ

Agreed about the isolation transformer. I've found plenty of them for Coax connections, however I've not had any luck finding them for RCA or VGA connections (which are what I use). If you find one for either of those types, let me know I could sure use it.

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DJ Tony
Let It Rip Karaoke

Interesting you should mention this. I had that exact problem after the venue installed the said amplifier and didn't tell me about it. I went nuts trying to figure out why I was getting the symptoms of a ground loop where I never experienced them before.

I did everything I could to minimize the hum at the beginning of that evening, until another KJ from different night told me to disconnect the antenna coax cable from the TV I was plugged into. And by the way, I was connected with video only; no audio to the TV at all. The noise was being carried back to my system via the video wire, through my karaoke machine, mixer, and amp to the speakers.

Well it was just magic. I did as he said and the hum was gone!

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EveningStar Entertainment & Events
JR & Michele LaPorte
Peoria, AZ