Hum Issue...

[jstroming]

Hey guys...

I am having an interesting situation on one of my shows, hopefully someone could shed some light...

I have a severe hum between a video playback rack and FOH audio mixer. I thought it might be that the outs on the video rack mixer are unbalanced, however adding a line balancer (a Whirlwind that also splits the signal) doesn't help. I am running out of the isolated out on the splitter, and flipping ground/lift switches throughout the chain, all to varying degrees of success but nothing that completely gets rid of the hum.

As I was screwing around, I noticed that by shorting pins 2 and 3 on the Direct Out on the splitter (the out that I'm not using), the hum went away completely. Thought this was interesting, and that it might give someone a little insight into the situation. Hopefully someone with a little more wiring background then myself might have an idea.

Thanks for all your help.

-Jeff

[renegadeblack]

Make sure that both your video rack and your audio mixer are both on the same ground. Sounds like what you're having is a grounding issue.

[FMEng]

Please tell us the model number of the Whirlwind gizmo. It sounds like one you are using does not provide isolation.

[jstroming]

Whirlwind LBS:

Whirlwind / Splitters

[Lightguy48]

That splitter uses resistors in it, it does not provide true transformer isolation so you still have an electrical connection between the video and sound systems allowing the ground loop to continue. You would be better off installing a DI box such as:
Whirlwind / Direct Boxes

[Chris15]

Originally Posted by Lightguy48

That splitter uses resistors in it, it does not provide true transformer isolation so you still have an electrical connection between the video and sound systems allowing the ground loop to continue. You would be better off installing a DI box such as:
Whirlwind / Direct Boxes

I beg to differ. The literature specs transformer balancing...

You also don't want to be using a DI box because it is introducing a level mismatch you don't need or want. The more proper tool is an iso transformer, something like Whirlwind / Specialty Interface Devices if Whirlwind's your thing...