Ground Hum

[asdrew]

Hi, we have a TriCaster that we record Chapel services with at our seminary in Atlanta. We are getting a ground loop hum in the sound that can be removed if we lift the ground to the power cord of the sound board that feeds the TriCaster (& other things).

The sound board is a Mackie 1642 and the installers have connected a 1/4" sub-out to one of the 1/4" mic inputs on the TriCaster (with a 3-conductor 1/4" cable). If I disconnect all other inputs and outputs but this cable, the hum is still there.

Obviously, we prefer not leave our sound system ungrounded, but it's either that or the TriCaster at this point.

I know the sub out from the Mackie is not a stereo output, I assume that the mic in on the TriCaster is not either but I have not found any specs that indicate how the input jack is wired to be sure.

Since the TriCaster mic input on the screen has a L/R balance it is not clear whether it is for input or output (selecting just L or R from a stereo input source, or routing mono input to just the L or R recording channel).

So, if I can know for sure whether the TriCaster's mic input jacks are 2-conductor mono unbalanced, 3-conductor stereo, or 3-conductor balanced I can make the necessary changes in cables, connections, or direct boxes.

Does anyone know for sure how this mic input jack is wired?

Thanks!:beerchug:

[Jim_C]

The sound board is a Mackie 1642 and the installers have connected a 1/4" sub-out to one of the 1/4" mic inputs on the TriCaster (with a 3-conductor 1/4" cable). If I disconnect all other inputs and outputs but this cable, the hum is still there.


What happens if you use a 2 conductor 1/4" cable here?

[lancelewis]

Whenever I get a ground hum in a line that is being fed to my tricaster (or any other equipment I might be using on that day) I put a direct box inline...So you would plug your feed from the sound board into the direct box, and then run a line from the direct box to the tricaster. Direct boxes give the option to lift the ground. Another option might be to try plugging the tricaster into an outlet that is on the same circuit as the sound board. And another possible fix would be two use a three prong to two prong ground lift on the tricaster main power cable. The direct box is the best solution.

[asdrew]

Thanks for the replies.

Those are all suggestions that I want to try out, but I want to be sure about the wiring of the mic-in jack so I can decide which is best to do.

For now, I've used a 2-3 prong adapter to lift the ground on the Mackie, I would prefer not to unground the TriCaster.

My next move if I don't find out about the jack will be to try a 2-conductor 1/4" cable, but I suspect I will have the same result.

If I end up using a direct box (which I suspect is the end solution) I want to be sure about the wiring of the jack first so I can use the proper box and cable.

[asdrew]

The mic inputs are 1/4" 2-conductor mono unbalanced.

I was able to use a 1/4" 2-conductor plug in the sub-out of the Mackie board split into two RCA plugs in the L&R line-in jacks of the TriCaster with no hum.

When I have time I will re-arrange some things in the AV booth and get both the Mackie & the TriCaster plugged into the exact same source and see if the hum is still there with the previous connections.