Grounding Question for Passive Mixer

[Ian MacGregor]

Hello all,
I'm currently designing a simple PCB for a passive mixer (16x2) similar in concept to the RMS folcrom (has stereo inputs and uses a mic pre for makeup gain). I am starting to get confused on how to arrange my ground scheme. The inputs will be from a Pro Tools HD192 and balanced line level. The stereo output will be on XLR connectors and will also be balanced. My main question is: Do I need to connect the ground coming from Pro Tools to the the ground going out of my box?? I hope this isn't too confusing. I suppose I could post a schematic if anyone is interested.

A side question, if I do need to connect the "Input ground" to the "output ground": Should I only use the ground of one of the Inputs, since they would be connected together inside the HD 192 anyway? Would connection of all of them together inside my box result in loops??

Thanks a ton,
Ian

 

[Guest]

[quote author="Ian MacGregor"] since they would be connected together inside the HD 192 anyway? [/quote]
Put tranformers to the all input of the HD 192.
OR... disconnect the wires to the HD and leave one connected. If
hum vanish, grounds inside HD are connected.
xvlk

 

[Ian MacGregor]

[quote author="rf"]Hi Ian

I have built several of these... I connected all the grounds together, then connected them to the chassis on the first units... It works fine, but the convention I use now would be to connect all the grounds on the inputs and have the grounds on the outputs on a switch or jumper pins. Also, break the shield connections in the cables at the outputs of your HD192 interface.

rf[/quote]

Thanks for the relpy! I do have a jumper between the input grounds and the output grounds. I am a little confused when you say: "Also, break the shield connections in the cables at the outputs of your HD192 interface."

Thanks,
Ian

 

[rich]

In a studio and live sound I thought it was conventional to disconnect the grounds on the recieving end? By the way just so no one newer gets into trouble, line level only.