Problem with Hum (ground?)

  • Thread starter Thread starter bdemenil
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bdemenil

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I'm having a realy bad problem with hum. I'm using a Mackie 1642VLZ and a PC equiped with a delta1010. The direct outs from my mackie are feeding into the inputs of my delta. I'm using 1/4" (TRS) mono patch cables.

First I disconnect the mixer from the sound card. Now If I monitor the output of either mixer or soundcard, I get only a slight background hiss.

Now I connect the outputs of the mixer to the inputs of the soundcard. The first connection introduces a hum into both the output of the mixer and the soundcard (even if the output of the soundcard is not going back to mixer). With each successive connection, the hum gets louder - in each of the connected channels. On a 4 track recording, the humm adds about 20db of noise. If I turn of my mixer, the hum still comes from the soundcard. If i unplug my mixer, the hum goes away.

I tried switching to my old delta66. It made no difference. I tried switching to a different PC. I tried sitching to my old mackie 1202vlz - neither made any difference. I tried using different outlets in a different part of the house. I tried using a line conditioner. None of this made a difference. I figure there must be a problem with the grounding or with the way I've wired my equipment - but I don't see what it could be (all my outlets are grounded). Anyone have any ideas?

Ben
 
Make sure all your gear is connected to the same ground circuit, sounds like you might have a ground loop. Just plug eveything into a power strip and into the same outlet to see if that fixes it, if you are using a UPS for the PC take it out for the duration of this experiment. If with all the gear plugged into the same circuit you still get it then it probably cabling.

You say you are using TRS (Tip Ring Sleeve) MONO patch cables?
 
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OK, I'm using unbalanced (TS) interconnects - not TRS - my bad. Using blanced interconnects reduces the hum, but does not elliminate it - still have a ground loop.

Ben
 
What is it like when the computer monitor is turned off?
--Rick
 
Solved

I believe 've solved the problem. Toggled all the switches on my soundcard's breakout box to the out - +10db position. Now there's no more audible hum. Also discovered I should be using balanced connectors.
 
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