BIG ground loop/noise problem here

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sethinspain

Active member
Joined
Dec 18, 2011
Messages
36
Hey guys,

Really been loving the great free-reading through-out this entire site but it's time to finally post something! Hope you've got some time to help me work through this because I couldn't find too specific of information about it on the web for my situation.

I found a bargain Emu 0404 USB (creative labs has recently stopped production of the unit so NO customer support) and after opening it and getting it working in about 10 min with Nuendo, I noticed a problem that we all very much hate in the audio realm - a nice ground hum (I believe) and some hiss. 

I had only connected a 1/4" cable from my guitar direct into one of the inputs and heard both a hissy electrical interferance type sound PLUS a deep hum.

If I separate the EMU from the laptop, no more hiss, but the ground sound is still there.  If I plugin JUST the emu (externally powered by a 5vdc power supply, not usb powered) and plug in my headphones to listen there is no hum and I have to crank the gain to more-or-less the maximum 65dB to hear ANY hiss - the hiss probably from the cheapo pre amps.  But the second I plug in a 1/4" jack the hum shows up.  The hum changes volumn by moving the cable around.  This is just by plugging in the cable yet not connecting it to my guitar or any instrument.  Once I plug it into my guitar, the hum dies down a bit but can still be heard.

Weird part: when I touch the USB output port on the back of the emu with one hand while I'm touching my guitar with the other hand (I think I was touching the strings) the hum stops.  This is probably electronics 101 or something.

I tried with 3 different 1/4" cables, thought they were balanced but I can't guarantee it - maybe this is proof they are not.  I tried also with 2 different guitars, alternating cables, alternating plugs(changing rooms), trying with a 3 plug extension, and same thing.  I even brought an amp over to try and see how it did and same situation; just plugged into the wall with my headphones listening is clean, add a cable and I get a hum, though not as intense as with the emu.  If I take the other end of the 1/4" cable from the amp and dangle it over the laptop I get the hissy sound.

I have used one of the cables with a pure usb powered audio interface, an edirol ua-25 I believe, and had no hum/buzz/noise of any sort.

There are ground switches on the bottom of the EMU for each channel in case of groun loops, but when I switch them on it only increases the hum a LOT.Haven't tried a mic yet so can't confirm how that is.

I have been beating my head around this thing and can't figure out what's going on here.  Could this just be a problem of interferance and needing to spend some cash on high-quality, shielded 1/4" cables?  Power conditioner?  New only-usb powered audio interface?


Any help would be greatly appreciated.

Thanks,
Seth
 
Im a little confused... you're trying to use a balanced 1/4" cable with a guitar?  (balanced is TRS (tip ring sleeve) )  A guitar is UNbalanced and should only use a TS (tip sleeve) cable unless you have some kinda pre built into the guitar (which usually is still an unbalanced out)
 
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