those pesky ground loops!

[James HE]

(another long and confusing post)

I thought I was a genius!


Ok so I'm taking the l/r RCA out of my TASCAM 424 into my dbx compressor. The signal then goes into a BBE Maximiser (this is usually in bypass mode, sometimes I do useit if I'm compressing heavaly at mixdown). The phono outs on the BBE go into my tape deck and the 1/4 in outs go into the monitor in (via RCA cables and adaptors) on my stereo reciever. Ok so far so good...

I had the idea to also use the XLR outs on the compressor, to send the signal into the next room and into the computer. There isn't really a problem running both outs (i don't think) but when I plug in the cable to the sound card (XLR-1/4 into a Y cable with female 1/4 ins and the 1/8 stereo plug- shew!) whenever I plug it in I get a freakin ground loop hum!

I thought I had finally figured out a way to avoid moving my stuff from room to room but NOPE!

So anyone got an idea about why this is happening. Might this be solved with so better cables? Could I possibly remove the ground at one end to elimnate the noise. ...Also whenever I do move the stuff in to the room with the computer I have to run power from my room to the 4 track and effects and stuff because I get another ground loop if I plug them into any out let in this room- or the bathroom even. (man this place must be wired wierd)

-jhe

 

[James HE]

Well I removed the ground in my room (I just dug up one of those grounded to ungrounded adaptors) And hey it worked!

But alas the XLR out on the compressor defeats the 1/4 out
I can use both outs on the BBE however- so I't off to the store to get some proper cables (I was looking foward to not buying anything and just using my XLR cables though)

And then of course there is getting used to running back and forth between rooms- but that's better than moving equipment back and forth!


-jhe

 

[sonusman]

Hey James, just a FYI thing about ground.

In audio, you have electrical ground for the power, but your audio has a ground too. You knew that.

But, when you have two components hooked together that are on seperated electrical breakers, you are bound to have a ground loop problem. This is because while the electrical ground is seperate (the problem), you are sharing an audio ground. Thus, you have two ground path potentials. This is what causes the hum.

I am sure that someone on here can share a far more technical version of saying the same thing. But the lesson is, try to keep all audio components that share an audio ground on the same electrical circuit.

In effect, what you did was remove one of the potential from grounds by applying the ground lift (your little 3 to 2 prong adapter) to the electrical ground. This will solve ground loop problems most of the time, but not always. Another problem with this too is that now all the components on the ground lifted circuit have no immediate path to ground. In the case of shorting problems, this gear could potential go into melt down.... But, I have never really heard of this happening with audio components. But, I HAVE seen sparks come off of a patchbay from an improperly grounded studio before. The two components that got fried cost the studio owner around $400 in repairs.... I believe he solved his grounding problems for about $500. So, he is out an extra $300 that could have been avoided. A lessen learned really.

Ed

 

[James HE]

Actually in not sure that I knew that...
Makes sense about the audio ground.

Aftering reading your post three times It makes sense

So having all the power on the same ground should eliminate the (electrical) ground loop hum. But what if this is the case and you get the hum- then your problem is the audio ground right? How do you fix that problem? would all the inputs need to be balanced?

Like for instance what would happen when I'd move stuff in here. (I would run all power from the outlet that the computer is on) I'd have the 4 track going into the computer- everthing is fine. But when I inserted the compressor I'd get the loop- (I solved this by running it on power from my room) The compressor is the only thing with balanced ins and outs- would that be the problem?(but that dosen't make sense!)

oh well...

btw... I now have the cheesey stereo Y splitter and two headphone extention cords as the run to the sound card (hopefully this will be only temporary and I'll get a better run)

-jhe