A/V Components: Humming Noise

I know we've got a lot of home theater buffs here... Was hoping for some advice...

I have a BST 4 channel DJ mixer (I used to DJ in college) which allows me to mix in my PC, VCR, Empeg, and CD player outputs. Obviously I rarely need to play two sources at a time, but it's great to have audible alerts from the PC over my stereo speakers while I'm listening to music or watching TV.

Anyway, with my new apartment has come a new problem with my setup: noise. I don't know why, but I seem to get a lot of noise on both my audio and video signals in this apartment. I have some pretty long RCA cable runs, and in general my cables are basic Radio Shack jobs, none of those gold plated super cables or anything. Do those really make a difference? Are there shielded RCA cables which are less succeptable to this? The noise is a humming noise that sounds like a guitar amp that's turned way up.

My CD player and Empeg are short cable runs, and they're fine. However, my PC and my VCR in the living room are longer, and seem to have a lot louder of a humming noise. My PC's sound card is a SB Live Platinum, and when I plug headphones in, there's no noise to speak of. Once I run it into my mixer or my stereo inputs, I get noise.

I guess I'm wondering if better cables can fix these problems. I've tried swapping various cables (the ones that will reach anyway) with no luck. Are there other things that could be causing this problem? I've made sure my 4-channel mixer gain is set right, and I've turned off all of my PC's microphone and aux inputs to avoid any problems coming from those. Are there any other typical sources of this humming noise?

Thanks for any and all help, as usual.

Well I do know for the 2 days I was using cheap radio chack RCAs in my car, because somehow my very nice RCAs got broken at the connector, I had horrible alternator whine and depending on the position of the cable I had bad noise. As soon as I bought a nicer cable everything when back to normal.

The humming is a ground loop, you can get those in home systems, too. Check out the avsforum or hometheaterspot.com for tips on solving ground loops in the home.

A better cable may help, but if the hum is that bad then the first thing you should try is re-routing the cables. Especially if the same cables were ok in your old place.

What you really want to avoid is AV cables running close and parallel to power cables. You probably want to try and trace nearby power cables in order to do this. If you AV cables need to cross the power cable, then cross at 90 degrees.

You could also try dropping a small fortune at www.bettercables.com, but there's no guarrantee that this will fix anything. Better to find the disease than treat the symptoms.

<edit> ..or as Tony pointed out, it could be a ground loop. </edit>

In addition he mentioned Anyway, with my new apartment has come a new problem with my setup: noise....

Possibly his earth isn't earthy enough?

I know it ranks low on the list of probability but I have read about people pouring a saline solution in/around their earthing stake to improve grounding.

A similar thought occurs to me, which is that one or more of the wall sockets may be improperly grounded, or possibly not grounded at all. It would be worth checking, if only for safety reasons.

Patrick

Damn... This crap is pretty complicated. The one cable is running through my wall within 5 feet of an electrical outlet.. I fished the wire through the base of the wall so I could get sound output from my TV/VCR. I think I can invest in a better shielded cable, but this cable has to go through the wall because going around the wall involves making it about 50 feet long and wrapping it through a doorway and then the door wouldn't close.

As for the one in my room, I don't know what the problem would be there. It's running kinda near a bunch of other cables, but I've tried to avoid power cords. I haven't noticed much of a difference when I move the cables around to various places, so the problem seems much worse.

I looked at a BUNCH of sites describing ground loops and it looks ridiculously complicated. All sorts of diagrams and talking about kilowats and resistors and transformers. Nowhere in any of the four or five guides I read did it actually discuss strategies for eliminating them that I could understand. Is there a "dummies" guide to properly grounding one's components? I can't believe I didn't have this problem in my old place, I mean I had the very same cables running to the very same components.

I'm rather scared by the concept that my actual apartment has something to do with it. WTF? Wouldn't that affect my other components which are connected by shorter cables, and seem to be fine? This is my first experience with something like this, well, I had it once in the apartment I lived in about five years ago but one day it just went away like poof.

AARGH This stuff should be much easier.

A similar thought occurs to me, which is that one or more of the wall sockets may be improperly grounded, or possibly not grounded at all. It would be worth checking, if only for safety reasons.

Well, that's an interesting observation... Are you a psychic? When I moved in, the electrical outlet that is closest to the cables (about 3-4 feet away, though) had fallen out of the box that it was attached to. I had the maintenance guy come and fix it. I think he would have made sure to ground it if it wasn't, but there's also no guarantee of that....

What could an improperly grounded outlet do to an RCA cable 3 or 4 feet away? I know nothing of electricity except that the lights go on when I flip the switch. Okay I'm exaggerating a little, but although I understand the concept of a device having two paths to earth's ground, I have no idea how to solve the problem, and these guides are too packed with theory and don't really explain how to GET RID of the loop.

Are you a psychic?

I knew you were going to say that

Also, if you go into the kitchen and look in the cutlery drawer (near the sink), I sense you will find spoons, possibly some of them bent.

Anyway. The possible effects of an ungrounded wall socket can include induced noise on audio equipment, mainly because a lot of consumer equipment has high leakage current from the PSU.

IE, in most TV sets, the power supply outputs float at approximately half the ac line voltage. This is mostly down to cost reasons, as a fully isolated PSU is more expensive. The end result is that the ground points on the TV, such as the outer of RCA connectors, are also at half the mains supply although at very low current levels, typically microamps. Enough to feel especially in europe, where half the mains voltage is still 110V, but not normally dangerous.

If somewhere between the offending device and the amp you have a faulty earth, sometimes enough of the leakage current can get into the works and manifest itself as a signal at whatever the mains frequency is, 50 or 60 Hz. It might even be the amp itself that is not properly earthed. VCRs are often culprits in this way as well.

It might be worth trying unplugging everything, then connecting each audio source in turn into the amp directly, with both amp and source powered from the same wall socket. See if any combination hums. If not, add more stuff until the problem comes back.

If you are running anything from an extension cable, that might also have a faulty ground. Also, it is possible that during the move an RCA cable got damaged and has a broken ground connection, which wouldn't help. Check all the cables with a multimeter if possible.

Finally, try plugging everything into a different set of socket in another room.

Oh yes, one final though I just had: If the live and neutral wires were transposed on any socket, that could cause all sorts of strange results under the right circumstances, as could a neutral and earth transposition. I've seen both, and neither is safe never mind useful.

Patrick