Axiom Home Page Forums General Discussion Technical Questions Subwoofer hum - ground loop?

I'm almost certain I've seen this topic here before but I can't find it by searching. I have just hooked up my receiver to the TV, and when I plug the coax cable into the TV I'm getting a loud hum/buzzing from the sub. Seems like a ground loop to me, and I'm looking for suggestions on getting rid of it.
Is conversion of the signal from 75 ohm to 300, and back again, the first thing to try?

If you have an ep500 or and ep600 I would loosen the ground screw on the back first and see if that helps.

If that doesn't work I would purchase the axiom ground isolator.

It is $48 and eliminated my subwoofer hum completely. I even talked my cable company into paying for it after being escalated to a manager.

If you use resistors and rig up something yourself you may fix the problem but will probably lose you picture if you have any HD or digital channels.


more discussion here:
http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=187122&fpart=1

If you have cable, you may want to make sure your incoming cable is properly grounded ... in my case, I ran a 12ga ground wire from the splitter (inside the plastic box in the pic) for the house down to the house grounding rod. Just a month or so ago I noticed a very prominent ground hum and went outside to check the ground, sure enough the wire had somehow worked itself loose from the rod and after securing the wire the ground hum disappeared.



Which reminds me, I *really* need to secure that ground wire to the house one of these days.

Rick lives inside the Matterhorn.

That would be my mancave Sean.

The rocks do look vaguely out of place for here though, whenever we first moved here we pondered what color we should paint 'em, and what exactly were these things anyway, until one of the good neighbors informed us that they were rocks and rocks don't get painted.

So we left 'em as is.

That's great advice--rocks don't get painted! I like it.

I just got the new 350, and I'm not sure if it has the ground screw. Will check when I get home. Also need to confirm that the cable is properly grounded where it enters the house. thanks.

When I added a second sub to my setup I started to get the ground loop hum. All I did was use an adapter for the electric cord...three prong down to two prong... and everything has been fine since! I used the adapter on the ssecond sub which apparently caused the problem.

I would not reccomend using a 3 prong to 2 prong adapter. There is a reason that the 3rd prong is there!

I had a ground loop problem with one sub, which loosening the ground screw would not help. The ground isolator fixed that problem.

When I had two ep500's for the weekend I noticed the ground loop hum slightly came back.

I loosened the ground screw on the second sub and it went away.

So for two subs I need the ground screw loosened on the second one + the ground isolator to eliminate the hum.


It can take a lot of trial and error to finally resolve a ground loop issue.



I would try the ground isolator from axiom- it works great

I seem to have resolved it. Traced the cable back to the nearest splitter and attached a 14ga. ground wire between the splitter and an electrical junction box that happened to be close by.
The hum is gone.

I'll put the ~$50 I saved into my next Axiom purchase, which will probably be a couple of M3s.

Guys - I'm having this problem too, but it happens regardless of input source. For the folks having the problem above, did it only happen when you were watching cable, or the ground problems with the cable affected all sources?

In my case, there is a hum from the sub (Earthquake 12") even when the rest of the system is off if I turn the sub on. I've tried fiddling with the power/sub cable and occasionally it seems to improve, but I can't isolate what I'm doing when it gets better. I figured maybe they just couldn't be crossed, but separating them totally doesn't seem to be the trick.

FYI, the sub wire goes from the AV rack, up a wall through the attic into a wall plate. That part of the run does NOT seem to be the problem as with a certain amount of fiddling with the wires between the wall plate and the sub, the hum does seem to disappear.

Is this something the ground isolator will fix, or are there other solutions I can try first?

What happens when you unplug your coax cable?

my groundloop was caused by my cable- and it did not matter what source I was watching.

If I unplug the coax, sometimes it is better, sometimes it is not... I've actually found that by touching the RCA inputs on the subs with my finger, the hum can be attenuated...

commence jokes about my magnetism, etc....

Seriously though, advice appreciated.

The hum is attenuated because your body acts as a large capacitor to ground. That hum is going right through you buddy. Stop that or you won't be able to have any more kids .

But seriously, unplug your coax right at the entrance to your house and see if that makes a difference. If so, you need a coax ground isolator. Your cable company should provide you one free of charge. It would also be a good time to get your cable levels checked. They had to install and active amp at my house because the levels were so low.

Jason, your last comment that there's still some hum even with the coax completely disconnected indicates that this isn't a ground loop, since with no cable connecting the sub to the other components there's no path to form a loop. If the sub hums in this situation it indicates that an internal defect in the sub amplifier has probably developed. Neither grounding yourself to drain your excessive personal magnetism nor buying a ground loop isolator should help.

I had a ground loop problem with my cable.... The axiom ground isolator fixed the problem.

I told my cable company that I needed a ground isolator and they called out a technician who basically told me he had no idea what a ground isolator was and the problem was with my equipment. He had never heard of axiom or denon, so my 'off brand' equipment apparently was inducing some type of noise.


I bought the ground isolator from axiom and spoke with a supervisor at my cable company and convinced them to reimburse me the $48 for the ground isolator.

I had to disconnect my cable at the entrance into my house to eliminate the problem. Somehow, it was injecting "nasties" into my ground. The ground isolator fixed that.

Thanks all - John's comment seems to indicate I may just have to deal with it until the new EP-600 arrives. The hum is pretty low right now and probably more noticeable because I have the volume turned all the way up on the sub to keep up with the Axioms.

Now... if the EP-600 also hums, we'll have a much bigger problem because a 'small' EP-600 hum will probably be audible from outside the house versus the current problem which is only audible when the room is fairly silent.

When I unplugged my cable and had the ground screw loosened my hum would actually get worse. IF I unplugged my cable with the ground screw tight it would go away

The ground screw is something unique to Axiom subs right? I don't think my EQ sub has one...

Yes it is.