Troubleshooting an install in a brand new house.

There is a ground loop coming through the sub (Current Audio FLSUB10). At first we thought it was a defective amp on the sub and Current Audio sent us a new amp. Installed the amp and issue still is present.

The sub is connected to a Denon AVR-X2400 approximately 70' away.

After more troubleshooting the ground loop is being introduced through the HDMI cable connected between the cable box and Denon amp. Tried multiple different HDMI cables (6' HDMI cables, a couple no name and Crestron cables), and a couple different cable boxes and still obtaining the same result (sorry didn't get the model of cable box but they are Cisco 4k PVR and non-PVR boxes).

Also tried different inputs on the amp and still the same result. As soon as the HDMI cable is disconnected from either the cable box or Denon amp the loop disappears.

I have tried grounding the incoming cable feed (provider didn't ground it), ground the chassis of the cable box, and ground the chassis of the Denon and still did not correct the problem. The Denon and cable box are plugged into a different circuit than the sub.

Only solution is to temporarily remove the ground on the subwoofer so the home owner doesn't have to listen to a hum from the subwoofer.

Looking for a proper solution that is cost effective as we will be the ones paying for it.

We have the same installation in another house using the same equipment and are not getting a ground loop (houses are a block apart).

Have had similar issues. Try removing the coax from the cable box while everything else connected. This is where I have found most of the ground issues.

Jensen Transformers sell devices to fix ground issues for almost any connection. You may also need a power conditioner device for the AV and Sub. Do NOT cut off a ground pin on the AC plug.

Good luck and let us know what happens.

Check that the coax splitter is grounded.

My vote is also a poorly grounded cable box. Assume this is the issue until proven otherwise. Mr. Brad's diagnostic (remove cable feed from cable box) is an easy diagnostic. A "ground breaker" in the cable feed can be effective, but be sure to check all aspects of cable service because some of the ground breakers will limit bandwidth. MOCA signals don't always survive.

How did you ground the cable feed? Did you connect the splitter to the electrical ground? This usually solves it for me

Try powering the sub woofer off of the same circuit as the receiver using an extension cord. I have had experiences where if the two circuits are on opposite phases of the panel you get noise. It might be as simple as moving the breaker to a different spot to fix it.

Edit. Also most of my ground issues have been cable box related. Xantech used to make a isolator for the cable line.

I hope Current Audio put you through several paces to try to eliminate this problem before they spent their money on an exchange! Most of what is suggested here should have been suggested by them.


But wait, there's more! The cable is connected to the cable box. The cable box is connected to power. The cable box is connected to the Denon.

When you disconnect the HDMI cable, you disconnect the cable box from the Denon. You disconnect the cable ground from the Denon. You disconnect any hum that might be caused by the power connection, too. In short, disconnecting the HDMI cable disconnects several things.


That's the second place you should have looked. The first place would be the cable connection itself, by disconnecting the cable from the cable box.

The third thing to do is to introduce an audio isolating transformer between the Denon and the subwoofer. Put it at the sub end of the cable. If that doesn't work, put it at the Denon end of the cable.

Basically, keep trying different things. The only thing you should NEVER do is to take the third pin off of a power plug. That can be an actual killer move.


One system had a hum that I could not get rid of. I lucked out in that there was a copper water pipe on the other side of the wall from this system. I connected the receiver to that and the hum went away. (But I had to check several places to attach the ground wire to the receiver -- some places made more hum!)


When you solve this, you will see some subtle difference between the ways the systems are hooked up. You might even have an accidental short to ground in your problem house. (To verify, disconnect all wires from all components and measure resistance from the wires to electrical ground.)

thanks for this reply

If you can't find the source of the hum, either one of these should solve your problem:

[Link: amazon.com]

[Link: amazon.com]

I have used both in the past with perfect results.

I don't know how he got my reply to say this"


but I think it may be the single most important thing I've written here.

How is the sub connected to the Denon? Seventy Feet of unbalanced audio? I see from the specs that this sub does not have a balanced (XLR) input and the Denon doesn't have a balanced output so you either did 70 ft. of unbalanced (Hum, Hum, Hum, Hum, Hum) or you used the speaker terminals (really? People do that?)

I don’t know if I missed reading it, or no one suggested it...

How about swapping the cable box with one of the other boxes? If the problem goes away, well that box is bad. This can go with the power block, that is if the power supply isn’t built into the box.

Also, since the sub and av are on different circuits. Is it possible they are on different panels too? If so, that could be a problem in itself. They could be on the same phase, but different panels. Thus the sub panel can not have the grounded (neutral) and grounding (ground) bonded together like they can in the main panel.

KOT

[Link: jensen-transformers.com]

Did you disconnect the coax at the demarc box? If you do that and the hum stops, call the cable company and have them fix their system.

If you want a quick fix, go to the closest car stereo shop and buy a ground loop isolator. The second link in kwkshift's post is just that and you should have at least one in your van, anyway. A company called PAC has them and they even provide a small boost, to make up for losses along the way. Not that 70' is really 'long', but for an unbalanced line, it's pushing the limit without a line driver of some kind.

The need for an isolator (or the more expensive fix of changing the sub circuit's assignment in the breaker panel, so it will be on the same phase) is easy to determine- unplug the cable and if the noise stops, you need one but first, unplug it and connect a test light between the shield of the cable with the shield of the sub's input- if it illuminates, you have a ground loop or leakage. Repeat by connecting to the center lead and input + on the sub.

a couple of changes for clarity....

wait wait wait wait wait wait...

What voltage test light? 12 volts for car use? Neon? Plain old 120V light bulb in a socket? It's possible to have current flowing through a ground and creating hum, but with too little current to light any actual bulb. More details are needed to this right.