Interesting Ground Loop

[AnotherJohnson]

I’ve been running an inexpensive Denon AVR in our very modest HT. I’ve been using WiFi, a wireless cable box, and a Sony BluRay/DVD player. The TV is a Sony Bravia. The front speakers are Sonus Faber, the back speakers are PSB Alpha AVs, and the sub is a Revel Performa3 B112 V2.

Dropouts and streaming discontinuities were a problem with Amazon Prime. I brought an Ethernet connection to the AVR, but problems persisted. No ground loops, but intermittent streaming.

So on a whim, I moved the Ethernet connection directly to the TV. The intermittent issues ceased. No problems using the Sony TV as the point for the Ethernet connection. Everything works smoothly … except the sub started to hum all the time. I shut the sub down and the hum went away. Several repowering attempts always brought back the hum.

Wondering if JF’s magic bullet of plugging the sub into the same outlet as the TV/AVR/Disk player would help, I tried it. And the ground loop has disappeared.

So the addition of an Ethernet connection to the TV brought a ground loop to the sub. But plugging everything into the same duplex got rid of it.

[admin]

I suppose any hard connection can cause a ground loop. Ethernet cable does not have a ground wire but would connect two very far away powered units so I can see some grounding issues popping up. Regardless, glad it was an easy fix.

As for the streaming problems via the receiver the first think to check is the connection quality. Not sure if the receiver has any built in connection testing capability. Some equipment are sensitive to very long ethernet runs, especially if there is interference and it's not a shielded cable. When the connection is near the viable point, often some hardware will work well while others start losing connection. I always go for low hanging fruit first when troubleshooting. Running some more advanced network diagnostics via computer on the cable or simply buying an ethernet cable tester would be something to look at first. You can get a cheap tester for like $10 off amazon.

[AnotherJohnson]

No interest in figuring it out further. The cable is 50’ of Cat6. Works fine. I suspect the culprit is some aspect of the sub connection to the AVR brought on by the way the digital feed travels when it enters at the TV instead of at the AVR. I did not change any of the HDMI connections. At least one is an e-ARC (?). Really, it doesn’t make a lot of sense.

The AVR turns on when the TV is turned on. The system figures out that the AVR is on, and it switches the audio from the TV speakers to the AVR. The sub triggers itself on automatically when it senses a signal.

Everything works with no drama or extraneous noise or interruptions. It all powers up and down with the TV remote.

So … I just thought this was interesting. The sub’s power cord was not long enough to reach the outlet at the TV. So it was on an adjacent wall, probably on the same breaker bar at the box. Just like the problems I’ve had with the LP275Ms.

I almost sent the sub in for service, but then decided to try Jeff’s cure all trick. And it worked. Go figure.