HTPC HDMI Hum....possibly ground loop

[wilco1uk]

HTPC connected to Marantz 6012 via HDMI. Marantz sends Pre-out to Arcam A85/P85 for front three speakers. Marantz, Arcams (and sky box) all fed from one PowerPoint. HTPC, Xbox and TV all fed from a second PowerPoint about 1.5m away so probably a spur from the first.

I get a low volume, low pitch oscillating hum (from the front three speakers only) when the HTPC is doing something on screen. Static image, all is fine, however as soon as the image moves whether it be a movie or a scrolling info window in Kodi, the hum starts. It’s not audible above ‘normal’ sound through the speakers but it can be heard during any quiet scenes.

No problems with the Xbox which shares the same wall power socket as the HTPC.

It didn’t use to do this when they all shared the same socket.

Pretty much all the wires (four hdmi, 6 sets of speaker cable, coax phono, digit coax, several cat5e network cables) between from the front three speakers, TV, HTPC, Xbox, Dac (plugged into Arcam) to the Marantz and Arcam share the same space and also run down the side of the HTPC.

Anyone have any ideas if this likely to be a ground loop issue or an interference issue.

Cheers

 

[Deleted member 39241]

I am unfortunately familiar with these issues, having 5 HTPC's in the house. Is the noise only present if the HTPC is switched on?

These can work quite well between the pre-outs of the AVR and the inputs of the power amp:

https://www.amazon.co.uk/Behringer-...92560&sr=8-1&keywords=behringer+hum+destroyer

The other thing that might work is a fibre HDMI between the HTPC and the AVR, one with no copper at all. I have not tried this yet, so if you do, let me know!

 

[noiseboy72]

Ground loop will normally produce a permanent hum, not one that changes with content or activity.

This might however be interference on the earth line - often called functional earth noise. The earth is used to remove this noise but what can often happen is that the earth is also linked to the shield on the video connectors, so the noise ends up on the audio earth as well!!

Good suggestion on the fibre HDMI, but often it's only the signal that is carried on the fibre and there's still a physical earth connection between the 2. Check when you purchase.

 

[Deleted member 39241]

A common theme that I have experienced with my set-ups is a scratchy variable noise in the tweeters which seems to relate to things changing on the PC, eg clicking on the start menu button. The hum destroyers have been quite good at removing that, although I would not have described the problem as a hum, but sometimes you get a voltage / volume drop as they are passive DI boxes (direct injection). You can get active ones which would prevent the voltage from dropping.

 

[Rodders53]

It didn’t use to do this when they all shared the same socket.

Simplest solution is to revert to this arrangement?

Then see what can be fed from the other socket, one item at a time, to see if the issue returns.

Computers are often a major source of interference and it may be worth going over all the earth/ground connections inside it to ensure things are seated right, screws tightened and shielding metalwork fitted correctly?

 

[wilco1uk]

Thank you, a lot of food for thought.