Noise from HDMI port, Pi2, HiFiBerry DAC+ [SOLVED]

[rastus]

Hey, re HDMI issue.... could this be something to do with CEC via HDMI? Isn't the latest version of RuneAudio sending a signal to the TV? I know since installing the latest version of RuneAudio that when I turn my Pi on, with HDMI cable attached, because I also use it for watching movies (OpenELEC) that the TV comes on when the Pi is turned on. I will have to test this, run the Pi with no HDMI cable attached, see if it sounds any better.

[PeteB]

At least one of the two monitors I tried was definitely not CEC compatible, so this would not be the main cause. A TV can turn itself on when it detects a signal on the HDMI port, or switch its input to that port, without complete CEC compatibility.

My knowledge of HDMI is pretty limited. I am just a plain old EE, and to understand HDMI fully, I believe only a degree from Hogwarts will do...

I have now been told the HDMI implementation at the Pi end cut some corners in the interest of affordability, with the assumption that the Pi would not be connected to another ground, but float on its isolated wall wart supply (yes, we are back to the supply). When we connect the DAC+ RCA cables to a power amp, there is a potential problem. I can't find a schematic to confirm.

In my case, when I connect the output of the DAC+ to the USB sound card, and from there to the PC USB port, and to the charger, and a a wall socket, a ground loop is created. I will test for this by end of this weekend. (still looking at your links about network software, too).

[rastus]

[PeteB]

Well, it is not the power supply, at least not the stock Pi 2 supply or either one of the other two I tested with. At least not the supply for the Pi. The Pi p/s makes a very small contribution to the noise, almost not measurable (with what I have to work with).

I did a lot of testing over the weekend, and I am still looking over the results.

Tentatively I think I have a combination of a ground loop, and some additional noise, but I cannot sort it out because as potential noise sources are disconnected, this also breaks the ground loop (if any). If I feel there is a conclusive result, I will post more, in the meantime I have a lot of numbers to crunch (sigh).

[rastus]

[PeteB]

[PeteB]

I am calling this "solved" because it is not a RuneAudio problem, and because I think I am posting about issues with HDMI, noise, and audio that have been documented and well covered in other places.

Using a DIGI+ with transformer isolation fixes the problem. Carefully removing or isolating noise sources reduces the noise close to un-measurable.

[urchin.us]

Better late than never....As stated above the problem is likely related to something called a 'Ground Loop', simply use a ground lift adapter on your monitor power cable, or you can actually just pull the monitor ground cable pin on the power cable (Not recommended....but this how I fixed the problem on my end).


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