Interference on line out going to hifi

[ahardy42]

I've got a Z370N Wifi and I want to use it to deliver digital music to a high-end hifi amplifier.

The sound that it delivers has a low volume hissing and cracking type of interference that ruins sound quality.

This is a replacement system for an old ASUS motherboard-based system, which produces flawless sound.

What can I do to improve the situation?

I've already tried a USB DAC which didn't help much. I've also tried grounding the PC case, which also only makes a limited difference.

Thanks!

[shadowsports]

Greetings,
Not a whole bunch of information for us to go on.  So you are using analog out to what type of input?

You might be better off using SPDIF out (header on the board).

Possible causes:
Quality of cable
impendence
Driver version
Driver settings
Hardware incompatibility

[ahardy42]

Hi,
thanks for the reply.

I'm taking the output from the green line out jack and feeding it into the amplifier AV stereo input.

I'm still learning about all the tech behind digital sound production - with my last PC, I didn't have to know anything since it worked flawlessly as soon as I plugged it in, nice for me back then.

So if I used the SPDIF Out, does that mean I've have to get a sound card to pipe it through to the outside?

You mean something like this: https://www.amazon.co.uk/Ex-Pro%C2%AE-Analogue-Digital-Converter-TOSlink/dp/B009K55TJI/ref=sr_1_44?s=electronics&ie=UTF8&qid=1536917553&sr=1-44&keywords=RCA+to+spdif

Doesn't that mean I'm wasting the onboard sound card?

You mention cable quality - but it's not really a continuous noise that would suggest that, I talked to people with experience in this area and they said it's noise coming from the CPU power itself on and off, because the noise varies with what I'm doing on the PC.

Impedance - what is that? Can I measure it or fix it?

The driver version or settings might be the cause. I'm using Ubuntu Linux, the installation detected the sound card and installed the driver automatically.

I asked on AskUbuntu first, and got the  response that this was some sort of ground loop or motherboard defect. I only got the one reply, so it may have been one of  the sound driver developers  themselves who wasn't prepared to admit the possibility of their own efforts being error-prone.  Check here if you want:

https://askubuntu.com/questions/1071245/ubuntu-installation-audio-crackling-hissing-related-to-mouse-keyboard-and-gui

Hardware incompatibility is the last on your list - which bits of hardware could be incompatible? I'm looking at the idea  of buying additional hardware e.g. a DAC or stuff like this:

https://jcat.eu/product/usb-card-femto/

which I don't want to splash out for without really understanding  whether I need to or not.

[shadowsports]

I used this:

https://www.amazon.com/gp/product/B01LWNKIKN/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I had to move one of the PIN outs to match the header.  I used a toothpick. 

Your device might work too, but whenever you introduce a powered device, there is a risk of interference.  I think the drivers and a lack of isolation are very possible causes of the sounds you are hearing.  Have you experimented with others? 

Google impendence.  It is similar to resistance, with the addition of phase.

[ahardy42]

I read up on impedance and SPDIF and hardware and came across stuff on ground loops  which accurately describes  the symptoms I've got. So it seems I could go for SPDIF if I purchase on of these adaptors you mention. I'm slightly worried about SPDIF though as some of the links describe it as problematc and it sounds like it might butcher some of the low volume classical stuff I listen to.

Maybe I'm better off trying to hunt down the ground loop issue, but a couple of things worry me about that - firstly there was no improvement when I grounded the external chassis to earth - and secondly my headphones don't appear to be effected by the poor noise quality when plugged into the same line out.