Static/Crackling Noise in HTPC Set-up (Grounding?)

[enigma54]

With a lot of help from you guys here on SPCR, I've been enjoying my mini-ITX build (viewtopic.php?p=474898#474898) for over a year now. I've run into a new problem in the form of static/crackling noise coming through my speakers since moving the rig to my home theater set-up.

Specifically, this mini-ITX HTPC is hooked up to my a/v receiver through HDMI. The other HDMI inputs are taken up by my cable set-top box and PS3. When the HTPC is on, the static/crackling noise is coming through my front, center, right speakers as well as the subwoofer. The speakers and subwoofer are hooked up to the a/v receiver, not to the HTPC. The noise seems to get louder when I'm running XBMC or using Media Player Classic to play back mkv's.

I suspect this might be a grounding issue? There definitely seems to be some interference that's causing this noise, almost like it's a ground loop hum, except it's not a hum, but intermittent static/crackling noise through the speakers and subwoofer. The plug for the picopsu power brick is a 3-prong plug. I'm not sure if there is proper grounding in how I've hooked it up? I know that when I connect the adaptor to the inlet of the picopsu, I notice a momentary buzz or spark as I insert it. I've read that using a cheater plug is a bad idea as it might result in electrocution.



Can anyone help me troubleshoot this? I honestly don't know where to start. I've tried plugging the HTPC into a surge suppressor and into a dedicated circuit.

Thanks!

P.S. I should mention that I have an external multi-channel amp connected to the pre-outs of the a/v receiver. When I use the a/v receiver on a stand-alone basis without the multi-channel amp, there is no issue.

[enigma54]

I tinkered with a few things tonight and when I removed the HDMI cable connecting the HTPC to the receiver, all the static/crackling noise disappears. In fact, when I'm watching a blu-ray on the PS3 or watching TV using the STB (both are connected to the receiver via HDMI), and the HTPC is off, there is no noise. When the HTPC is on, however, the noise is there when I'm using the PS3 or the STB.

I'm using monoprice.com HDMI cables for all 3 connections and I don't have another brand of HDMI cable to try right now. I did try swapping the HDMI cables, but that didn't solve anything. So, it's either a simple case of getting a better shielded HDMI cable perhaps or there is something else going on with the way I've assembled the HTPC that's causing it to transmit static noise via the HDMI cable. I'm also suspecting there may be a ground loop somewhere even though I had the cable technician ground the outside cable to my hydro box.

Pretty frustrating to troubleshoot though Any help or advice appreciated! Thanks!

[jhhoffma]

Sounds like a driver or configuration issue to me. A bad cable could cause the issue, but unlikely. Maybe a bad connector on the mobo.

It's not likely to be interference if the signal doesn't travel in an analog form. Did you ever have it working with HDMI without crackling.

I had an issue with my laptop (IDT soundcard) crackling sound that I learned came from some "sound enhancement" options in the drivers. Disabling them got rid of the problem Also, try different options with the sample rate and bit depth of the HDMI output. Your receiver may just have an issue decoding what your mobo is sending.

[enigma54]

Sounds like a driver or configuration issue to me. A bad cable could cause the issue, but unlikely. Maybe a bad connector on the mobo.

It's not likely to be interference if the signal doesn't travel in an analog form. Did you ever have it working with HDMI without crackling.

I had an issue with my laptop (IDT soundcard) crackling sound that I learned came from some "sound enhancement" options in the drivers. Disabling them got rid of the problem Also, try different options with the sample rate and bit depth of the HDMI output. Your receiver may just have an issue decoding what your mobo is sending.

Thanks for your reply. I ordered a ground loop isolator to try but I'm still waiting for the shipment to arrive. In the meantime, I'm more and more convinced it's the HTPC that is the culprit. For example, I unplugged the HDMI cable feeding into the HTPC and fed it into my Seagate media player - no hum or crackling noise. When the HTPC's hard drive is spinning, such as when copying files or unzipping, the frequency of the crackling/static noise that I hear through the speakers changes and it's almost like the hard drive noise is being amplified through the speakers. Also, when I turn on the HTPC, there is a "thump" sound that gets transmitted through the speakers. In the picture that I posted above for the picoPSU connection, there is a little tab with a notch on it (not shown on the photo) and I'm wondering whether that is something I need to ground? This is the first time I've put together a system using a picoPSU so I have no idea if there is anything "extra" that needs to be done other than making the connections. Sorry, I'm not overly technical, but this static noise is driving me bonkers and renders the HTPC next to useless! But I'm pretty sure it's the HTPC causing it and I don't know what the fix is - can someone please help?

[b_rubenstein]

First you need to understand what a ground loop is so you can move on to fixing the actual source of the problem.

http://en.wikipedia.org/wiki/Ground_loo ... tricity%29

[enigma54]

First you need to understand what a ground loop is so you can move on to fixing the actual source of the problem.

http://en.wikipedia.org/wiki/Ground_loo ... tricity%29

Thanks for the link. I have googled and wandered around various forums and other places reading about ground loop hums, scrolling horizontal bars, 60 Hz hums, various isolators, etc. to try and tackle the problem at the source. After some reading, I can't say I have a good grasp of the first principles of what a ground loop is...sorry, it's not for a lack of trying.

Tonight, I did hook up a Revo 3610 in place of my HTPC - no hum/static/noise whatsoever! So this has to point to my HTPC and possibly how I assembled it that is causing this problem. Is it the power supply? Or is it some kind of grounding issue?

Thanks in advance for any input!

[jhhoffma]

Again, your issue is not likely to be hardware related, unless you have a faulty connector. You efforts would be better spent trying to understand what sound configurations you can change that might eliminate the problem.

What codecs are you using to playback media?

FWIW, the thump you're hearing when turning something on is your analog connection from your A/V receiver and your amp. Your amp does not contain a mute circuit to prevent power going to the speakers before receiving a signal.