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Chewlix custom audio buzzing - ground loop?

tDRG

tDRG

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I have a Chewlix that I'm just using with an external PC. I removed all the stock electronics, wired up my own speakers with an audio amp, and connected it to my PC monitor with a 3.5mm audio cable. I have the amp and monitor powered off the same power strip I stuck inside the cabinet. When the monitor's on and connected, I hear a noticeable hum (video below). I hear it on top of audio as well. When the power to the monitor is unplugged, it seems to go away. I still hear very slight noise, but my phone microphone didn't seem to pick it up. I tried installing a cheap ground loop noise isolator between the audio amp and long 3.5mm cable, but that makes the noise twice as loud. Any suggestions? I can try more tests, let me know what would be useful. Moving the power strip around inside the cabinet didn't seem to have any effect.

My parts:
With the monitor off:

With the monitor on:
 
It could just be garbage shielding on the audio electronics in that monitor as its probably the cheapest part of it and only installed to tick a box.
Also bear in mind the audio from the headphone socket is not line level, it will already be amplified to drive a set of headphones. So while it will still work it is hardly ideal supplying your amp with an already amplified signal.

I'd look into something like this:-

https://www.aliexpress.com/item/100...248398647!sea!AU!0&curPageLogUid=bHcQsDlsZeDZ

Fit it inline with your HDMI cable, it has video passthru to the monitor but breaks out the audio to digital/analog line level which you then connect to your amp. While it may be off aliexoress I suspect the components are still better than what was fitted to a monitor for a headphone output.
 
Ah displayport yeah I didn't consider that just assumed HDMI. You are right the headphone jack is a convenient solution and it should work even if not ideal. Have you got any speakers or headphones you can plug directly into it and see if that buzzing is still there, just to check the socket is working all good and you aren't chasing your tail.
 
Yeah, definitely worth doing a few more tests. There's still some noise when the monitor is disconnected from the 3.5mm and its power but its AC adapter is still plugged in. The noise decreases when I connect my phone to the 3.5mm, and it sounds fine when I play audio through my phone. When I touch the outside of the disconnected monitor AC adapter barrel jack with my thumb while the 3.5mm cable is connected only to the audio amp, the noise noticably increases.

I had tested quite a bit during assembly. No noise with my phone and the audio system. I don't remember any noise when the monitor was powered at the wall and the audio system was powered from the internal surge protector. No issues when I used headphones and the same 3.5mm cable to listen to the monitor directly.
 
There's some noise with the monitor powered off, so I think it's the audio amp. Significantly worse when the monitor is connected. The ground loop isolator didn't make it worse when I connected it to the monitor side, but the audio was a lot quieter and not any less noisy. I'll investigate a different amp and maybe a different 3.5mm cable.
 
Is that with the monitor off but headphone lead still connected though? or with it unplugged at the amp end? if not unplug the 3.5mm lead at the amp end and see if it goes away I suspect it would
 
It actually gets worse with nothing connected to the amp's 3.5mm connection.

Scenario 1: Monitor on, audio amp on, monitor 3.5mm out connected to audio amp 3.5mm in.
Slight noise, actually not that bad. More white noise than high-frequency buzzing. My PC fans drown it out and it doesn't sound bad when audio comes out of the speakers, it's just noticeable when nothing else is on. I might leave it as is and power everything down when not in use instead of just letting the monitor go into rest mode.

Scenario 2: Monitor on, audio amp on, 3.5mm cable disconnected from audio amp.
Loud high-frequency buzzing. Very noticeable.

Scenario 3: Monitor off (power disconnected from power strip), audio amp on, 3.5mm cable disconnected from audio amp.
No change from scenario 2.

I don't know if it's possible to completely eliminate the remaining noise, and I think that's OK. Someone online did recommend grounding the monitor to the frame by running a wire from one of the VESA mount points to a metal area on the frame. Would that help anything? The power strip rests on the particle board inside the cab and isn't grounded. Audio amp isn't explicitly grounded, but I guess the speakers make contact with the cabinet frame through the front plates.
 
I would try a different amp. I've been happy with these. https://a.co/d/9OtdSIh

You could also try using a different audio output from the PC rather than dp, like a USB sound card, optical with a cheap dac, or 3.5mm.
 
Cool, thanks for the recc. I've seen people recommend that one in the past. Yeah, I think the remaining noise is from the monitor's audio out since it's just meant to drive headphones. Bypassing the monitor would fix it, but I think it's good enough at this point.
 
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