humming computers (was RE: Kubuntu 18.04 and HDMI

[Carruth, Rusty]

A hum that goes away when you ground 2 machines together is an indication of an issue that really should be addressed and which could even be a safety hazard.

Do you have a meter which you can use to measure the ac potential difference between the computer case and the coax connector (I assume the outer shield! If not, I'm even more concerned...)?

In any case, one possible cause of the hum is 'ground loop', or worse, mis-matched hot vs ground on a non-isolated system (think about the 'polarized plug' - the wide blade is intended to go to 'neutral', while the narrow goes into the 'hot'.  If a socket is miswired such that hot goes to wide, you have an extremely hazardous situation, which I'd expect to melt your wire connected to the alligator clip if it was the case, but still, have to verify all is good there.)

You should probably either fix the hum issue without having to run a wire, or make a permanent connection from the computer to the ground on the cable box.  Probably - I am not a licensed electrician but am a Ham, (and sometimes I play with electricity at home ;-)) so a hum is something I think shouldn't be ignored.

(If the voltage between the pc and the box is 'low' then just running the wire is probably a reasonable option - but again, I'm not a licensed electrician, check with one before making any changes to your 110V circuits!)


Rusty Carruth | Customer Support | rusty.carruth at smarth.com | http://www.smarth.com

-----Original Message-----
From: PLUG-discuss [mailto:plug-discuss-bounces at lists.phxlinux.org] On Behalf Of Brian Cluff
Sent: Wednesday, August 29, 2018 9:26 AM
To: plug-discuss at lists.phxlinux.org
Subject: Re: Kubuntu 18.04 and HDMI

On 08/29/2018 08:58 AM, Jim wrote:
> ... have to use the sound card in the computer.  Because of the cable box, 
> there's an annoying hum in the audio.  I can deal with that by 
> connecting a wire from the case of the computer to an alligator clip 
> which I connect to the coax input to the cable box.  Then the clip 
> comes off or I bump something and that annoying hum is back.
>