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PSU Hum leaking into Audio (Ground Loop?)

SaintApoc

May 1, 2017
15
Joined
May 1, 2017
Messages
15
I am currently working on making a portable desktop (not a laptop) and have discovered that the computer speakers I have and the controller board for the monitor I pulled from a dead laptop both run off 12v. I soldered molex connectors and cable to both and ran them off the PSU (EVGA 500w 80+) and everything works. The problem is that there is a very low unannoying hum in the PSU and when the speakers are powered by it the hum is amplified through them and that IS annoying!

I did the best I could to research the problem, and I believe it is a "Ground Loop." I am not sure how to isolate the ground from the audio so that it is not on the same ground as the PSU. I understand that getting a supply that doesn't hum, dropping from 3 prongs to 2 prongs, or using an entirely separate supply (like a 12v wall transformer) would each remove the hum. What I want to know is if there is any way to fix this on the speaker/amplifier side instead of at the psu or outlet side? Is there a way to ground the speakers without going through the supply and without having to have 2 plugs come out of my computer to the wall?
 

Bluejets

Oct 5, 2014
5,852
Joined
Oct 5, 2014
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5,852
You don't mention anything about the input. It may be that you have noise coming in there. i.e. Have you used screened cable, where does the input originate.
 

SaintApoc

May 1, 2017
15
Joined
May 1, 2017
Messages
15
You don't mention anything about the input. It may be that you have noise coming in there. i.e. Have you used screened cable, where does the input originate.

The input for the audio signal? the signal is coming from the computer's rear i/o panel. Whatever I play on the computer is what comes through the speakers. I know that the PSU is culprit because the same audio source has absolutely no hum if I connect the amp board to a wall transformer instead. My intention is to have it connect to the PSU but remedy the hum from it. Is it just not possible?
Also, neither the input, output, nor the power cable are shielded. The PSU does have screened cable right up to the connectors, however. And to update, I noticed that going from 3 prong to 2 prong did not actually solve my issue.
Thank you for the reply!
 
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SaintApoc

May 1, 2017
15
Joined
May 1, 2017
Messages
15
Well, if you know what's wrong, you won't need us I guess.
Hey, I didn't mean to come off as arrogant or something - sorry. I know the problem, I am looking for a solution - so I DO need you and I do appreciate the help!

Please post some photos.
IMG_20170911_180509-picsay.jpg IMG_20170911_180421-picsay.jpg IMG_20170911_180548-picsay.jpg
IMG_20170911_180613-picsay.jpg
I do apologize for the mess in this box - it is a WIP so I don't intend for it to look like a fire hazard when it is done. I am fully aware of how unprofessional this appears. The wall transformer produces no hum in the output, but the PSU does - so I am wondering if it is at all possible to have the PSU without the hum.

Also, just in case, I thought I should clarify that the mention of the monitor was completely extraneous - I saw I could forego the extra wall adapter both with the monitor and with the amp board (pulled from computer speakers)
 
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