Jump to content


Ground Loop problems (plus EMI/RFI noise) when using analog composite video

3 replies to this topic




  • 852 posts

Posted Sat Feb 9, 2019 2:58 AM

Ground Loop problems (plus EMI/RFI noise) when using analog composite video outputs and audio outputs


Back in December of 2017 and in August of 2018 I mentioned that both my original 1983 Coleco ADAM computer and my used Commodore 128 computer that I recently purchased, I was experiencing a faint scrolling horizontal video ground loop and slight buzzing in the audio when using composite video output. I also mentioned that the RDL EZ-HK3 Audio/Video hum killer solved the problem. I also mentioned that the TI-99/4a computer and ATARI 130XE computer did not have this issue. Those that use digital video and audio over HDMI do not have this ground loop issue and its only a analog video and audio issue for some people.  


Over months of extensive testing, I have some information that is more accurate regarding the ground loop problems when using classic 80’s computers. While its true that the RDL EZ-HK3 does eliminate composite video and audio ground loops from the ADAM and Commodore 128 computers native composite video and audio output. What I discovered was that the ADAM computer and Commodore 128 were not creating these ground loops but the problem appears to be EMI/RFI noise on the ground wire from the power company.


Upon further testing I discovered that any 70’s, 80’s, or 90’s computer that had a two prong power supply, never had the composite video and audio ground loop problem. However every computer with native composite video output that has a 3 prong power supply is when I would always experience ground loop problems in the composite video and audio output (Hooking up the RDL EZ-HK3 would solve the issue when using a 3 prong power supplies). For example, the ATARI 130XE computer comes with a native 2 prong power supply and the composite video and audio output is perfect. When connecting a BETA third party ATARI 130XE USB power supply that is 2 prong the same awesome picture and sound from composite video output. However when connecting a third party high-end 3 prong ATARI 130XE power supply I get horizontal video hum bars with audio buzzing. Since the ADAM computer, Commodore 128, and Commodore Amiga all have a native OEM 3 prong power supply I get horizontal video hum bars and audio buzzing on those computers. To try an eliminate the ground loop problem I literally tried almost every electrical outlet in the building by running an extension cord to other rooms to see if the ground loop could be eliminated, since the ground loop was occurring when the computer power supply is plugged in the exact same electrical outlet as the TV.  I was hoping a different electrical outlet would fix the problem. It did not matter what electrical outlet was used, same video and audio ground loop issue. To make matters worse there appears to be some type of EMI/RFI noise coming from the main power grid that even high-end $600+ line conditioners cannot filter out. It even looks like some type of signal from the power grid but I would need to have an oscilloscope to see what is going on. In some areas of the country, some power companies appear to have a lot of EMI/RFI noise on the incoming ground wire to all electrical outlets.


Since the source of the ground loop issue is electrical, I tried many ground loop eliminators and isolation transformers and none of them worked in my situation. With a 3 prong power supply connected I tried two different Hum X products for $79 each, and both of them did nothing for me to eliminate the ground loop problem. The reason I tried a second one, is in case the first one was defective. For around $200 I tried the 1000 watt UMI Toroidal Isolation Transformer and I still had the same video hum bars and audio buzzing. Just recently I tried the high-end around $450 1000W Hospital/industrial grade Tripp Lite IS1000HG Isolation Transformer with Faraday Shielding (excellent build quality). Once again the EMI/RFI noise and ground loop issue was not fixed. All of those products are being returned because in my situation they did not work to eliminate the ground loop issue. To my surprise the only way to not see and hear ground loops in the composite video and audio signal was to use a cheap $1.49 UL listed 3 prong to 2 prong ground lift adapter. That is not the ideal way to not see or hear ground loops since it is not fixing the problem, but instead is bypassing the ground plug and only using 2 prongs. However the $450 ground loop Isolation transformers with Faraday shielding dId not work for my situation. At least the $1.49 UL listed 3 to 2 prong ground lift is a work around. Yes the RDL EZ-HK3 audio/video hum killer does work but that is not fixing the ground loop problem at the electrical source and instead is fixing the issue after the ground loop occurs in the video and audio output. Ground loops are very hard to isolate and fix sometimes, and they only occur when I use 3 prong power supplies instead of using 2 prong power supplies. Therefore since every electrical outlet in the building is experiencing the ground loop issues. In my situation the work around is to use either a $1.49 UL listed 3 to 2 prong ground lift adapter or to use that RDL EZ-HK3 audio/video hum eliminator on the ADAM, Commodore 128, and Commodore Amiga’s analog video and audio output.       

Attached Thumbnails

  • 3 prong view 1.JPG
  • 3 prong view 2.JPG

Edited by HDTV1080P, Sat Feb 9, 2019 3:27 AM.

#2 SiLic0ne t0aD ONLINE  

SiLic0ne t0aD

    River Patroller

  • 2,398 posts
  • Rock 'N Roller, Space Patroller
  • Location:Ohio Valley

Posted Thu Feb 14, 2019 4:44 PM

I use those adapters a lot in my house, since it has antiquated wiring w/ grounding problems ... Something I hope to start upgrading. I need to get more of these adapters until then though. :)

#3 -^CrožBow^- ONLINE  



  • 6,874 posts
  • Collector of Fine Atari and Sega Antiquities!
  • Location:Ivory Tower, Fantasia (Oklahoma)

Posted Thu Feb 14, 2019 4:48 PM

A bunch of the outlets in my house were only 2 prong as well. Imagine my surprise when I opened them up and found solid copper grounds screwed to terminals inside the j-boxes? And in most cases, there was enough of that wire to leave it attached on that screw inside the box and still attach it to the screw terminal on a new 3-prong outlet. 


Made me wonder what the point was in installing 2-prong outlets when the house even though it was build in '65 was done so with grounding throughout in mind properly?




  • Topic Starter
  • 852 posts

Posted Thu Feb 14, 2019 6:03 PM

It is a safety issue not having the ground connected on a piece of equipment that uses all 3 prongs. That is why most of the time I plan on using the RDL EZ-HK3 Audio/Video hum killer that removes the hum bars and buzzing sound over the RCA composite video/audio connection. Then I can use all 3 prongs on the ADAM power supply and Commodore 128 power supply with out the grounding loop problem.

Edited by HDTV1080P, Thu Feb 14, 2019 6:06 PM.

0 user(s) are browsing this forum

0 members, 0 guests, 0 anonymous users