Ground loop issue when using a UPS - Page 1
Forum section: electronics / general

author: Halcyon
author_rank: Unknown
timestamp: March 02, 2017, 11:41:37 pm
content: Someone smarter than me might be able to answer this one.I had a small APC BackUPS connected to my AV gear which I've since removed because it seems to be causing an issue with ground loops in my equipment.With the UPS connected (and all the gear connected via a power board), I get awful distortion and hum from the amp when there is no audio signal (either when the media centre is turned off or the signal cable is disconnected). Same goes if I try to use my Sega Master System, the audio and video from the analog RF out is just completely overwhelmed and unusable. I've also noticed that on the power board, the "Ground" LED is off whenever it's connect to the UPS.Remove the UPS and all the problems go away and the ground LED lights on the power board when it's connected directly to the mains socket.Is this normal design for a UPS? Does it create it's own "artificial ground" or something?

author: DimitriP
author_rank: Super Contributor
timestamp: March 02, 2017, 11:50:26 pm
content: Sounds like a mibehaving UPS.At the back it should have outputs for both backup power and surge protected only (usually with a picture of a printer".Does your system behave the same way connected to either plug ?I just checked mine and there is continuity from the power cord ground to all the outlet grounds including the grounding screw terminal.

author: Halcyon
author_rank: Unknown
timestamp: March 02, 2017, 11:53:45 pm
content: Quote from: DimitriP on March 02, 2017, 11:50:26 pmYes it does. I'll try the other socket.I really need to get a multimeter, I'm hanging out for the new EEVblog model.

author: DimitriP
author_rank: Super Contributor
timestamp: March 03, 2017, 12:04:32 am
content: Probably a broken ground connection especially since the power board doesn't "see" one.Time to take it apaaaaht!

author: Halcyon
author_rank: Unknown
timestamp: March 03, 2017, 12:07:43 am
content: Quote from: DimitriP on March 03, 2017, 12:04:32 amYes I suspect that might be the case, I'll open it up and check it out. I also wouldn't put it past the IEC C14 to "Power Outlet" type adapter either. That could be the problem but I don't have another one I can test, I'll have to order one.

author: Red Squirrel
author_rank: Super Contributor
timestamp: March 03, 2017, 12:58:41 am
content: Are you seeing this noise live, or just when you record, we always had issues with 60hz hum on our recordings at church especially with dimmed lights (dimmers are quite terrible for generating noise) and I bought an external USB sound recording device (Scarlett 2i2) that takes a proper pro audio type connector and it fixed that problem nicely.Most UPSes are just standby devices and pass the AC directly, so it's odd it would be causing any grounding issues. Though I would test the plug on the UPS side just to make sure it is indeed outputting proper ground etc and not doing any funny business.

author: Halcyon
author_rank: Unknown
timestamp: March 03, 2017, 04:55:41 am
content: Quote from: Red Squirrel on March 03, 2017, 12:58:41 amLive. I don't do any recording at all with this gear. It's definitely a ground loop issue. I also use the Scarlett 2i2 as my everyday sound card on my desktop -- Great device!Quote from: Red Squirrel on March 03, 2017, 12:58:41 amYes, mine is the line interactive type, so it only does some surge filtering, buck/boost and the inverter/battery kicks in when the mains falls outside of a set range. I'll do some troubleshooting after I buy a multimeter. I don't even have a cheap crappy one to test continuity.