Hum/buzz on OBi202

[chris56]

I've owned an OBi202 for over a year now and haven't had any problems with it. It works great.

Recently, I purchased another OBi202 on Amazon to add to my network.

However, I've been having issues. I went through a great deal of troubleshooting (steps taken detailed below), and when all of that failed, I exchanged the unit for another only to have the same problem. I am beginning to wonder if there is a bad batch of OBi devices in circulation.

The problem: there is a hum/buzz heard over the phone when the line is quiet.

Here are the steps I've taken to troubleshoot the problem:

- Swapped power supplies (took the PS from the good unit and tried it on the new ones)
- Connected the units to different wall outlets
- Connected the units with and without a surge protector
- Tried different phones
- Peformed a factory reset


Additional Information:

- Telephones tried are the corded type
- Hum/buzz occurs regardless of the telephone used
- The hum/buzz goes away completely when the phone's mute function is engaged
- Unit hums/buzzes regardless if connected to a router/network
- All units have/had the most up-to-date firmware

I've ordered a linear regulated power supply to see if that helps any. I've read on here that it solved another user's hum problem. I really don't know what else to try. The only thing I can think of is that there is a bad batch of units.

[SteveInWA]

The obvious question is:  did you contact Obihai about this?  The units are under warranty, after all.

[chris56]

I didn't contact Obihai about it because I wasn't sure if the problem was with the unit(s) or something else.

I did some more troubleshooting tonight. I am getting somewhere...

I connected the problem unit to a 12V car battery and the line was dead quiet! I also connected it to the 12V output of a computer power supply. Again, the line was quiet. So it's definitely a power supply issue. But what baffles me is why there is still noise when I connect the power supply of the OBi202 that I purchased last year. That unit is dead quiet when using that power supply. Doesn't make sense to me.

Oh, and I also tried a power supply from an old Netgear router and that resulted in the buzz/hum.

[SteveInWA]

Do you realize that lead-acid car batteries supply 12.6VDC when disconnected from the car, or 13.7VDC to 14.7VDC when connected to a running car, at enough current to make your OBi explode if it was defective, and there wasn't a fuse in the circuit?  At least it didn't fry your OBi.

If the old OBi doesn't cause hum, and the new one(s) do, then contact Obihai.

Have you tried using a telephone which doesn't have its own AC/DC power supply?  In other words, a bare-bones, single-line, wired telephone?  It sounds like you have a ground loop between the phone and the OBi.  There are filters available to block this, but you should try to identify the underlying cause.  If you can take the OBi and a basic telephone to another building, it would be worth testing it that way, too.

[AirMel]

I plugged a USB cable into the Obi and used an alligator clip from the shield of the USB cable to a ground on my mixer (any 'real' ground will do) and the vast majority of the hum/buzz is gone.

[PeterOBIone]

Did anybody had a solution for this? I have the same problem with a OBI202 I bought in August 2021.
I don't want to have to fiddle with cables and alligator clips. The unit should work out of the box, right?