Persistent hum on my connected phone

Started by Jeff205, February 22, 2011, 04:11:07 PM

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Jeff205

I have a 2-line phone and whenever I connect it to my OBi I get a persistent hum regardless of what line I am using.  As soon as I disconnect from the OBi, the humming stops.  I have tried it with all computer/printer equipment off to see if there was some interference, but the issue still persists.

Any thoughts?

OBi-Guru

Do you have another analog phone to try out with the OBi?
Also the simplest thing is to press *** and listen to the IVR, see if there is any hum?

Jeff205

I tested with another 2-line phone that is exactly the same with the same results.  It does not occur with a 1-line phone.  There is a hum within the IVR, but I do not think it's an OBi issue.

I have continued to troubleshoot and the hum also stops when I remove the landline connection while listening to the IVR.  This is the first time I have used both lines together on this 2-line phone and unfortunately it looks like there is an issue.  I know I can plug my landline into the OBi, but I wanted it to ring on my second line on the phone.

It looks like it is not an OBi issue and more of a phone issue, but if anyone has encountered this before; any advice is appreciated.

Thanks.

Jeff205

It sounds like I need to reverse the TIP and RING on my landline.  Only issue is, I'm not a telephone guy and don't exactly know how to do this.  Can I switch them in the cable I use or does it have to be done in the wall jack?

RonR

Phones are not normally polarity sensitive, so reversing the Tip/Ring connections isn't likely to change anyting.

jimates

Quote from: RonR on February 23, 2011, 12:41:33 PM
Phones are not normally polarity sensitive, so reversing the Tip/Ring connections isn't likely to change anyting.
Don't know if this relates to what you just said. I haven't had a need to play with phones in a long time but at one point this mattered: If the green and red wires were reversed you would still get a dial tone, but it would not dial. pressing the button had no effect on the tone and after it timed out the recording would come on.

MichiganTelephone

Quote from: jimates on February 23, 2011, 01:16:54 PM
Quote from: RonR on February 23, 2011, 12:41:33 PM
Phones are not normally polarity sensitive, so reversing the Tip/Ring connections isn't likely to change anyting.
Don't know if this relates to what you just said. I haven't had a need to play with phones in a long time but at one point this mattered: If the green and red wires were reversed you would still get a dial tone, but it would not dial. pressing the button had no effect on the tone and after it timed out the recording would come on.

You're both right.  Newer phones are not polarity sensitive.  And neither were most older phones, except some early models with touch tone dialing.  In those phones, the dials got their power through a single diode rectifier which would prevent power from flowing in the "wrong" direction, which would prevent damage to the touch tone pad but also prevented dialing if tip and ring were reversed.

Later on the phone manufacturers started incorporating a bridge rectifier circuit (similar to what's used in many "wall wart" power supplies to convert AC to DC) into their touch tone pads, so no matter with side of the line was + or -, the touch tone pad would always get the correct polarity voltage.  With those phones, and with newer all-electronic phones that also use bridge rectifiers in their power supplies, it should not make any difference which side is tip or ring.  A phone line is supposed to be a "balanced" connection, so reversing tip and ring should not make any difference.

What happens if you connect a phone directly to the phone line and dial a single digit to "break" dial tone? Do you still hear the hum?  What if you plug a phone into the test jack in the network interface device outside your home and do the same thing - do you hear the hum there?  If you do, there may be "Longitudinal Imbalance" on your phone line (see this technical bulletin) and that's usually something the phone company has to fix (and yes, they do need to fix it, no matter how much "repair service" says it's not their problem - tell them you'll file a PUC/PSC complaint if they don't send someone out, and do it if you need to).

You have to realize that in the United States there is a LOT of aging copper out there, going into terminal boxes with corroded connections.  Plus, in the spring of the year, you get things like spring rain coupled with the thawing of snow and ice, which can cause flooding in cable vaults and even more trouble for copper cables that in some cases are well over a half-century old.  Phone companies are reluctant to do maintenance on their old copper plant because they know its useful life is limited, and we are getting closer and closer to the "tipping point" where landlines (or at least, traditional landlines from a "baby Bell" telephone company) become a thing of the past.  So sometimes you have to twist their arms a little to get them to fix problems like this.
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ludlow1953

I have the hum too.  Tried two different phones - one without external power supply.  Both have hum on line.  On two-line phone, hum transfers to line two.  If I unplug the Obi, the hum goes away.  Line 2 comes from a Magicjack plugged into USB, which gives clean, "no hum" dial tone and connection.  Tried different phone cables between phone and Obi (2 & 4 wire) without a change.  I have to believe the hum might be generated by the power supply to the Obi, but just WAG. No house wiring involved.  Phone plugged directly into "Phone" jack on Obi.  No "Line" in use.  I have used ATAs with this phone (Vonage, phone.com, etc.) with no hum.  Obi is first device to generate hum.  Hmmm... :-\

MichiganTelephone

It's possible you got a power supply with a bad capacitor or something.  Contact Obihai support (email support@obihai.com) and see what they say.
Inactive, no longer posting or responding to messages.  Goodbye and good luck.  Some of my old Obihai-related blog posts have been moved to http://tech.iprock.com - note this in NOT my blog; I have simply given the owner permission to repost some of my old stuff.

Jeff205

Even when I break dial tone, the hum is still there, but only when 2 lines are plugged in to the phone.  My home phone service is actually VOIP provided by my cable provider, so even going to the box outside would not work (plus it's only when 2 lines are connected to the phone).  It does not matter which line I remove, the Obi or my home service, and the hum goes away.  I tried 2 and 4 wire lines as well with no success.

And do you think we both received a bad power supply?

Still can't figure this out!!!!

MichiganTelephone

Jeff205, yours is an interesting situation because you say when you remove either line, the hum goes away. That sounds less like a power supply issue and more like a poorly designed phone to me, although I hate to blame the phone because it could be something else entirely.

The thought that popped into my head when I read your last message was "ground loop."  You sometimes hear it in analog sound systems where you have two different sources on different inputs and if you plug both in you get hum out of the speakers, but not if you disconnect either one (and it's a big reason why optical cabling has become so popular).  The thing is, though, that a two line phone should not be susceptible to that — even if you had two commercial phone lines, there's no guarantee they are taking the same path through the building, or even coming from the same central office!  So if you only get the problem when both phone lines are connected, then yes, it could be a bad phone.  Would reversing the polarity of one of the two lines help?  Possibly, if the hum is additive, but then again it could make it worse.

Anyway, if you don't get the hum when the commercial line isn't connected, then it's most likely NOT a bad power supply on the OBi.  But since I'm not an OBi engineer, nor an engineer of the company that made your phone or your cable provider for that matter, there's really not much more I can say about that.
Inactive, no longer posting or responding to messages.  Goodbye and good luck.  Some of my old Obihai-related blog posts have been moved to http://tech.iprock.com - note this in NOT my blog; I have simply given the owner permission to repost some of my old stuff.

Jeff205

MichiganTelephone, I'm afraid you're right.  It may be the phone.  I actually have two models exactly the same and they both do it.  I will try the polarity fix just to see if that works...will let you know.

Jeff205

I posted this on another thread and it solved my issue, but I don't want to break anything.

I am in the US, replaced my power adapter and my hum went away.  My only concern now is will it hurt to use a different adapter.  It is Input: 120VAC 60Hz 11w Output: 12VDC 500mA.  It just the first one I put my hands on (I have several to choose from), so I mainly want to make sure I do not break anything.

BoomerForum

Hi,

I have the exact same issue with my new AT&T 2-line phone.  Did you find an answer and/or does anyone know of a good 2-line phone that works with both a POTS line and an OBI VoIP line?

Mark

Jeff205

Mark,

I went to Radio Shack and picked up a power adapter that matched the original specs and everything works well now.  No issues at all.  I'm sure I could have bought a cheaper one online, but it was the quickest fix.  On my latest Obi device, it looks like there is a filter to prevent this issue.

Good luck.

MichaelW

I just bought Obis 110 and 220, and now they are both giving a hum on a connected wired phone (haven't checked on a wireless one).

The person I call hears the hum very loudly, plus serious voice distortion and clipped words. Calls are not usable.

The 220 worked OK at first. I disconnected it and connected the 110 and the hum appeared. Now both units have it.

I can stop the hum, and stop the distortion my caller hears, but touching the metal rim around the Ethernet port on either adaptor.

Anybody have any ideas on this, please?

Shale

Pay attention to the *** suggestion above. 1: Do you hear hum then?

Connect your wired phone directly to the OBi. Do not have any house wiring connected for this test. 2: Is the hum there, or was this the way you were connected all along?

3: Are you using the same power supply in each test where you hear hum?

MichaelW

#17
Thanks, Shale.

I hear the hum pressing ***, even when the local wiring is disconnected and the wired phone is direct connected to the Obi. Hum can be removed by touching metal part of Ethernet socket.

I hear the hum with two power supplies on the 110: the one that came with it (which has a small black cylinder inline with the cable, near its termination at the Obi), and the one that came with the Obi 202 (slightly bigger, no black cylinder inline). Both give hum. I have also tried plugging these power supplies in 'upside down' ie. reverse polarity in the wall socket.

Edit: also hums using a RadioShack 3-12v 1000mA adapter set at 12v +ve tip (model number 273-1680). Again, touching metal Ethernet surround fixes it.

MichaelW

Like others before me, I have found that a wireless (Panasonic) phone connected to the Obi does not exhibit hum, or distortion for the person called. Seems like this will have to be my solution.

Shale

#19
Quote from: MichaelW on April 24, 2013, 12:33:34 PM
Like others before me, I have found that a wireless (Panasonic) phone connected to the Obi does not exhibit hum, or distortion for the person called. Seems like this will have to be my solution.

Make sure the power supply on your 2-line phone is grounded if it has a ground pin. If it does not, try turning that power supply around in its socket. Since the problem does not occur for the wireless phone I presume the problem would not happen if you used a phone that does not use external power either.

If you dial ***, hear the hum, and pull the ethernet cable temporarily, does the hum happen? I am not sure what that  would mean, but it could point toward a solution. The only other think I can think of is to use a shielded ethernet cable if your are not doing so, and to use an unshielded cable if you are now using a shielded one.