# AC hum on phone



## LARMGUY

480sparky said:


> Anyone have a source for a filter to remove AC hum from a phone line? I got a customer with a bad case of 60 Htz noise on one phone, and even the supply houses look at me strange.
> 
> I *don't* need a DSL or RF filter.


 
Assuming you have already tried the RF filters it sounds like a bad splice or connection on the phone line. Also assuming with the A/C power off it goes away? It could also be induced by any equipment attached to the phone lines like an alarm panel. If it is not equipment related, I would call the phone company.


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## TOOL_5150

Have you pulled everything off the MPOE and checked hum there? If there is hum at the MPOE with no house lines connected - its the phone companies issue.


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## RIVETER

Try a different phone in the location.


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## TOOL_5150

RIVETER said:


> Try a different phone in the location.


Not trying to crap on your post, but It usually doesn't have anything to do with the phone itself. Its usually interference or a shorted pair:thumbsup:


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## RIVETER

TOOL_5150 said:


> Not trying to crap on your post, but It usually doesn't have anything to do with the phone itself. Its usually interference or a shorted pair:thumbsup:


My posts can usually take a lot of crap, but thanks for the apology. Those who know AC rectification and subsequent filtering of the DC are familiar with HUM if the filtering is not just right. That filtering could be eliminated by employing a different usage device. That is all that I am saying.


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## 480sparky

I pull the runs off the lines coming in at the demarc. The hum remains on the house side. It's 60-cycle, the same I hear on my fox & hound when it's near an AC line.


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## RIVETER

480sparky said:


> I pull the runs off the lines coming in at the demarc. The hum remains on the house side. It's 60-cycle, the same I hear on my fox & hound when it's near an AC line.


Have they/you checked with the phone company? It would seem to be their responsibility.


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## 480sparky

RIVETER said:


> Have they/you checked with the phone company? It would seem to be their responsibility.



No. The hum is present on the house side when it's disconnected.


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## RIVETER

480sparky said:


> No. The hum is present on the house side when it's disconnected.


Okay...how could that be? Some external equipment could be the culprit. Usually, it is not cost effective to hire an electrician to figure it out. Are you a relative?


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## 480sparky

RIVETER said:


> Okay...how could that be? Some external equipment could be the culprit. Usually, it is not cost effective to hire an electrician to figure it out. Are you a relative?



No.... this is an ongoing job. Kitchen remodel. There's a 60-cycle hum throughout the house on all the phone jacks. I disconnect the entire house at the demarc, and the hum persists. HO is only complaining about the one jack they're using for a cordless phone. Unplugging it makes no difference... I get the same hum I hear on my fox & hound no matter where I clip my test set into.

I remember filters for this being sold at Walgreens fer cryin out loud. These days, no one knows what they are, let alone where to get them. Somewhere in the house the phone lines are picking up AC, and being an existing house it would be he11 to t-shoot it. I'm thinking a simple $3 filter would be far quicker. Apparently, I'm the only one who remembers them, JFK and the Gemini program.


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## RePhase277

A couple questions:

1) what kind of wire is ran to the phone jacks?
2) When disconnected from the demarc, and no phones connected inside, do any of the wires have continuity to ground?

Several turns of wire on a toroid going in opposite directions for tip and ring at each jack may cancel the hum.

Also, if you like making circuits, there are a few simple 60 Hz "notch filter" circuits that are easy to build.


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## 76nemo

Can't say as I have ever seen them at Walgreens:no:, but I think what you're remembering is what were called SNIX, (Signal Noise Interference Xterminators) boxes or filters Ken. All they are is a simple attenuator.

http://www.sncmfg.com/telecom/noise_protection/snix.html


If you're talking of anything else, I don't have a clue. In the age of twisted pairs, those filters are pretty well _filtered _out.


Let us know how ya' make out. Good luck Ken.


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## MDShunk

Ken, Mike Sandman used to sell those. Probably still does. I remember watching him talk about eliminating 60cy hum on one of his old VHS tapes.


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## cdnelectrician

It would seem there is more to this than just installing a filter, there is a problem that should probably be fixed elsewhere in the house...Did you try turning off breakers one by one while listening with your test set? How are the jacks wired, daisy chained or home runs?


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## 76nemo

cdnelectrician said:


> It would seem there is more to this than just installing a filter, there is a problem that should probably be fixed elsewhere in the house...Did you try turning off breakers one by one while listening with your test set? How are the jacks wired, daisy chained or home runs?


 
Not for the money and labor it's not. You see how they work?


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## 480sparky

MDShunk said:


> Ken, Mike Sandman used to sell those. Probably still does. I remember watching him talk about eliminating 60cy hum on one of his old VHS tapes.



I checked his website. Couldn't find anything.


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## erics37

Is it just hum or is there some crackling too?


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## crazyboy

Since the hum remains when the telco is disconnected,I would try to see which one of the cables leaving the NID is causing the hum by disconnecting one at a time until it goes away. Then probably run a new one if possible.


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## 480sparky

No crackling.

Running new lines will be impossible. Huge house, 99% finished.


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## 76nemo

Now I'm confused.......is this a problem that's been there all along Ken?


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## 480sparky

76nemo said:


> Now I'm confused.......is this a problem that's been there all along Ken?



I have no clue. They're just complaining about it to me. All I did was remove the phone jack for the remodel, then install a new one after the cabinets went up.


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## 76nemo

480sparky said:


> I have no clue. They're just complaining about it to me. All I did was remove the phone jack for the remodel, then install a new one after the cabinets went up.


 

Did you bother to ask Hal(hbiss) about those filters? I skipped through most of the thread and just hit on those filters when I first saw you asked about them. You have hum with everything disconnected Has the house been resided? Sorry to pound you with questions, but it's not the HO's problem if everything rings out at the demarc entry.


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## 480sparky

76nemo said:


> Do you have a cable tester you could plug in at the demarc?
> 
> Did you bother to ask Hal(hbiss) about those filters? I skipped through most of the thread and just hit on those filters when I first saw you asked about them. You have hum with everything disconnected Has the house been resided? Sorry to pound you with questions, but it's not the HO's problem if everything rings out at the demarc entry.



Disconnect the house wiring from the demarc, hum persists. Original siding... house is only 10-12 years old.


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## 76nemo

480sparky said:


> Disconnect the house wiring from the demarc, hum persists. Original siding... house is only 10-12 years old.


 

...............................


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## 480sparky

*Problem solved!*

I TS'd it yesterday, and found that whenever I unplugged the HO's phone (although they have jacks all over the house, they only use one cordless), the hum disappeared. I was ready to tell them it was their phone causing the problem.

As I was reinstalling the jack, I happened to look straight in to the jack itself and noticed one pin was crooked. So I hooked up my test set and stuck the end of my volt sensor into it. Sure enough.... I immediately picked up the hum. I've never seen a phone line have a 60-Hz hum when the pin for the black is crossed over and touching the next pin in the jack when a cord is plugged in.

So I got out my teeny-tiny needle nose, bent the pin back into place, and all is now swell in the world.


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## sarness

It most likely is picking up the 60hz from the unused pair.


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## 76nemo

Twasn't it you that said you unhooked everything at the NID and the hum persisted?


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## 480sparky

76nemo said:


> Twasn't it you that said you unhooked everything at the NID and the hum persisted?



Yes.... because it was caused by a bent pin in a jack in the house.


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## Electric_Light

I don't really get why that would do that. If it was touching the unused outer pin(s) I can't see why it would affect it since unless they have a second line, the second pair wouldn't be hooked up to begin with


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## sarness

In older buildings most locations had 25 pair cables, 9/10 times they would be fine, everytime else you would have hum. Shorting out all the unused pairs would eliminate the hum.

Having a pin crossed over to an unused pair, especially one wire of a pair is especially prone to hum.

Home phones being analog pick up on it very easily


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## Electric_Light

sarness said:


> In older buildings most locations had 25 pair cables, 9/10 times they would be fine, everytime else you would have hum. Shorting out all the unused pairs would eliminate the hum.
> 
> Having a pin crossed over to an unused pair, especially one wire of a pair is especially prone to hum.
> 
> Home phones being analog pick up on it very easily


I have a problem with hearing radio station coming into my phone line. I might try just that to see if it would mitigate the problem.


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## 480sparky

Electric_Light said:


> I have a problem with hearing radio station coming into my phone line. I might try just that to see if it would mitigate the problem.



RF filters are fairly common.


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## Electric_Light

480sparky said:


> RF filters are fairly common.


Would that mess with my DSL?


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## 480sparky

Electric_Light said:


> Would that mess with my DSL?



It shouldn't. But I've never had to put an rf filter on a phone system that has DSL. Last time I dealt with an rf filter it was 15 years ago.


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## RePhase277

I would just guess that the short to the other pin changed the capacitance of the active pair and threw it out of balance, allowing the 60 Hz hum to bleed in.


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## erics37

480sparky said:


> It shouldn't. But I've never had to put an rf filter on a phone system that has DSL. Last time I dealt with an rf filter it was 15 years ago.


I can just imagine every jack having an RF filter plugged into a DSL filter plugged into the wall


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## sarness

erics37 said:


> I can just imagine every jack having an RF filter plugged into a DSL filter plugged into the wall


I usually install the filter at the demark and run a dedicated pair to the modem.

Same with any type of filter, best installed on the incoming line.


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