Utilizing a Telos 1x6. I have used a lot of these systems in the past, but never really encountered the hum problem I have with one particular system, and facility. The hum isn't bad, but I'd like to eliminate it, or lower it if I can. The hum is on all of the phone company delivered analog phone lines. What I've discovered with this system is that phone line polarity makes a difference. I now have the lines at their lowest hum level (flipping polarity on each line and listening to it). 6 lines going in to the 1x6. One is from the in-house PBX (I'm not really concerned with that one). Is there an isolation transformer out there that is made specifically for this application, and passes ring voltage and everything else that is needed to make the Telos system work?
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Phone line hum
- Thread starter Brian Bowers
- Start date
If you've identified the (ground loop) hum is mainly coming from your Telos, have you tried lifting the AC ground on the 1X6? I've used one of those ground lifts you can buy at the hardware store. By your description, it sounds like a classic case of your phone line ground and your 1X6 ground being different.
I've thought of it, but I haven't tried it yet (didn't have ground lifter adapter handy). As simple as they are, I sometimes rely on those 3rd prong ground connections for lightning protection, especially with a box that deals with phone lines (even though I have phone line lightning protection even prior to that box). Plus, I don't think the NEC recommends lifting the 3rd prong ground. Even though I have used ferrite before in many applications, I have just read that it is recommended that in a phone line application, to take the tip and wind it in one direction around the toroid, and take the ring, and wind it in the other direction. I think I'll give that a try.
You might try lifting one end of the shields on the send and receive audio pairs. I'd disconnect the shields at the Telos end.
Low level (pretty gosh darn low) hum (sounds like 60 Hz) is only present when lines are punched up. Hum level varies from line to line (one line is the quietest of the 5). I didn't think of lifting audio shields for ins or outs to the Telos, as when I have the fader up, with no lines punched up, there is absolutely no hum. I'd swear the hum is on the lines themselves. Of course, listening on a butt set, you wouldn't hear this low level of hum, but when the lines are on the air, you can hear it. We've had two different 1 x 6 sets in this studio, and they both exhibit the same exact amount of hum.
Of course, the problem might be with the phone lines themselves. They should be balanced. If the hum level changes when you punch up different phone lines, the lines are not balanced.
Call the telco and ask them to test the lines. Keep on them until they understand that you will not just "go away."
Call the telco and ask them to test the lines. Keep on them until they understand that you will not just "go away."
>>>Call the telco and ask them to test the lines.<<<
I've tried this a number of times before with little success. I've dealt with many phone techs over the decades, but I'm not sure what to tell these guys anymore, as they keep saying everything is fine. I'm not sure they know what the word balanced means. I'm not sure I do either, in a telco world. Balanced audio? Yes I completely understand that.
I've tried this a number of times before with little success. I've dealt with many phone techs over the decades, but I'm not sure what to tell these guys anymore, as they keep saying everything is fine. I'm not sure they know what the word balanced means. I'm not sure I do either, in a telco world. Balanced audio? Yes I completely understand that.
Have you been in contact with the people at Telos? They may be able to give you some further information.
The telco must meet certain quality standards. Have the phone guys been to your site to measure the balance of the phone pairs?
That's the only way that they can determine whether a problem exists.
If you are getting hum ... and the hum is different on each line, your phone lines are not balanced.
The telco must meet certain quality standards. Have the phone guys been to your site to measure the balance of the phone pairs?
That's the only way that they can determine whether a problem exists.
If you are getting hum ... and the hum is different on each line, your phone lines are not balanced.
Well, I suppose I could give that another shot. Just so you know, a lot of the TDS techs in our area are in their 30's, and I'm not sure they're familiar with some of the older POTS technology and standards.
It's a legal issue. The telco is required (by law) to meet quality standards.
Keep complaining. Take your complaints to the very top if necessary.
Remember .... "the squeaky wheel ........"
Keep complaining. Take your complaints to the very top if necessary.
Remember .... "the squeaky wheel ........"
As much as I appreciate the pep talk, and the info, I'm wondering if we're already meeting *their* quality standards. I mean, how is one really to know for sure? I sure don't have any of the necessary test equipment that the techs have to confirm anything. Is there a S/N ratio that POTS lines are required to meet? If so, does anyone pay any attention to it anymore? I'm willing to bet money that if I ask the tech to balance the lines, he's going to look at me with a confused look, while asking, "what do you mean balance the lines?" I'll give Telos a call too.
Do call Telos and ask them to explain the meaning of "balanced" as it applies to telco POTS circuits.
OK, did a little Google research (while waiting for Telos to call). One of the more popular pieces of test equipment for POTS lines was the Wilcom T136B. There are currently a number of them on ebay. One of the functions of this piece of test equipment is Noise. This is what I found on the internet regarding POTS line noise:
NOISE
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1) Objective is 20 dBrnc or less. Readings between 21 & 30 dBrnc are
marginal, the service will work but resolution action must be scheduled
to achieve objective.
a) Measure with a Wilcom 136B test set (or equivalent).
Regarding balance:
BALANCE
-------
1) Objective is 60 dB or more.
a) Balance = Power Influence minus Noise.
b) Balance under 60 is generally acceptable if BOTH noise and power
influence are in the objective range.
Prices for the Wilcom's on ebay are pretty cheap. For the heck of it, I think I'll pick one up, if not just to satisfy my own curiosity regarding my POTS line noise levels. Thanks for the advice.
NOISE
-----
1) Objective is 20 dBrnc or less. Readings between 21 & 30 dBrnc are
marginal, the service will work but resolution action must be scheduled
to achieve objective.
a) Measure with a Wilcom 136B test set (or equivalent).
Regarding balance:
BALANCE
-------
1) Objective is 60 dB or more.
a) Balance = Power Influence minus Noise.
b) Balance under 60 is generally acceptable if BOTH noise and power
influence are in the objective range.
Prices for the Wilcom's on ebay are pretty cheap. For the heck of it, I think I'll pick one up, if not just to satisfy my own curiosity regarding my POTS line noise levels. Thanks for the advice.
Truthfully, I don't think the carrier is of any significance. Quality is worsening regardless of phone types. Clicks, buzzes, hums, dead air, the underwater gurgle, and the list of deficiencies in quality could go on and on. But you will get lots and lots of explanations, complete with how it must be your problem all the way around, despite millions of other people who have problems regardless of carrier.
It's not a real solution but it might help while you're looking for the cause: Our Stereo Tool FM processor has a "PNR Noise & Hum" filter which can learn the signature of the hum and then filter it out - in case of constant tones it can filter them out completely with nearly no side effects. It's similar to filters that are present in many wave editors such as CoolEdit and Audition, but it can be used in live mode. So if you have a spare pc lying around you could use it for this. No Stereo Tool license is needed, the free version suffices.
If lightning comes down the phone lines, ground of your Telos box isn't going to save it from damage. Lift the ground with a $3.50 ground lift adaptor. My guess is your problem will be solved. Either that, or make sure the ground of your incoming phone lines is at the same ground potential as the AC ground of your Telos gear.
>>>make sure the ground of your incoming phone lines is at the same ground potential as the AC ground of your Telos gear.<<<
Great point!! I am only at that facility on a part-time basis, but that will be my first thing to try. It makes total sense. I can remember one time utilizing an AT&T Dedicated Program Audio Circuit for a live broadcast. I was in the process of connecting it to the studio, when I discovered it was plagued with AM RFI. Along with a 50K FM at this site, we also had a 1K Non-DA AM. I tried everything I could think of to get rid of the AM RFI, but none of my ferrite ideas worked. It was getting late, I was getting a headache, and as a last ditch effort, I tried connecting the AT&T copper housing of the studio located Dedicated Program Audio Circuit to the facility star ground system, and the RFI disappeared immediately. I have a feeling that this might be the solution with my phone lines, and Telos 1 x 6. Even though the facility has a halfway decent star ground system in the building, it doesn't extend into the studios. We simply use the AC conduit ground, and 3rd prong grounding of individual rack components, in the studios. No one ever installed dedicated grounded outlets in the studios. I know for a fact (as I did it) that the phone carrier demarc ground is connected to the building star ground system. It now concerns me that studio gear may not be at the same ground potential as the star ground system is at. I will definitely be researching that in the future.
Great point!! I am only at that facility on a part-time basis, but that will be my first thing to try. It makes total sense. I can remember one time utilizing an AT&T Dedicated Program Audio Circuit for a live broadcast. I was in the process of connecting it to the studio, when I discovered it was plagued with AM RFI. Along with a 50K FM at this site, we also had a 1K Non-DA AM. I tried everything I could think of to get rid of the AM RFI, but none of my ferrite ideas worked. It was getting late, I was getting a headache, and as a last ditch effort, I tried connecting the AT&T copper housing of the studio located Dedicated Program Audio Circuit to the facility star ground system, and the RFI disappeared immediately. I have a feeling that this might be the solution with my phone lines, and Telos 1 x 6. Even though the facility has a halfway decent star ground system in the building, it doesn't extend into the studios. We simply use the AC conduit ground, and 3rd prong grounding of individual rack components, in the studios. No one ever installed dedicated grounded outlets in the studios. I know for a fact (as I did it) that the phone carrier demarc ground is connected to the building star ground system. It now concerns me that studio gear may not be at the same ground potential as the star ground system is at. I will definitely be researching that in the future.
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