Mains interference on landline phone

Stoodles

There is a buzz on my landline and unplugging it from the mains supply stops the buzz. It is definitely not related to the Broadband hub: it makes no difference whether that is that is plugged in/switched on or not.



I have tried it on different mains socket circuits around the house, and it persists on all three. My next step will be to try switching off appliances in turn to see if one of them is interfering. I suppose I also need to try turning off the lighting circuits etc at the fuseboard.


Is there a filter I can buy to cut out this interference?



.

arciere

Stoodles wrote: »

Is there a filter I can buy to cut out this interference?

I don't think there is, you have already checked the ADSL line so it looks like it's not coming from there.
When you say that the interference stops when you unplug (it) from the mains, what are you referring to?

Stoodles

I'm not sure what you are asking. The buzz stops when I unplug the phone from the mains - that is why I assume it is a mains interference problem..

arciere

Stoodles wrote: »

I'm not sure what you are asking. The buzz stops when I unplug the phone from the mains - that is why I assume it is a mains interference problem..

Yeah, but it can also be the phone that is faulty. Also, if it's a telephone that requires power, how can the OP know that the buzz is gone if the telephone is unplugged?

System

If it is a phone that is plugged into a power supply then the problem is the PSU is faulty. There is absolutely no way at all the noise is coming from the phone line. Phone line is AC but its on a 50Hz frequency which is inaudible. On the other hand the PSU is a switch mode supply which switches thousands of times a second which is audible.

If it was an ADSL signal then that would be a hiss, not a buzz.

Stoodles

arciere wrote: »

, how can the OP know that the buzz is gone if the telephone is unplugged?

The phone line still works when the phone is unplugged, so I can unplug it, hear that the buzz is gone, the plug it back in and hear it restart.

Stoodles

Tarambor wrote: »

the PSU is faulty.

I'm afraid I don't know what PSU stands for, or what I can do about it. My understanding stops at school physics - electricity creates a magnetic field, and speakers work with magnets, so one is affecting the other.

DoaM

What model phone are you using? If it's a cordless handset, which base unit are you unplugging from the mains? (The main unit which plugs into the phone socket, or the power base for an additional handset)?

Unless we know the phone model and your setup it's near impossible to advise properly. All the indications are that it is a problem with your phone (i.e. a base unit).

PSU = Power Supply Unit. In this case they take the 230V AC mains supply and convert it to a DC supply for the phone etc. This type of PSU uses a switched mode power supply running at a frequency that would be audible as a buzz if there was a fault. (50 Hz mains would be a very low hum).

Stoodles

It's a Binatone 3525, with a corded base unit and a cordless second handset. Unplugging the base unit stops the buzz.


I'm not sure of the difference between a buzz and a hum - can you give some examples?

dggar

Tarambor wrote: »

If it is a phone that is plugged into a power supply then the problem is the PSU is faulty. There is absolutely no way at all the noise is coming from the phone line. Phone line is AC but its on a 50Hz frequency which is inaudible. On the other hand the PSU is a switch mode supply which switches thousands of times a second which is audible.

If it was an ADSL signal then that would be a hiss, not a buzz.

That is approximately the frequency of the lowest G note on my piano. I have no problem hearing that.

DoaM

Stoodles wrote: »

It's a Binatone 3525, with a corded base unit and a cordless second handset. Unplugging the base unit stops the buzz.

Probably because you've stopped all landline telephone communications. (The remote handset won't be able to make a call if the base unit is powered off).

Stoodles wrote: »

I'm not sure of the difference between a buzz and a hum - can you give some examples?

https://www.youtube.com/watch?v=J8op6HpvweM ... that's a hum. What are you meaning by a "buzz"?

To my mind your base unit has a power supply fault.