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Intermittent mains hum is driving me nuts - Page 2

post #16 of 26
1/26/10 at 11:11pm
Has anyone mentioned fluorescent lights yet? They can throw off a bit of RFI (radio frequency interference) that can show up as a hum. Hasn't the EU dumped incandescent bulbs? There's a chance that the fluorescents might be responsible. LED lighting would be better than a CF.

Isolation transformers absolutely will take the DC off your line. They're not terribly expensive - I use one that I originally bought to keep from frying myself with old tube radios. It cleans up the line well and it was about $30 USD.
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post #17 of 26
1/27/10 at 9:29am
Thread Starter 
I agree that fluorescent lights are a source of interference. This is clearly demonstrated with my mains-connected radio in a poor signal area (reception on the limit of hiss being a problem). If I connect a low energy table lamp to a socket anywhere near the radio's socket, then I get the most terrible noise coming out of the radio. No it's not Mariah Carey, it's just a terrible noise! Same thing when I plug in my laptop. But neither of these are the cause of "the buzz".

This is what I'm going to do: Wait until the next "buzz moment", then measure for DC voltage whilst gradually switching off all my ring mains circuits at the junction box. Also measure the DC when there's no buzz. This should isolate whether DC Voltage is the issue and whether the problem originates from any part of my house. Due to Murphy's Law, this may take some time...
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post #18 of 26
1/27/10 at 5:30pm
To oversimplify a bit, but still be technically accurate, there are two possible kinds of things going on in your situation:

1. noise on the power lines, which would cause edgy sound, or noises coming from your speakers/headphones

2. dc on the powerline, and/or asymmetrical, i.e., distorted ac waveform.

both can be investigated by unplugging electrical gizmos and seeing if one is the culprit. in most electrical grids, it can be something outside the house, making it harder to pinpoint.

if it is 1, then filters can help

if it is 2, then you would hear the components actually vibrating, especially if they have torioidal transformers in them, as toroids really don't like dc or distorted waveforms. this can be a problem caused by bad transformers used by the power delivery company.

hope this helps focus the troubleshooting a bit.
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post #19 of 26
1/28/10 at 3:23pm
Thread Starter 
Thanks fzman and everyone. Well, I managed to measure the DC voltage during and after "the buzz". In both cases, it randomly fluctuated within the +/- 0.3v range, very occasionally peaking to +/- 0.6v. So that looks to me as just low level random noise and therefore DC voltage is not the problem.

It wasn't practical to start isolating different circuits, so Sherlock will have to continue the investigation the next time.
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post #20 of 26
1/28/10 at 4:38pm
Couple of questions.

What kind of plugs do you have? Please reference the wikipedia article if you can. Are the plugs for all three devices correctly polarized, or can any be plugged in multiple ways?

Is the television connected to anything else? Is that anything else also connected to the same filtered power strip? Is there a cable (for cable tv, satellite, or antenna)? If so, disconnect anything else connected to these cables and report.

There might be reasons why these particular components are the ones affected. Plasma TVs are naturally susceptible to buzz, not just in the transformer. Same with microwaves. The clock radio's probably just cheaply made to a low electrical standard, so the transformer could be physically loose or another part might have gone out of spec, or it could be manufactured that poorly. All of these devices can deteriorate in time and start having these problems later.

Obviously the problem is something that gets into the house wiring or generates a magnetic field. Given the devices that are affected, the wiring seems more likely. That's the reason for looking for hidden electrical paths.
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post #21 of 26
1/28/10 at 8:30pm
You have stated that it is recently more apparent, has it corresponded to colder temperatures?
Wondering if it could be noise from your heating pump?
It could also be someone in the neighborhood who has started to use a new electronic device...arc welder, sodium vapor or mercury halide lights,or???.
Might also be the transformer on your lines starting to age
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post #22 of 26
1/29/10 at 1:29pm
Thread Starter 
SiBurning, the TV shares the same filtered Belkin strip as the rest of the AV stuff: DVD, small AV amp and PVR. If buzzes even if these are not active (i.e. in standby), but I will check further.

883dave, it’s definitely not the heating pump, but I’m coming round to the idea that it may be a neighbour (as others have also suggested). It appeals to my fundamental sense of fairness: always blame someone else

No buzz last night – and the neighbour under suspicion was out. This level of investigation may get me into trouble. Picture this scene on Friday night: My wife and I are drinking a bottle of wine and watching TV. The buzz starts and I instantly leap into action, spilling the red wine all over my wife’s new dress. Undeterred, I rush to the junction box to disable various circuits whilst telling my wife to stand by the TV and listen for the buzz. This proves nothing, but my wife has now blown a fuse. So I rush out and knock on my neighbour’s front door. I’m somewhat taken aback when she appears in a nightie. I ask her if she has switched on any appliances in the last 5 minutes, but the words come out wrong and she slaps me in the face and slams the door. So I stagger back to my house which is now plunged in darkness because I messed up the junction box. That’s when the police arrive…

I promise I have not started drinking early.
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post #23 of 26
2/1/10 at 11:09am
Thread Starter 
A quick update and possibly final conclusion:

By disconnecting various circuits and appliances, I've now totally discounted ALL the appliances and circuits in my house. I even isolated the 3 appliances individually - e.g. disconnected the TV and the buzz continued on the other two.

From monitoring, at a respectful distance, the local comings and goings, I'm now also fairly sure that the culprit is one of my neighbours. Sadly, not the lady in the nightie, but another neighbour who can be incredibly defensive - so I'm working out my most diplomatic opening gambit before tackling that one.
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post #24 of 26
2/1/10 at 11:58am
Quote:
Originally Posted by TheAttorney View Post
A quick update and possibly final conclusion:

By disconnecting various circuits and appliances, I've now totally discounted ALL the appliances and circuits in my house. I even isolated the 3 appliances individually - e.g. disconnected the TV and the buzz continued on the other two.

From monitoring, at a respectful distance, the local comings and goings, I'm now also fairly sure that the culprit is one of my neighbours. Sadly, not the lady in the nightie, but another neighbour who can be incredibly defensive - so I'm working out my most diplomatic opening gambit before tackling that one.
And you are positive it is nothing to do with your heating system? I.E. the noise exists when you are positive the heating system is not powered in any way.

Reason I say this is the only way the noise could influence your devices is via excessive line noise and most likely not radiated since you neighbor is a good distance and unless he has a high powered radio transmitter most likely does not have anything of enough power. Line noise should be easily taken care of with the PSU in your devices sure some may not handle it well but the fact that 3 do not handle it makes me wonder. If it is line noise have you tried using a line conditioner, you can buy one and see if it fixes it if not return it.

If it is your neighbor what do you expect him to do? He is not going to replace whatever is causing the issue even if he could identify what is causing it.

Another ? for you, is there anything nearby that would generate large amounts of radiated energy? Think of things like TV/Radio stations, or military bases, airports, etc.
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post #25 of 26
2/1/10 at 4:50pm
Thread Starter 
m1abrams, I switched off the ring circuit (containing the heating equipment) by switching off the circuit breaker at the main junction box - so that should totally take that circuit out of action. I've used 2 power conditioners as in earlier posts, but these just deal with higher frequencies - they wouldn't correct distorted waveforms of the type fzman mentioned.

I'm not expecting my neighbour to replace anything necessarily - in the first instance just identifying the root cause will be a step forward. He does however have his house up for sale at the moment, so if I wait long enough...

There are no radio transmitters etc nearby. The closest thing of that nature is a military airport (Fairford, home to the international air tatoo) about 20 miles away, but if that was radiating something significant, then there are thousands of homes which are much closer.
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post #26 of 26
2/1/10 at 4:59pm
Quote:
Originally Posted by TheAttorney View Post
There are no radio transmitters etc nearby. The closest thing of that nature is a military airport (Fairford, home to the international air tatoo) about 20 miles away, but if that was radiating something significant, then there are thousands of homes which are much closer.
Well actually that airport could very well be an issue depending on how you sit in the flight path. I use to live near an air base and it caused all kinds of issues with electrical gear. My keyless remotes to my cars were pretty much useless at home, had to be within about 3 feet of the car to work. Course I was a bit closer to the air base (10 miles).

Now the reason I was pushing for the heating equipment is because it produces radiate noise (not bad power, though it can cause that too), this kind of noise would not be solved by power conditioners or better power supplies.

I just do not think you would get this kind of interference from a neighbor unless they had some serious power transmitting happening, or very heavy motors. You did say this was in a detached home correct? Heck depending on how the neighborhood is wired you might even be separated by transformers with isolates your power even more. My house is this way each house has there own transformer at the street (rural area with lots of distance between homes).
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