Noise on the mains, cause?

Discussion in 'Electricians' Talk' started by Hans_25, Jul 6, 2021.

  1. Hans_25

    Hans_25 Screwfix Select

    OK you experienced sparkies...got any ideas on this?

    I had my hifi power amps upgraded around Xmas time, Toroidals upgraded from 500KV to 1000KV (2 mono block amps)

    When they're on, I occasionally get a buzzing from the toroidals, it might happen once or twice a day, sometimes not at all, and last from a couple to 15 minutes. I understand this is cause by DC on the mains, normally due to to asymmetry or harmonics in the L-N sine wave and thus causing
    magnetostriction in the toroidal core.

    This is now happening as the larger toroidals are more susceptible than the older smaller ones, but what puzzles me is that its only been happened in the last 2 months or so, it didn't happen from Xmas to April/May.

    I wonder if some kind of high power device has been introduced locally recently, does any one have a clue might might be causing this kind of DC on the mains? I live near a railway & station. Could it be a household appliance nearby?
     
  2. quasar9

    quasar9 Screwfix Select

    You say you live near a railway - is it in the south of England where railways use third rail 750v DC ? New line side feeder equipment perhaps? Or more likely a neighbour has fast chargers installed for EV.
     
    Hans_25 likes this.
  3. Hans_25

    Hans_25 Screwfix Select

    Yes I’m in Surrey with 3rd rail.
     
  4. Tony Goddard

    Tony Goddard Screwfix Select

    I got this problem when living in Southampton and they put new rectifiers in at Millbrook station near where I lived at the time - I'm not an expert in railway electrics, but my understanding is each substation feeds one section of third rail, and obviously not a lot is going on when a train isn't on that section, when it is a lot of current is being pulled, so that might have something to do with it?
     
    Hans_25 likes this.
  5. kitfit1

    kitfit1 Screwfix Select

    I'm a bit of a Hi-Fi anorak myself lol. For a long time where i live i suffered from buzzing as well. In the end i discovered it was down to next doors solar panels, or to be more precise the bad quality of the inverter they are using.
    The cure in my case was buying a balanced power supply. It actually not only cured the buzzing, but was more like a huge hi-fi upgrade. Wider and deeper soundstage, deeper base, more precise placement.............the list goes on and on. It's defo worth at least a look.
     
    Hans_25 likes this.
  6. quasar9

    quasar9 Screwfix Select

    Have you tried a DC blocker ? Some swear by this while others dismiss this as another Hi Fi fad. They are anywhere between £99 to £300 but you could build your own. Circuits for this are available openly and have just 6 diodes, 4 large electrolytic capacitors and a resistor.
     
  7. FlyByNight

    FlyByNight Screwfix Select

    Are you serious?
     
  8. Jim Kirk

    Jim Kirk New Member

    There is no such thing as DC on the mains - the problem is caused by AC waveform harmonics determined by additional non- sinusoidal spikes on the waveform and increase in odd numbers i.e 3rd stage or 5th stage harmonics. The worst cause used to be magnetic choke fluorescent lights and other magnetic influences.

    Now the worst cause is DC rectification and switched mode power supplies in electronic equipment which themselves superimpose a square waveform on the sinusoidal AC wave.

    The harmonics do not travel back through the distribution transformer to the HV so any dirty power supply would need to be caused by your own or another consumers equipment connected to the LV side of your supply transformer or street cable or it could be RF like the old unsuppressed electric drill interfering with the transistor radio.

    What ever the cause the solution unfortunately lies within your property or equipment
     
  9. kitfit1

    kitfit1 Screwfix Select

    Yep, so in other words, a balanced power supply between the mains and Audio equipment will sort it out.
     
    ElecCEng likes this.
  10. Hans_25

    Hans_25 Screwfix Select

    I have read about balanced power supplies being used in such cases and they don't always sort it out.

    The problem is fairly well documented, caused by asymmetry on the mains, non-sinusoidal spikes which is a kind of DC i.e. its not pure AC.

    If the problem is caused on my side of the HV, then it could be from any number of places locally not just my house. At some point I will try turning off everything in my house except the hifi circuit when the noise occurs again, that will prove if its me or someone else.
     
  11. kitfit1

    kitfit1 Screwfix Select

    That is what i had to do a few years ago now. It proved to me it didn't have anything to do with anything inside my house. It did take me some time though to suss out it was next doors solar panels.
    As far as balanced power supplies are concerned, don't even look at Audio companies like Russ Andrews. Snake oil merchants all of them, Airlink is your friend. Good quality at 1/4 of the price.
     
    BiancoTheGiraffe and Hans_25 like this.
  12. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    I agree with KitFit, do NOT go near the audiophile shops!

    It never ceases to amaze me how much they can screw out of people for utterly pointless rubbish!
     
  13. quasar9

    quasar9 Screwfix Select

    Everyone has their “poison” and I won’t judge on what they spend it on. If your ears can tell the difference and you can afford it, go for it. But having said that HI Fi has come a long way since the 70s when it started to become a mass market product driven by the Japanese big brands. Then there was Amstrad at one end and British makes like Leak, Goldman’s, Sugden (among others ) with a range of Japanese product in between. Decent speakers and turntables were invariably British. The difference in quality was audible, no,pun intended. But now the sound quality across the industry has come up, especially with speakers. The difference between top and bottom is narrow and getting narrower.
     
  14. MGW

    MGW Screwfix Select

    Many years ago I had problems, it started when new door had wall lights fitted. It could be said the lights caused the problem, but really it was poor audio system design.

    The speaker wires were acting as aerials picking up the 50 Hz. I have found this again and again, specially with cheap car radios, you can fit all the fillers, and other devices, but if the audio system is a poor design, then little you can do.

    The problem is high price does not mean high quality.
     
  15. The Happy Builder

    The Happy Builder Screwfix Select

    After working for decades in the building trades the whistling in my ears makes it a bit pointless spending huge amounts on audio equipment.

    They used to laugh at me using ear plugs under ear defenders whilst working, but it has not stopped a touch of tinnitus.
     
  16. kitfit1

    kitfit1 Screwfix Select

    Actually, consumer Hi-Fi hasn't moved at all since the 70's. Cheap rubbish then is still the same cheap rubbish now, just rapped up in a digital way instead.
    I was a teenager in the 70's when i bought my first Hi-fi................it was **** then...........and the same sort of first buy for a teenager now is still ****.
    Hi end hi-end hi-fi then was so far out of my reach, it was impossible. The same is still true now, only i'm not a teenager now, so can afford hi-end.......................and am more than happy to embrace it lol.
    As regard speakers, you could not be further from the truth. In my entire life, i have only owned 3 pairs of speakers. All of them were expensive when i bought them, the first being Ditton 15's, the second being B & W CDM1 se's, and current being Spendor A9's. Cheap speakers have always been cheap and mediocre, they still are now.
     
  17. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    Speakers are worth spending reasonable money on.

    It's the gold plated cables that amuse me (particularly when they're digital!) and the £300 mains leads!
     
    kitfit1 and MGW like this.
  18. Jim Kirk

    Jim Kirk New Member

    Not quite - DC is a straight line with no spikes - but you are right it is spikes on top of the AC waveform like white foam on top of the sea waves- this changes the frequency and superimposes RF on the AC supply.

    If you had HV in you house the sound sysytem would be the least of your worries as the house would be burnt down. What I said was your side of the LV to your house from the street - it cannot come from HV or a supply to a railway transformer as the power transformer has isolated non-contact windings.
    Yes it could be from anybody in the area using unsuppressed electrical equoipment but it would have to be faulty old or non-compliant as it would not meet modern standards.

    Breaches used to be reported to and controlled by the GPO but that is long gone - I think but I'm not sure it would be your local power company district network operator - not your energy supplier.

    Yes - turn everthing off and I mean everything off - Fridges and feezers are also cuplrits but you need to keep the house powrer on for your sound equipment.
     
  19. MGW

    MGW Screwfix Select

    Yes correct, I remember my dad had bought a audio system, spool to spool, record deck, and radio back in the late 60's when transistors were relatively new, and he thought it was bee's knees, I was learning to play the electronic organ, and would record my playing then play it back, and what I was hearing on play back did not sound anything like what I thought I had played.

    I was recording direct so not the microphones, then I realised I could actually play it back through the organs speakers, and then it did sound like what I thought it should sound like, so next was play the record of Liverpool cathedral organ through the organs speakers, oh what a difference, dad opened the speaker boxes and they were empty voids, re-boxing them did improve them, although not as good as the organs speakers.

    However even back then picking up RF was a problem, two Police houses across the road, and when the Police car radio was used, it came through the organs speakers.

    I have seen this many times since, with CB specially as tended to not be made as well as amateur radios, and radios can cause a problem just because a bolt is rusty in the tower and acting as a diode.

    I remember what we called fox hunting, one guy would go out with a radio and hide, and as a club we had to find him, he would transmit for set time per minute, on one event he hid under the power cables, his signal seemed to come from everywhere, the fox got away that day.

    But the filters should be part of the audio equipment, easy enough to make band pass filters so the audio equipment should simply not receive and amply the mains born signals, but some times you find people intentionally generating mains born interference, this sort of thing [​IMG]which really should be banned, but seems very popular so modern equipment has to be designed to reject those signals.
     
  20. kitfit1

    kitfit1 Screwfix Select

    Gold plated connectors are fairly much standard really. Because they don't corrode and tend not to interfere with the signal, even with digital interconnects. Gold plated cables though are pure "snake oil" rubbish on digital interconnects lol.
    As for £300..................to a £1000+ mains leads............................snake oil at it's most greedy :D
    The only thing that matters in hi-fi mains leads is that they a fully shielded. Most actually are not, so buying a decent mains lead is defo a benefit. Maybe £30 or £50 will get you to that point.........................anything more expensive means more money than sense, or you have taken that snake oil in 100% :D
     
    Last edited: Jul 8, 2021

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