Electrical interference


Some of you may have seen a topic I posted a couple of months back where I was getting violent pops during vinyl replay. Eventually I found the culprit to be a water pump on a small drinking fountain for the dog. Since then though I’ve been wondering about how household appliances may affect the system.
I’ve never really bothered about that kind of thing. I’ll fiddle about with set up, speaker position, cable dressing and the like but influences outside of the system I’ve never grasped. So if anyone can answer in an “electricity for dummies” kind of way I’d be really appreciative.
The circuit box at my house is the old fashioned type where you have to pull out a two pin plug and rewire it as opposed to just resetting it. It has a fuse for “upstairs mains sockets” and another for “downstairs”. The same with the lighting. Then fuses for the shower, the cooker and the garage.

So now for the questions:

  1. Are these all separate circuits?

  2. I’ve read that certain light bulbs, i.e. LED & halogen aren’t good for the system. If the lighting is on a different circuit to the sockets how can they affect the hifi?

  3. If items on other circuits can affect the sound why is a “separate spur” so favoured?

I’m aware the answer to Q1 might also go some way to answering Q’s 2 & 3.

Thanks in anticipation.


Each fuse represents a different circuit.
Some light bulbs (in my experience particularly compact fluorescents) can cause interference.
I can only say that in my old house, I had a dedicated spur for my hifi. However, the old central heating boiler, on its own seperate circuit breaker, could cause interference when the ageing boiler’s thermostat cut in or out.
A new thermostat on the boiler sorted the issue.
I’d guess that having a seperate spur “reduces” the possibility of interference.

Thanks for that Blythe.
Was the thermostat difficult to replace?

Steve O

Hi Steve - By your description it does sound like the electrical wiring in the house is fairly old. When did you last have it checked by an Electrician to make sure all is well ?

The old mechanical thermostats tend to arc slightly as they open and close and this gets worse as they age - the contacts get dirty and get pitted. The arcing generates wideband RF which couples through (and radiates from) the mains wiring in the house and couples into sensitive items in the system (phono stages).

Wall thermostats are easy to change - only a couple of wires and your done. If you’re unsure then a Heating Engineer or Electrician will be able to advise and fit a new one.


The house was completely rewired in 1986 when we moved in. The thermostat will be that old too as the boiler and central heating system were renewed too.
Guess it wouldn’t harm to replace the thermostat.
Steve O.

33 years is quite a time and your consumer unit is quite far behind the regulations now. I’d be tempted to get it checked out with a view to updating the consumer unit and just checking all is well (decent Earth connection etc), not only for possible SQ benefits but mainly for the safety aspect.

If you’re doing that then it would be a good opportunity to get a dedicated radial installed for the Hi-Fi too, preferably with a separate consumer unit.

I would leave alone if I were you. You have the old rewireable fuses like me and I think they sound better. Mine was done in 2006 and I requested those fuses specifically. By all means, check the connections are tight and even a little tweak on all connection screws will refreshen the contacts.


You may find the thermostat has not two wires, but three plus earth possibly. The reason is that back in the day, the thermostat had a high value resistor wired between the switched line and neutral and this being close to the bimetallic strip meant that the thermostat turned off more promptly than if it had to warm up only by conduction from the air in the house.

Modern thermostats don’t do this because the thermal mass of the temperature measuring device is very low. So to fit a modern two wire thermostat if there are three wires there, just leave the neutral wire unconnected. Normally you would cut it off and insulate the end with some tape as well.

If in doubt, get an electrician to do it!



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The next door neighbour is a sparky but when I asked him about a dedicated circuit for the hifi he looked at me like I’d gone mad.
Steve O.

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Yes Steve, that’s an entirely normal reaction.
It’s only when you hear the benefit that people go,“Aaah!”

Best regards, BF

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As James_n said, it’s really age related interference - modern boilers use a different type of thermostat.
I should point out that mine was the thermostat on the boiler itself, not the one on the wall. I guess both might cause interference but, in the case of mine, it was a buzzing rather than a pop. I guess this was due to the arcing during the opening and closing of the contact.
My heating engineer replaced the thermostat at the time of a service as he reported it was very slow to react. It was then I realised the buzzing I’d heard through the system had stopped :slight_smile:

I imagine an immersion heater might show the same symptoms of a buzz or pop.

Thanks for the input guys.

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