Mains extension blocks




Traditional incandescent lamps are the answer!

Ok so they were terribly inefficient and burnt out comparatively quickly, but like the clammer to SMP’s from Linear some changes “for the better” turn out to be worse…for sound quality!


Apart from the Simon “Yep”. Something to ponder & to put the frighteners up those who are “noise” adverse. These low voltage “transformers” are not all what you might think. A real transformer can be used but are very inefficient & loose a lot of energy in heat. The products sold for this purpose, many marketed as electronic transformers, are switch mode power supplies (SMPS).


I have some vintage light fittings in which I still use old fashioned incandescent bulbs, but of course, they are no longer sold. I even stockpiled some for a chandelier in the living room, as it would look hideous with most modern bulbs in it. Things have changed a bit now, though, as some ‘filament’ LEDs look quite similar to old fashioned light bulbs, and they don’t all emit electrical noise.


I tended to avoid 12V fittings as they can be bulky, or there’s the extra hassle of hiding a separate transformer. I’ve noticed transformers that hum, and get hot, too. So maybe a well designed SMPS isn’t such a bad alternative. Good luck getting a home demo of a 12V light fitting, though!


Richard, are you saying you plugged the surge protected block into your dedicated supply and it’s presence had the effect you describe? Or was it proximity from an ordinary socket.



Phil, it was plugged into a socket which is on the same CU.


Richard, So you are saying that surge protected blocks on any ring main on the same CU as the HiFi could have an adverse effect?


Phil, when I was in the music room and I had the surge protected block plugged in, it definitely had an adverse effect on the sound of the LPs I was playing - it made it sound like the cartridge was past its best. It was obvious enough that i had to stop work to check the TT setup. Unplugging the block restored the performance I was used to.


Richard, Thanks for clarifying. phil


A surge protected block plugged into any socket of your house, even on a separate cu to your hifi, will affect your hifi. That’s a fact.


Please relate how this is possible?


From my own experience as a consumer and running technical support I can honestly say the biggest source of mains noise is from plug-top power supplies/chargers. The amount of rubbish they send out has to be seen to be believed. Now I know this is going against all-of-the-above but my suggestion is do NOT plug plug-top (SMPS) or chargers direct into your mains. Always use a filtered mains strip. So rubbish into the strip and then strip into the wall. Don’t believe me then just connect a scope across your mains! btw also a fan of balanced transformers but that’s another thread perhaps…


Yes not all mini SMPS are bad, far from it, in fact I have some specialist ones that generate no noticeable noise (using the radio method), but there are as you say some shocking ones that I am not sure are legal in terms of the EMC compliance legislation, but trading standards I suspect don’t have the resources to follow up.

The main culprits for electro magnetic noise are Home Plugs or Power Line Adapters and bad LED lighting … the former exploit a loop hole in the EMC compliance legislation to be lawful in their use. The EU a few years back were really pushing Powerline Adapters technology for consumers and Ofcom and others were guided by this.

I think now Ofcom will only get involved with Home Plug or Powerline Adapters. if a ‘Protected User’ is impacted by their use through emitted radio interference .

Indeed I personally required Ofcom to investigate this a few years back… Ofcom had the offending Powerlines removed in a particular property… this was done with the agreement of the property owner. In this case the Powerlines were radiating from the mains wiring feeding the property as well as creating a relatively strong field approx 50 metres around the house on the property. Using Ofcom’s covert radio detection equipment, it was relatively easy to track down.

There is some good news, a few years back cheaper plasma flat panel TVs had become notorious for EM noise and interference, but technology has moved on and current screen technology is far better behaved…

The issue with Poweline and Home Plugs is that the interference they produce will very much vary from property to property and how the property is connected to the Utility supply.

Bottom line, if in doubt, and you don’t have access to the right measuring equipment, use the radio test. Tune an AM radio off station, and it should be a loud hissy sound. Move to a suspect powersupply, digital electronics, light, or even house wiring (for Power Line Adapters) and you hear a loud rasping or motor boating sound… this will get louder and even possibly overload the radio as you get closer to the source. This is RFI and WILL compromise to varing degrees sensitive electronics such as quality audio equipment.


Something we probably agree on :slight_smile:

Note also there are good homeplug devices and bad ones. I’ve also been talking to Ofcom right back from before even the Homeplug 1.0 standard (in those days they were 14meg devices!) and I’ve heard several stories back from them about products and issues.

This is like plug-top power supplies, there are terrible ones and not so terrible ones though, tbh, I think they are ALL bad. From customer feedback it seems the very worse ones seem to be the ones that come with the the later BT HH routers.


I find this thread terrifying, far more so than the Brexit thread… Each new post is worse than the one before - I’m now a nervous wreck. My house is full of those evil things, LEDs, chargers, etc. Isn’t there a glimmer of hope somewhere in this frightful world?


Hi i would be surprised if the BT HH router power supplies are very bad, as interference here would compromise xDSL performance - and that is not in BT’s or the consumer’s interests but I have no way currently assessing them.

To your other point, a SMPS can be built to be largely benign, and I have such a ‘plug top’ PSU , its just in cutting corners to keep costs down filtering is omitted or is compromised and so issues can arise on cheaper consumer items

With PLA technology, by its very nature of how it functions it will create near field RFI, (as essentially it is an extremely wideband radio frequency transmitter and receiver with many many phase modulated carriers). Unless you were connecting to a fully shielded mains wiring infrastructure - including connected compliance’s - hardly feasible.

Improvements have indeed been made some of the later standards to increase efficiency and reduce idle interference - as well as radio spectrum gapping has been introduced to protected user radio services. The latter has helped reduce interference to some specific users of the RF spectrum, but it doesn’t necessarily address interference to non RF applications like sensitive audio equipment, and of course inter modulation distortion occurs on connected mains electronics - as many/most? are not expecting to see this RF energy. The inter mods fill across the spectrum gapping albeit attenuated - so even gapping is not a complete fix for Protected Users - but its a step forward for certain radio users


Breath slowly for a minute - and you will be fine :grinning:
Other than PLAs not all of these things are bad, its just for the layman there is no way of knowing… and if you were listening to your Naim you might think its sounding off this evening etc and blame it on the weather, kids, the cat or what ever… when actually its a dodgy LED light in the under stairs cupboard.

So if you are concerned - do the radio test - if nothing untoward shows up you can rest easy. If you hear loud alarming rasping nosies where you are not wanting to or expecting then simply change the errant devices out.


I blame the EU, we never had these problems before we joined :grinning:

However, I have found Olsen makes very good mains extensions blocks and I use these. They are not audiophile prices, but they are excellent quality and they’ll more or less make it to your specification.

I have unplugged the TP Link HomePlugs in my house and I cannot hear any difference. I have a separate consumer unit for my HiFi so that may affect the results. Benchmark Media has some interesting papers on RFI.

However, I find Hugo sounds better when it is not plugged in to the mains. So I believe its PSU may be a culprit for RFI. It fails the AM radio test too. DAVE on the other hand seems to be well sorted in this respect (just as well as it’s useless when not plugged in to the mains).

Have no fear though, good times are just around the corner.


Hi - get your Hugo PSU swapped out - they are not all the same in my experience. If it fails the radio test and the Hugo sounds different with it connected or not - something is very wrong. If some of the filtering compoenentry fails over time it will start to radiate.

I checked my Hugo PSU a few months ago and it was almost silent on the radio test - but I will check again out of curiosity as it is a first generation Hugo supply - to ensure nothing has failed.

Point on RFI and electro magnetic interference - much of the interference conducts through the air - (technically dielectric) and so separate wiring within relatively close prxoimity will only tend to help isolate lower frequency noise but won’t necessarily prevent RFI which can couple across conductors and chassis. So prevention here is better than cure…