Mystery of day to day changes in sound quality.

[JohnJo]

The only effects likely to ensue from poor mains waveform fidelity etc are on mains synchronous motors such as those often used in turntables, and in very bad cases in producing mechanical buzzes etc directly from transformers. The latter can be annoying if loud enough and in a quiet enough environment of course! Unlikely to effect sound though.
In a motor powered directly from noisy mains the actual rotation of the motor shaft will be modulated by the mains noise and distortion which will result in extra mechanical noise etc from the motor... not good.
Virtually everything else in a hi fi system converts AC to DC before using the power and this process is pretty much immune from mains issues. Most items will also use voltage regulation which removes all changes in the actual voltage level ie if the mains was varying between 230 and 248 volts it would make no difference whatsoever to the output of lets say a 15V regulator in a pre or CD player. It will stay at precisely 15V as it is designed to.

I could easily design and build a mains regenerator for my own use from surplus parts for very little money but the fact that I choose not to shows the importance I attach to this issue

RFI from the mains, from speaker cable and other sources can be an issue and the sensitivity of equipment to this will vary VASTLY between different pieces of kit. One amp may be 1000 times more likely to be effected than another. This has nothing to do with the mains itself or special wires etc though! You could have a fantastic mains regenerator and then pick it up just the same in 20' of cable between it and the hi fi.... speaker leads are more important in this respect as the RFI is going straight into the power amps output.

The fairly sudden ubiquitousness of wi-fi is a major problem here, as are mobile phones, and the RFI can get in through even small gaps in casework etc. Most good quality RF gear for VHF and above is built in boxes with a fixing screw maybe every 1/2" which seems totally OTT until you realise it has nothing to do with the mechanical strength of the box! Fine wire mesh will also be used over ventilation holes etc for the same reason

Thanks for your engineering input Jez. This is hopefully getting us closer to the truth on this subject. Since sine wave characteristics are, within reason, possibly not so critical given that we are converting them to DC and then regulating it looks like RFI may well be the main culprit of mains borne sound degradation that many people have seen improve with some form or other of filtration on their mains supplies to equipment.

I use a single phase, 240V industrial filter which is basically an inductor in series in both the live and neutral conductors and a couple of caps across them. I've tried different values and found that as you improve the filtering (larger inductor) you lose dynamics especially on supplies to amplifiers. My current Siemens model is a great all round compromise. This type of design looks like it is merely catching RFI.

All this ties up with what Lukasz Fikus from the Lampizator web site has to say on the issue here http://www.lampizator.eu/AC%20FILTER/SILK/FILTER.HTML

[anthonyTD]

RFI is indeed a part of the problem, and the reason I use one of my own bespoke Mains filter in part of my system, which by the way' is now being hand built and supplied by Mark Grant, this filter is the latest version of the original I designed and have been using in my own system for well over 10 years now.
However, I am not totaly convinced that it is wholey responsible for the sonic degradation many of us experience from time to time.
Anthony,TD...

[The Black Adder]

+1 The Mark Grant mains filter is very good indeed.

[danilo]

Power filtering seems as popular pastime in the above
I presume? then that the mains grid in the UK is not as solid as it could be?
Merely curious, as here, in the Pacific Northwest of north america, the power grid is; solid, clean and reliable.
Has been for decades, results of (too?) many massive Hydro Electric dams.
Consequently anxilliarly filtering is low on the average Audio Weenie's Radar.
Although in a few, should be condemned bldgs, internal power can be sketchy.

[struth]

voltages can vary a lot. its an old system on average and a bit stretched at moment. Also a lot of equipment can be euro and want 230, which ours is supposed to be, but its actually 240 still. I can have as much as 260 at times, and lower than 220 occasionally. the regen I use gives me 230 50 hz steady which then get Belkin filtered and distributed.

[Barry]

Power filtering seems as popular pastime in the above
I presume? then that the mains grid in the UK is not as solid as it could be?
Merely curious, as here, in the Pacific Northwest of north america, the power grid is; solid, clean and reliable.
Has been for decades, results of (too?) many massive Hydro Electric dams.
Consequently anxilliarly filtering is low on the average Audio Weenie's Radar.
Although in a few, should be condemned bldgs, internal power can be sketchy.

So is ours. Powercuts here are very rare and 'brown outs' non existant. In fact the quality of the mains delivered up to the local distribution transformer is very clean and so to is the supply of the mains that enters the house. Voltage may vary region to region, but it is constant to within a volt or two. The mains frequency here is closely monitored by the power distribution authorities, as an indication of the load on the grid, and will be kept to within +/- 0.2Hz at all times with the legal requirement that over a 24 hour period, the number of mains cycles is 24 x 3600 x 50 = 4,320,000 exactly.

The problems that have been discussed are caused either by the consumer themselves (in using switched-mode power supplies, or rectifying power reduction devices that will put DC on the mains), or by other consumers who share the same phase as you. It is this that pollutes the mains quality; and since the source impedance of the mains supply is low, interference generated either by yourself or your neighbour remains undamped and unfiltered. There is much that can be done with the former, but little with the latter.

[Marco]

So is ours. Powercuts here are very rare and 'brown outs' non existant.

Brown outs, eh? There've been a few of those here, the morning after a hot curry!

Marco.

P.S [Pedant alert] 'Existent' has an 'e' at the end, not an 'a'...

Please consult Tabatha for some after-hours 'homework'.