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It seems to me that the harmonic currents produced by power supplies regulated to meet EN61000-3-2 are as much a cause of transformer hum as DC offset. The harmonic currents cause more heating because eddy current power dissipation is proportional to the square of the frequency. You can google the EN to see the regulated limits up to 39th harmonic. If you have more than one transformer the chances are they will interact. The bigger they are the more so.
If you Google Power Factor you will learn quite a lot.
I’m not knocking these products but be sure you know what the real problem is. Personally I think Naim need to help us more. I have certainly reduced 500PS hum to normal level with PowerLines and posh MusicWork mains block. I’m still trying to understand the reasons for this.
I‘ve heard good reviews about PS Audio power regenerators. I didn’t try them yet. But I talked to PS audio support, and they said, that power regenerator completely eliminate all problems (including DC) in the mains.
And as I understand these units are NOT filters and are NOT conditioners. They actively regenerate power output, unlike other devices.
This got me thinking… does anyone know if Naim adopt capacitive PF correction across their larger transformers… I think if I am right under EU legislation for the larger power loads they must do… but I can’t remember hearing about this before… I don’t really want to take my 250 apart to check, but for a large transformer these would need to be fairly large caps.
I saw a compliance statement in the Power Supplies Manual. It did not say which Part of the EN was applicable.
The interesting measurement to take is the mains current drawn during the mains cycle at various loading levels. Some modern oscilloscopes can do the Fourier Analysis. If the current waveform doesn’t look much like a sinusoidal wave the PS would not be presenting as a linear load. A sinusoidal wave with a phase shift would indicate some reactive elements in the load.
I doubt the transformer would be a totally linear load, Not least as the PSU uses semiconductor rectification…
Of course this gets into one of the areas where we see so called linear power supplies are not really linear… or not as non linear as some SMPS but certainly not totally linear.
The EN I quoted details the permissible harmonic current ‘amplitudes’. A picture tells a 1000 words so no idea how close to load linear it gets.
From what I read a bad power supply could have a power factor of 0.3 (load linear = resistive load = 1). Some articles suggest that power factor correction can bring the PF up to 0.7.
Interestingly the reason for these standards are
Like 3 phase supply the user can obtain more power from the grid than the meter can measure. A fudge factor (the PFC) is used to get a fairer measure of the energy consumed.
Non linear loads result in neutral current flows (AC is theoretically zero over the cycle) back to the generation equipment introducing safety issues, requiring larger conductors, and shortening the life of motors and transformers.
@Richieroo may be interested. Whilest 50hz may not present issues for conductor design (solid is as good as filament) the situation (skin effect) changes as the frequency increases. By 2khz it could have a significant effect. What quite a few of us know is that the use of a mains block and better power cords does help. We can put 3 x 2m cables between the poweramp on the wall and the more sensitive equipment plugged into the block. Hum is reduced and SQ improved.
Hi, there I see no reason why correction can’t take the PF to 1, or pretty close, for certain applications.
The reason for the standards as I see it are two fold for domestic consumers/market:
to aid efficient utilisation of the electrical distribution infrastructure and domestic wiring, and to assist consumption pricing more accurately aligning to consumption cost.
minimise mains distortion caused by poorly power factored loads causing non linear loading (important to my mind for larger ‘linear’ power supplies and SMPS )
Yes, I don’t think there is anything contentious here… just a few unknowns with our friends at Naim on how they PF correct their larger PSUs. I guess it would only raise an eyebrow if they don’t…
I am afraid my personal oscilloscope is a modest digital twin trace one…but it usually is adequate for my needs
And yes if I had the time I could perhaps create a jig and measure The PF by comparing current phase with respect to voltage phase
My cables (Powerkord Evo 500’s) are 1m and all go back to the wall socket. It has definately calmed the NAP500 transformer down … is this the enhanced skin effect of the woven cable?
I assume the woven fabric within the power cord stiffens it up and alters dielectric and vibrational properties of the cable. I have not read much about cable properties.
The photo from Wikipedia shows how the skin depth varies with frequency. I recommend reading the Wiki article on skin effect. It’s for a HiFi cable designer to understand the physics and design for purpose.
The EN I quoted regulates up to 39th harmonic (just below 2khz at 50hz mains). The amplitudes have to be maxed in the range of 1-3% according to harmonic at the input to the Power Supply. As the energy output of the supply varies the charging time varies inversely which will effect the harmonic structure of the current.
Most people will only think of the mains as the only source of alternating current. They do not realise that electromagnetic effects are produced when AC current is drawn. These are like ripples on a pond from lots of varying sized stones being constantly thrown in a different places compared to the massive stones represented mains. But they do interfere. The same is true of signals on an Ethernet cable as you have been finding, but in a different frequency domain. Like the big pond there will be quenching from powercord effects but I am not qualified to advise as it requires proper research.
The bigger the power supply the bigger the stones being thrown in and then the eddy current heating effects which are more important at higher frequencies come into effect.
The non linear current load is caused by the rectification. The ripples of the harmonics it contains feed to the other connected HiFi devices. They all disturb each other.
I think Phil, many on here almost certainly appreciate that electromagnetic and usually RF energy originates from cables like Ethernet and USB leads, although they are shielded and/or twisted pair so the emissions are very low (although USB less than 3 deliberately breaks this balance for signalling!)
I guess strictly these are not AC as they don’t average out to zero over a duty cycle… they are more PCM, and I each transition creates a burst of energy … and of course DC creates a magnetic field… Fleming’s right hand rule … for those who remember their O level / GCSE physics.
I was trying to lead Richieroo towards an answer for his question about his Russ Andrews Powercords.
The difficulty with expensive HiFi is understanding the implications of buying a particular accessory (eg better powercord - better at what though). I think I now know what sound to expect from the music I play. I know there were albums that just did not sound right once upon a time. Now there are very few bad ‘uns’.
If you are like me you are intrigued by the Ethernet mania thread. Personally, I am put off products that require tweakery to get the SQ you think you are buying into. In time I hope manufacturers will be forced by law to produce meaningful legally binding specifications.
I do worry that some people on this forum are not getting the best from their boxes.
Phil… interesting, my observation would be that tweaking for some is a big part of this hobby (and many other pursuits and hobbies) … but absolutely not for all… and specifications really don’t mean very much in terms of domestic hifi and expected performance…which I guess Is why other than physical dimensions most specs are pretty useless.
There is something very intangible about HiFi sound. I feel that dealers don’t do enough to earn their very generous margin. Naim are also to blame. My first factory visit left me feeling my 282/300 was better than top of the range. Seems they may have overcome that. Undoubtedly the boxes can sound wonderful but you don’t know and users don’t meet up enough. How else can one know whether one is getting what one pays for.
Take the issue of this thread. Well Naim blame hum on mains quality. The cause can be, and I do indeed get short burst, but there is good reason to believe that Naim power supplies do enough to reduce mains quality to each other. If I had a scope I’m sure I would investigate further. PowerLines to everything (Non Naim also) and a good mains block do help, but why not help customers more with detailed advice. I really can see legislation requiring higher standards coming. The E.U. is set on standardising charging equipment for portable devices to reduce 51,000 tons of associated waste - Apple Lightening connector will be banned.
