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[Poll] A poll on whether Power Cords make a difference

Discussion in 'audio' started by duckworp, Jun 14, 2018.


Do Power Cords Make A Difference?

  1. Yes they do make a difference

    145 vote(s)
  2. No they don't make a difference

    166 vote(s)
  3. I don't know

    53 vote(s)
  1. Ragaman

    Ragaman Mentalist

    This made me laugh, I began reading with my serious face on, thinking I was about delve into some serious thinking on the universe, (something I would welcome BTW as it's a huge passion of mine) then that last line, had to smile :)
  2. mattgbell

    mattgbell Help the elderly and unwell!

    Perfectly understandable, Tony.
  3. h.g.

    h.g. pfm Member

    A clue might lie with the kinds of people that can hear differences between mains cables and the range of other home audio hardware that cannot be distinguished by listening alone. Golden ears? Tarnished brains? Or something else?
  4. John Phillips

    John Phillips pfm Member

    Jim Audiomisc did reply but maybe didn't address that question.

    Generally speaking you can't say for sure that a mains RF filter will be benign at lower frequencies. It will always present some inductance at all frequencies, in series with the inductance of the mains itself. Enough series inductance in the mains will impede the charging of the reservoir capacitor in a linear power supply. So the filter (+mains) has to be good enough. So the question is "is it good enough?"

    The UK mains at a domestic socket typically has, AIUI, about 750 microhenry inductance. The common mode choke in a 15 A mains filter may add about 50 microhenries differential mode inductance to that (but DM inductance is not always specified for mains CM chokes so I am not entirely sure of the figure).

    I have also not done a real worst-case calculation (for a big power amplifier) but if kit is designed to cope with the normal mains then adding a good high-current RF filter looks OK. But a smaller mains filter might add too much impedance. I have no feel how small is too small.
  5. Purité Audio

    Purité Audio Trade: Purite Audio

  6. awkwardbydesign

    awkwardbydesign Officially Awesome

    Thanks, that's what I was thinking of, but didn't have the language to express.
  7. Jim Audiomisc

    Jim Audiomisc pfm Member

    In general terms any filter - or length of cable - will add some series inductance, series resistance, and shunt capacitance. To go further someone would need to determine the values. But note that your mains power connection is essentially a series of lumped items (sockets, ring connections, etc) linked to/by a network of transmission lines and other complicated items - e.g. light fittings that act as unbalanced stubs.

    So if you are worried about the effects of an RFI filter or the cable from the amp to your wall socket because of the impedances and/or RF involved, all these items have to come to the party! :)

    Where did you get the value you quote for a mains socket inductance? And what would be the comparison capacitance and effective transmission line impedance? I suspect these vary but the ranges of values are known given that manufactures design and flog the obnoxious 'powerline' data home feeds. But I've not found a reliable set of measurements for these values which I would expect to vary over quite a wide range from case to case.

    The CM/DM ratio of a CM choke should be reasonably high because of the topology. But again, this will depend on the design details. How they compare with the inductance of a mains cable is something else I'd be interested to know. The general effect can be seen from Fig 2 on

    To calculate it, you'd need to know the sizes and positions of the wires and ferrite to be able to do the required integrals - or just measure one. :)

    You can, of course, fit RF filters that just use shunt caps/snubbers, not inductors, and they won't add much series inductance. But you are then relying on the inductance and resistance of the mains cable for them to work.

    In practical terms the only point I can add is that my experience is that when I've encountered mains RF a filter works but a change of mains cable didn't.
  8. rn82497

    rn82497 pfm Member

    Ragaman - followup the Shape Dynamics reference if you find GR/Cosmology interesting. Also try "The Causal Universe" - interesting arguments about direction of Causality ;-)
  9. John Phillips

    John Phillips pfm Member

    Reference mains impedances are given in IEC725:1981, "Considerations on reference impedances for use in determining the disturbance characteristics of household appliances and similar electrical equipment".

    And there are comments about UK specifically, from a source that looks reputable, at
    "Impedance of the LV Network
    This is defined in IEC725:1981[5] as
    Z=(O.4+jO.25)ohms = O.4ohms + O.8mH

    This represents the entire impedance of the generating system including the LV, MV & HV networks as seen by the consumer. For major countries, using the 230V supply system, at the extremes the UK is the best at less than (0.25+j0.23)ohms and Ireland is the worst at (1.03+j0.55)ohms both at 90% of locations. In the UK only 2% of consumers have supply impedances above the standard value whereas in Ireland 40% have. These are 1981 figures but there is no reason to think that they have changed substantially over the last 19 years."
  10. Jim Audiomisc

    Jim Audiomisc pfm Member

    That may make sense as a reference for 50Hz and its low harmonics for the entire path from the generator. But I doubt it will reliably give us the wall-socket impedances up in the RF. I'd expect those to vary wildly with frequency, choice of socket, and even when someone moves a mains cable connected to another socket in the house. Normal domestic house wiring isn't built to act as a well-defined wideband RF transmission line!

    And connecting something to another socket in the house would make a path between them that *doesn't* have to go back to the generator. Hence a totally different value for RF between the items. Shame really as 1 mH in the way might stop people selling 'powerline' systems. 8-]
  11. John Phillips

    John Phillips pfm Member

    I agree. And I have seen some material from "powerline" sources showing such variability. However I suspect the IEC figures are good enough for thinking about whether the current peaks necessary for charging a reservoir capacitor are obstructed by too much inductance. Such as from a long mains lead or a common mode choke in a mains filter.

    And a quick GNUCAP simulation with 50 microhenries extra (from a 15A CM choke where the CM/DM inductance ratio is 30) suggests a 15 A rated mains filter will have negligible impact on even a high power amplifier.
  12. Jim Audiomisc

    Jim Audiomisc pfm Member

    In turn, yes, I'd agree that the values quoted are probably a useful reference when thinking of charging traditional capacitors in traditional PSUs. But I'm less sure about switched mode ones.

    I also doubt that the common types of RF mains filters would have much effect on degrading in some way the cap charging of the PSUs in power amps. But in practice all I've done is try filters and found that for me they fixed mains garbage ingress when this was needed without having unwanted audible side effects. That said, given a good PSU this shouldn't in my experience be needed normally, anyway. The problem is the plethora of units, PSUs, etc, which presumable almost anything will happen to someone!
  13. whatsnext

    whatsnext Naimless

    Numerically we seem to have reached a stable ratio and volume of voters.
    Duckworp your thoughts?:)
  14. S-Man

    S-Man Kinkless Tetrode Admirer

    To Duckworp?
    Is it a verb?
  15. Marky-Mark

    Marky-Mark pfm Member

    For sanity's sake, I implore you all to

  16. whatsnext

    whatsnext Naimless

    You might have overlooked duckworp is the OP, nounish
    So wondering if he joys in the poll
  17. Sue Pertwee-Tyr

    Sue Pertwee-Tyr Well, I can dream, can’t I?

    No, I prefer Duckworp as a verb, and will use it in future wherever I think it fits. My provisional definition would be to passively aggressively crap on a thread by pretending that you are taking it seriously, and adding helpful observations, while in all probability smirking to yourself all the time.

    I should clarify that using the name of the OP doesn't imply it applies to him.
  18. whatsnext

    whatsnext Naimless

    Beware the Trump, treat with caution.
    Waistcoats are go
  19. MikeMA

    MikeMA pfm Member

    If you start doing that people will make all sorts of claims confusing correlation with causation.
  20. DonQuixote99

    DonQuixote99 pfm Member

    As if they don't otherwise?

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