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Effect of capacitor across mains.

Discussion in 'Electronics & Electrics' started by ChoppedLiver, Apr 22, 2014.

  1. OP
    OP
    ChoppedLiver

    ChoppedLiver Member

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    Yes i know this, is why i asked, and i thank all for their thoughts so far.
    I'm not trying to muck people around, but today has been very busy for me.
    So I apologize for not being able to fully explain myself earlier.

    Now that i have time, i shall explain further, but, this is going into the snake oil / audio cables are all the same territory..

    I have been made aware by others, that by putting a 0.47uF np cap across the mains in a house, it will 'alter' the sound of a hi fi system.
    I have tried it and verified that this really is the case.

    My reason for this post was to try and understand how the f... putting a cap across the mains could have an effect to such a degree that multiple people can verify it easily.

    my thoughts are that capacitors react to ac waveforms at different frequencies (dependent on value).
    But how does that manage to affect any audio equipment which in itself will normally have either a switch mode or linear power supply, that also has its own filtering system comprising of capacitors, diodes, and regulators as a minimum.

    Not forgetting that there are then all the audio circuits after the supply stage as well.

    I'm theorizing that by acting as a line filter to some degree, that it allows the equipments power supply to act more efficiently for its own internal needs, rather than having to combat external mains borne noise.

    So, there you have it. an item that does result in a change to reproduced audio.

    I personally would like to know if my suppositions are correct or not.
     
  2. [SweN]

    [SweN] Member

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    did you know that there is even a small branch of medicine based around the placebo effect? im not even kidding.

    as for this, well i have my doubts, but there are some pretty knowledgeable electronics people on here, but im not sure that title will tickle their attention.
     
  3. Symon

    Symon Castigat ridendo mores

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    dakiller is our resident audiophile, I'm sure he'll be along to confirm or deny such things.

    However I'm curious as to how you determined that there was in fact a change? If you only used your ears then I think it would be down to confirmation bias. If you used something like an oscilloscope, then post up your results.
     
  4. cvidler

    cvidler Member

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    Unless you've confirm effect with double blind ABX testing, you've got proof of squat
     
  5. oculi

    oculi Member

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    Scientific or religious variety?

    how did it change the sound OP? do some blind testing, should be easy to do with two extension cords, one with the cap and one without, both wrapped in the same colour oxygen free electrical tape where the cap may or may not be installed.
     
  6. mAJORD

    mAJORD Member

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    I'm sorry. But you've been placebo'd

    I don't even know where to begin on why it is not the case. Especially since you haven't described what aspect of the sq you perceive has improved
     
  7. RobRoySyd

    RobRoySyd Member

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    There's people around who're convinced that "special" mains leads will makes a difference to the sound as well. There's also "special" HDMI cables that'll give you a better picture.
    None of this can be verified by any instrument other than your eyes and ears.

    http://kevinboone.net/hifimainscables.html
     
  8. OP
    OP
    ChoppedLiver

    ChoppedLiver Member

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    My point exactly.
    "Oh snake oil/placebo/must be double blind test etc."

    but hey, thats fine.

    as i said, im trying to find a logical explanation as to what may be happening, or why it makes a difference.

    if your so sure it has no effect, then buy the cap described, and try it yourself.
    prob only about $10 for the cap.

    and i didnt say it improved the sound, just that it had an effect, or changed the sound.
    better or worse is up to the individual..

    Thats the extent of how much ill try to argue my findings.

    If i told you what the difference is with or without the cap, then won't that potentially skew the results of those that try it ?

    Ssssssssssssssssssssnake oil, or, not. you decide for yourself.

    I actually would like to get back to the theory of what a cap will do to the mains, and what possible effects that might have on other devices.
     
  9. cvidler

    cvidler Member

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    ah the catch crys of the snake oil dealer.
    'try it yourself'
    'it did something, I can't/won't explain what'

    Unless you've 100% reliably identified the 'change' in double blind tests, you're placebo affected, and not thinking objectively.

    you've been duped.
     
  10. maddhatter

    maddhatter Member

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    Considering the first thing your amp is doing internally would be converting AC mains into clean, crisp full wave rectified filtered DC, I'd say the cap would be doing FA.

    Unless you've got some real noisy AC waveform ala modified sinewave or some such at the premises...
     
  11. 2xCPU

    2xCPU Member

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    Please tell us more about this magic cap.

    I've got 0.47uF caps from 0805 up. Does size matter?

    Does it matter if it's a ceramic, polyester, styrene, silver mica, green cap, teflon, paper, MKT or bipolar electrolytic?

    What about multi-layer vs monolythic. Any difference?

    2.
     
  12. cvidler

    cvidler Member

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    silver mica is better, because you know silvers like super conductive and shit yeah, adds warmth and air to the music.
     
  13. 2xCPU

    2xCPU Member

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    I also thought the silver mica may be the go because they look so old fashioned it might help getting the 'LP analogue' sound from MP3 files.

    2.
     
  14. RobRoySyd

    RobRoySyd Member

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    What you're saying is something that as far as I'm aware is impossible to verify by any scientific method. If you play the same piece of music twice it will sound different even if nothing has changed other than you're hearing it for the second time. The same will apply for the third listening and the forth. That's why some people can go to the cinema and watch the same movie 100 times, each time they find something they didn't notice before in the movie. Rinse and repeat enough times and by the end you are forgetting what you noticed at the first viewing.

    To put that another way. If you had 100 test subjects and told them that 50% would be given some drug that would change an unspecified something about them and the other 50% a placebo and actually gave all of them the placebo I think almost all of them would report something had changed. Something did change of course, they all took something.

    I think there could be a way to construct a double blind experiment however I'm not good enough on the whole statistics and probabilities thing to know if the results would be valid.
     
  15. Doograsss

    Doograsss Member

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    Difficult question to answer this.

    At a low level, placing a 470nF cap between Active and Neutral will give a low impedance path for certain frequency currents going in and out of the power supply.

    The impedance for a given frequency depends on the size (and physical construction to an extent) of the capacitor, where each capacitor has a self-resonant frequency where its impedance is lowest. Either side of this self-resonant frequency the impedance increases exponentially.

    The theory behind making a difference to the output of an audio amplifier by a small alteration to the input of its power supply is tenuous.

    A switch mode supply (boost or buck) operates on the premise of high frequency transients far more nasty than those you'd expect from your mains. You'd expect the inductor and output cap(s) to knock anything nasty off.

    An old style rectifier with filter will also stop these transients extremely effectively, as it will have a huge inductor and bulk capacitors after the rectifier.

    So, it really shouldn't have any effect at all on the output of your audio amplifier...

    Of course this is the most ridiculous simplification, but meh!
     
  16. oculi

    oculi Member

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    not at all, it just means that if the change due to the capacitor is smaller than the measurement/whatever error then you won't be able to pick it. If he listens to a track 10 times, 5 times with cord "Heads" and 5 times with cord "tails" (while blindfolded and someone else randomly swapping the cables based on a coin toss) and records each time if the track sounded better or worse, you can check if "better" lines up with either of the cords, and then check if the "better" cord had the capacitor or not.

    the result will either be track X sounded better with the cap, track X sounded worse with the cap or that there is no relationship between how good the track sounded and the cap being present or not.
     
  17. starkers92

    starkers92 Member

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    Sinewave input, and a CRO on the output of the sound system?
     
  18. cvidler

    cvidler Member

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    Oh, but you can't measure audiophile qualities. warmth, timbre, air,

    :rolleyes:
     
  19. RobRoySyd

    RobRoySyd Member

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    That methodology did occur to me except I stumbled on the test being "different" rather than "better" or "worse". My other issue is how statistically significant a sample size of ten would be. I guess if your test was repeated 10 times with 10 different subjects it should reveal an answer.

    To try to answer the other question raised here I think we need to look at the system's transient response rather than it's steady state response.
     
    Last edited: Apr 24, 2014
  20. dakiller

    dakiller (Oscillating & Impeding)

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    Please post more on your testing methodology, as well as all the equipment used.
    If you knew just a small fraction about me, you would know that I am 99% the scientific variety.

    I do believe in a few audiophile claims that are extremely hard to prove scientifically that there is a difference, too many very smart people that I trust their judgement on giving independently the same accounts, but that is on things that are much closer to the signal chain than the mains power coming out of your wall.

    When you have mains power which goes through filter caps, transformers, rectifiers, DC smoothing capacitors and usually voltage regulators as well; if you really can show that a cap on the mains externally has such a noticeable effect, my real conclusion is that the power supply of the device is completely inadequate and the device is hardly 'audiophile' to start with.

    Before we go much further, you need to show that you really are getting the results you think. Your own brain is the easiest to fool.

    Warmth is regarded to be dominate 2nd order harmonic distortion, something that valves/tubes contribute to. There are many qualities that are obvious and easily recognisable that don't have good measurements, sound stage/imaging is one.
     

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