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normal phonos vs proper component leads ???

Discussion in 'Cables & Switches' started by laurence harvey, Sep 17, 2005.

  1. laurence harvey

    laurence harvey
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    Hi, have a vierra plasma and tosh dvd, have connected via decent[prowire] phono leads to component in of plasma, the picture looks very good to me but was wondering if I should change them for dedicated component vid leads ? such as qed etc.
    would appreciate any advice.
     
  2. longleyc

    longleyc
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    Yes you should.
    I doubt if the phonos are sufficently screened plus they should be 75/Ohm cabling rating. Profigold Oxypure are okay.
    So this expensive AV hobby requires you go spend some more money :)
     
  3. MikeK

    MikeK
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    It depends how long the cables are and what signal you are transmitting over them.

    Technically speaking, in absolute terms, then yes the cable should be 75 Ohm, well screened, good quality coax, designed for the transmission frequencies in the video band, with correctly fitted plugs.
    Usually, although not always, audio cables are 50 Ohm coax - although personally I very much doubt whether the cable's characteristic impedance makes any difference whatsoever over a short (a few metres) link with an audio signal up to 20kHz, but that's another debate :).


    However what you have to remember is that while you could use the best 75 Ohm coax cable on the planet, the design of the RCA phono plug precludes it from having a 75 Ohm ch. impedance (it's usually around 30-50 Ohms) There are some phono plugs which claim to be true 75 Ohm, however I've yet to see any explanation of how they've managed to do this, given the mechanical constraints. You could argue that these plugs are closer to 75 Ohm than normal types - again maybe true but that doesn't actually make them 75 Ohm. I would concede that there may be, in absolute terms, an argument for "damage limitation" here, but in practice that argument is, IMO, torpedoed to some degree by the fact that the RCA phono sockets on the kit you are plugging into are not these special "75 Ohm" types).
    The real mystery here I suppose, is why we are still using RCAs at all for video when 75 Ohm BNCs have been available for years (to be fair some manufacturers have indeed switched to these) :confused

    I guess what I'm saying is that while in theory component cables "should" be 75 Ohm etc etc - in practice you may find it makes no discernible difference whatsoever, depending, of course, on your equipment and on what cable(s) you are using currently and what signal you are transmitting (eg while there may be little or no discernible difference with a 576i (PAL) signal, the same may or may not be true of PAL progressive, which doubles the signal frequency, or things like 720p/1080i, which are a lot higher again).
    It's really a case of suck it and see!

    The thing to do, if you can, is to see if you can try a set - if you clearly see an improvement, then buy, and if not, don't buy (but do be careful of emperor's new clothes syndrome though :) )
    There's lots of fancily packaged stuff out there which is ridiculously overpriced, and while it will do the job, is really designed to appeal to people's "if it's expensive it must be good" conditioning. Equally though, there is some reasonably priced decent stuff too!
     
  4. pjclark1

    pjclark1
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    from
    http://forum.ecoustics.com/bbs/messages/34579/123129.html

    "The RCA plug and jack, having been designed for analog audio, were not designed to match a 75 ohm characteristic impedance, and their dimensions are such that they can't be matched to 75 ohms. What one can do, however, is make the length of the mismatch as short as possible, which minimizes the impact of the mismatch."

    "But there are technical deficiencies a component video cable can have, which can have dramatic impact upon signal quality, especially where runs are sufficiently long to make the impedance of the cable a significant consideration. With full-blown HD component running at about 35 MHz, the wavelength of the signal, corrected for the speed of propagation in a high-quality coaxial cable, is about 24 feet, making even a six-foot component video cable a significant fraction of the wavelength and potentially a factor in signal quality."

    The theory
    Impedence is not a factor where the cable length is less than 1/10 of the wavelength.
    with a 1080p signal there are no problems with cables under 1m
    with a 480p signal there are no problems with cables under 2.5m
    BUT if your gear is using phono connectors, then the cable becomes irrelavent anyway, as the connectors will have a 50 ohm impedence.
     
  5. Joe Fernand

    Joe Fernand
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    laurence harvey

    As MikeK suggests the best way forward is to try out a cable or two in your system and 'see' if its worth the extra cost.

    Have a look around the AVForums banner adds and threads - you'll find the 'usual suspects' are not necessarily the manufacturer/supplier you may end up shopping with.

    Here's my recommendation - http://www.bettercables.com/componentvideo.html

    Best regards

    Joe
     
  6. per-Sony-fied

    per-Sony-fied
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    FWIW I found QED Silver reference 1M component cable with rhodium RCA plugs better in almost all respects over a JVC £10 component lead.

    Both gave fine performance but the QED was clearly superior on many a DVD and differences came very close on others. To sum up, as an overview with the QED, DVD just took on a more watchable picture, just making the presentation more pleasing and wanting to the eye.
     
  7. laurence harvey

    laurence harvey
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    thank you all for taking the time to reply, very good info, most of it went over my head though :).. but I got the idea. I changed the scart on my ntl box to ixos from an hitachi and cant believe how better it is, so will try some proper components, have been advised to go for qed qunux ??? ..thank you all for your time and knowledge.
     
  8. Nic Rhodes

    Nic Rhodes
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    I find it is easy to demonstrate differences between non 75 ohm cables even at much shorter distances than have been quoted here but even easier is the ability to get good quality cables at not silly money that will do all you need.
     
  9. Peridot

    Peridot
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    MikeK ... That's one of the most well-written and well-balanced posts I've seen in a while and one of the reasons this forum is the best source of AV advice anywhere :thumbsup:
     
  10. Nick_UK

    Nick_UK
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    In theory...... a bumble bee can't fly. In practice, we know it can :)
     

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