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Thread: Shielded Cable ???

  1. #1
    Join Date
    Jan 2007
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    Yorkshire, UK
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    4,564

    Default Shielded Cable ???

    Hi

    I am just about to start doing the permanent wiring inside my projector.

    From the back of the DB25 connector should I be using shielded cable to the scanamps or will ordinary cable suffice. Also, what about the modulation wiring for the RGB lasers, is it better to use shielded or should I just use standard cable.

    I have some 7 strand and some 16 strand single core cable. Assuming this is o.k. rather than shielded, as it's only 5 volts which is it better to use, the 7 or 16 strand?

    Does anyone know if a MediaLas USB DAC makes use of the differential signals?

    Any other hints or tips?, or can anyone answer any of the questions I haven't thought of yet?

    Cheers

    Jem

  2. #2
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
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    Default

    I noticed that with my 15K scanner set that if I don't use shielded cable between my DAC and the scanner amp I will pick up enough noise that to be visible in my laser display. The noise went away with shield cable. For that reason, I am using shielded cable with everything, whether I need it or not.

    I only connected the shield to ground at one end up the cable. I heard that is the correct way to do it. But if that is wrong I would like to know.

    Also, I think the shielded cable looks neater.

  3. #3
    Join Date
    Mar 2006
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    2,478

    Default

    Quote Originally Posted by carmangary View Post
    I only connected the shield to ground at one end up the cable. I heard that is the correct way to do it. But if that is wrong I would like to know.
    If you're using differential signal lines, it's right. They should be a twisted pair inside a screen that is grounded at the end that is most firmly coupled to ground. If the signal is a single line and ground, it's not so easy to decide, because it depends how well the grounds are interconnected before interconnecting signal lines are wired in. If the grounds are star-networked and secured with good conductors, it's still best to ground the screen at only one end, as you'll see in internal signal wiring in many commercial hifi systems. If the boards are on insulating pillars you can use the signal cable screens as grounds between boards, but you still have to think about ground loops.

    None of this would be confusing, let alone a serious problem, if it wasn't for daft commercial convenience. Most cables are made grounded at both ends, partly because no maker can assume another maker has any sensible grounding in their systems (a lot of audio gear doesn't even have a safety earth wire!), and partly because they won't go to the effort of wiring a cable differently at each end and adding an indicator to show which end is which. This means everyone is following bad practise unless they carefully avoid doing so.

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