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Projector and cable noise.............

Discussion in 'Projectors, Screens & Video Processors' started by Parmenion, Oct 28, 2002.

  1. Parmenion

    Parmenion
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    It has only taken me 3 months but I have finally got there.......

    The hum that regularly comes out of my speakers has been annoying me for ages. First the Denon amp was looked at, then the Rotel power amps.....next came power leads, then the mains back to the fuse board....

    finally I went through the tedious task of plugging and unplugging everything in all the combinations that I could (until I fell over with exhaustion)

    You can imagine my surprise when I went to clean my projector and in the process unplugged the S video lead.......shock horror!

    No hum...

    plug it back in...............HUM !

    Who could have guessed (Yes I know now, smartypants!) that a lead carrying a PICTURE could be responsible for all this aggravation.......

    All I need to know now is..........can I get a reasonably priced S video cable thats about 25 to 30 feet long, that won't pick up this 'noise'

    Regards

    Parmenion
     
  2. maj74

    maj74
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    Do you mean an S-video cable that won't 'create' all this noise, rather than pick it up?
     
  3. Parmenion

    Parmenion
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    I think I mean both !

    What are my options?

    Regards

    Parmenion
     
  4. Geoffc10

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    All you have done is break the earth loop. Trying another lead may help, but in my case the subwoofer was faulty. No more severe hum through front speakers, although you can still hear the sub hum when in the room and its quiet
     
  5. Parmenion

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    Geoffc10, I'm not entirely sure what you mean......since my original post I have tried a couple of different leads and as soon as anything is plugged into the projector the whole system starts to hum.

    What exactly happened in your setup?

    Regards

    Parmenion
     
  6. Technophobe

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    Parmenion,

    I assume the problem is only when the Projector is running.
    If so I think what's happening here is that some of the leakage to earth that takes place within the projector is passing to mains earth via the svideo's earth lead and then via your dvd player / receiver. I had this problem when I had a Tosh MT1.
    You can prove this is the source of the problem by temporarily unplugging the mains lead from the PJ.
    If the PJ and your amp's earth are at different potentials due to earth leakage currents in your house a current will flow down the Svideo signal earth and noise will be induced.
    Can you give me a little more to go on with regard to how your equipment is connected and powered?

    Technophobe
     
  7. Parmenion

    Parmenion
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    Oh yes ! This sounds like it......

    strangely my projector is a Toshiba MT1 ! ! !

    The projector is at one end of the room, it is connected to a wall socket by its own *kettle type* power lead.

    Running from the projector to a Denon av amp is a long Profigold (sorry................. I'm poor) S video lead.

    connected to the av amp is a Tosh DVD player and a NTL Pace digital STB.

    All is well with no hum..........then the big mistake............I connect Rotel power amps to the pre outs of the Denon. Result.........hum hum hum.......switch the power amps off and the hum disappears.

    The answer I know is to leave the bl***y things switched off !

    The trouble is now I've heard the system with the power amps the differnce is night and day (to me at least....)

    Any suggestions?

    Regards

    Parmenion
     
  8. Technophobe

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    Parmenion

    You didn’t say if the noise is only present with the PJ running, but I will assume this to be the case.
    It sounds like the problem is being caused by the different earth potential of the PJ and the rest of your kit, with a result that current will be flowing down the screens of any leads connecting them.
    Just to prove I’m on the right track here can you try partially unplugging all the phono leads that connect to the pre outs on your Denon, such that only the inner signal pin is making connection but with the outer screen of the phono plug not pushed in enough to make contact. This will isolate the signal grounds between the Denon and the Rotel power amps. You should find that the links still function because the AV amp and the power amps will be sitting at similar earth potentials anyway, but keep the volumes turned down initially just in case. You could try this fault finding approach to all the phono connections as a way of breaking the earth’s.
    I’m assuming the noise is coming from the power amps speakers and not from the Denon AV amps speakers.
    BTW If you have the same problem I had it sounds more like a harsh buzzing than a hum, presumably being picked-up from the lamp or it’s supply.

    Let me know the results and we can continue trying to solve this one.

    Technophobe
     
  9. Parmenion

    Parmenion
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    I'm doing it now,

    as we used to say in a previous incarnation

    *stand by, stand by*
     
  10. Parmenion

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    I can see now I didn't make it clear, yes you are right, the hum (more like a buzzing now you mention it) is only present when the projector is on, ie the lamp is running.

    Doing as you suggest with the phono leads removes the buzzing ! ! !

    Just a quick note, the rotels drive the speakers, there are not seperate speakers driven soley by the Denon (I don't think that makes a difference, just mentioning it.

    Regards

    Parmenion

    p.s. I'm on the hunt whats next?
     
  11. Parmenion

    Parmenion
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    Just a little further info...........

    I cannot seem to do *exactly* as you describe. When I pull back the phono leads from the pre outs, I can't seem to judge it just right, to leave the inner pin in contact with the amp, but not have the outer metal of the lead also touching.....

    maybe it's me
    maybe it's me leads
    maybe it's me amp

    or me Julie !

    anyhoo.............. all I have seem to have done is remove the rotel power amps phono leads from the Denons pre outs.

    Of course it works, but kind of defeats the object.....

    :(

    Regards

    Parmenion
     
  12. Technophobe

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    Your phono plugs must have shorter pins mine by the sound of it.
    I'm a bit busy here at the moment but will post again later tonight with some more suggestions. But I'm pretty sure this is the problem.

    Technophobe
     
  13. Parmenion

    Parmenion
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    A bit of a reversal of fortune...........although removing the phono leads worked, today I tried the earth lead advice.

    No joy....the buzzing was still present....


    Hope very much this all means something..

    looking forward to hearing from you

    Regards

    Parmenion
     
  14. Technophobe

    Technophobe
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    Parmenion

    Have PM'ed you.
    Give me a call if you can.


    Technophobe
     
  15. Parmenion

    Parmenion
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    Well, just in case someone comes across this thread in a future search............

    Technophobe has solved the problem.:) :p :D

    My room contains 4 double wall sockets. Two at one end of the room, two at the other. All of my AV eqipment is conected to one or more of these sockets.

    All four sockets are on their own spur back to the mains.

    The projector plugs in at one end of the room. The amps at the other end.

    Run a (temporary) extension lead from the projector and plug it into the very same wall socket as the amps and hey presto !
    silence:eek:

    I don't know why, Technophobe does. Something to do with varying amounts of current, earth etc.

    All I do know is that I tried plugging the projector into practically every other wall socket in the house without success:devil:

    Silence is golden. Thanks T.

    Regards

    Parmenion
     

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