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Converting mon amplified audio out to lstereo line input (line level?) in

Discussion in 'Electronic Basics' started by JazzMan, Jul 28, 2005.

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  1. JazzMan

    JazzMan Guest

    I want to use my TV's built in speakers as the center channel
    for my old ProLogic surround. My TV has stereo audio inputs,
    my ProLogic receiver/amp has only amplified center outputs
    in mono. I had thought about trying to take my TV apart and
    cutting the speaker wires loose from the main board and then
    running them to a jack (added by me) on the back panel, but
    the TV is just too heavy for me to work with due to a blown
    disk.

    So, I thought about just making a cable that went from the
    amplified center out on the receiver to the audio input
    jacks on the TV, turn the receiver center volume way down,
    the TV volume way down, and then hope for the best, but I
    think there will be a problem with the linearity of the
    volume control this way, plus it just seems like an inelegant
    hack job.

    My question is, is there a simple, easy way to convert the
    amplified audio in mono from the receiver/amp to a line level
    source in stereo? I have a center channel speaker but can't
    use it because it physically won't fit within 5' of the TV
    where I've got it mounted now.

    Thanks!

    JazzMan
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  2. PeteS

    PeteS Guest

    Well, if you are trying to make a mono input (on stereo outputs), then
    simply sum the channels.

    Take your left and right channels, from now on L and R

    Now use a simple summing amplifier to yield L+R. There's your mono
    output. You may want to buffer each of the inputs to the summing amp.

    Cheers

    PeteS
     
  3. JazzMan

    JazzMan Guest

    I need to go the other way. I have a mono amplified output
    from a receiver/amplifier, this output is designed to run
    a center speaker. The TV has stereo line-level inputs to
    run the stereo speakers in the front of the TV.

    The only reason I want to convert mono to stereo is so that
    both TV speakers are being used, otherwise the center channel
    audio will be off center. The TV doesn't have a mono input.

    JazzMan
    --
    **********************************************************
    Please reply to jsavage"at"airmail.net.
    Curse those darned bulk e-mailers!
    **********************************************************
    "Rats and roaches live by competition under the laws of
    supply and demand. It is the privilege of human beings to
    live under the laws of justice and mercy." - Wendell Berry
    **********************************************************
     
  4. Then your original question wasn't clear. At the very least it
    was too cluttered.

    Take the mono signal, and feed it into both audio channels of
    the tv set. You can get y-adaptors that will do this, or just
    get a cable that fits into your receiver and splice it to a cable
    that will fit into your tv set. Wire the two tv set end plugs
    in parallel
    __________left jack of tv set
    |
    signal--------|
    |__________right jack of tv set

    ground--------ground of tv set

    If you're fussy about signal levels, then add an attenuator at the output
    of the receiver, a pair of resistors.

    Michael
     
  5. JazzMan

    JazzMan Guest

    Yes, I was aware my original question was not clear enough, but
    I'm glad I got my though across on the second try. :)

    For attenuation, is a resistor enough? What about issues of
    scaling, i.e. small changes in amplifier output produce wide
    changes of volume on the TV speakers?

    JazzMan

    --
    **********************************************************
    Please reply to jsavage"at"airmail.net.
    Curse those darned bulk e-mailers!
    **********************************************************
    "Rats and roaches live by competition under the laws of
    supply and demand. It is the privilege of human beings to
    live under the laws of justice and mercy." - Wendell Berry
    **********************************************************
     

  6. Use a pot instead of two fixed resistors so you can adjust the level.

    --
    Link to my "Computers for disabled Veterans" project website deleted
    after threats were telephoned to my church.

    Michael A. Terrell
    Central Florida
     
  7. kinyo

    kinyo Guest

    JazzMan,
    You do need to attenuate the amplified outputs using resistors and/or
    capacitors.
    The attenuator circuit would depend on the ratings of the output
    amplifier ... how many watts into what ohms ... and it is also
    important to know whether the (-) terminal of center speaker is ground.


    If the (-) terminal is not ground, the circuit will require some sort
    of dc isolation, hence some capacitors or isolation transformer is
    necessary.

    If the (-) terminal is ground, the attenuation circuit would only
    consist of two resistors as voltage divider. If say the center
    amplifier is typically rated 25 watts into 8 ohms, it wouldn't hurt to
    start with 100 ohms and 10 ohms resistors.
     
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