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  • Line out box

    Puttering around...



    I have several old amplifiers about. None have a line out, preamp out, or anything like that. Some time back, I wanted a line out, so I built one.



    Speaker cord out to the line box. In the line box, there is an input jack and an output jack, which are really just parallel jacks. From the hot side of the input jack, there is a 10K dropping resistor going to the line out jack, then a 1K load resistor to the common.



    A couple of nights ago, I decided to add a bass boost. In series with the load resistor, I installed a 2.2 ?F capacitor. That adds a boost from about 80 Hz on down. Then, I put a 2.2K resistor in parallel with the cap, to limit the boost below 40 Hz.



    It ought to be shielded, I suppose, but I did it all in a plastic deli tub.
    "The Web puts all of the world's knowledge at our fingertips; unfortunately it's mixed with all of the world's bull****************."
    -- Bob Parks

    "A thing is not necessarily true because a man dies for it."
    -- Oscar Wilde

    "No man dies for what he knows to be true. Men die for what they want to be true, for what some terror in their hearts tells them is not true."
    -- Oscar Wilde

    "It is a trap of history to believe that eyewitnesses remember accurately what they have lived through."
    -- Theodore White

  • #2
    I've installed speaker emulated line out jacks in all my older tube amps.

    Comes in handy for direct recording. Theres an extra cap in there to remove the harshness you get from a normal line out. Much better for recording.

    It can easily be put into a separate box too but theres less hum exposure if the cord between the amp and the DI box are short.







    Comment


    • #3
      Doesn't that cap impose a 6 dB/octave rolloff starting at about 1.5 KHz? Seems awfully low to me. Have I miscalculated?



      I hesitate to modify my old tube amps, even mods I know I should do, such as a three-prong power cord. They're not worth much, so I shouldn't hesitate, just go ahead. I tell myself this, but I keep not doing it.
      "The Web puts all of the world's knowledge at our fingertips; unfortunately it's mixed with all of the world's bull****************."
      -- Bob Parks

      "A thing is not necessarily true because a man dies for it."
      -- Oscar Wilde

      "No man dies for what he knows to be true. Men die for what they want to be true, for what some terror in their hearts tells them is not true."
      -- Oscar Wilde

      "It is a trap of history to believe that eyewitnesses remember accurately what they have lived through."
      -- Theodore White

      Comment


      • #4
        I'm also thinking I should add in a switch, bypassing the bass boost.
        "The Web puts all of the world's knowledge at our fingertips; unfortunately it's mixed with all of the world's bull****************."
        -- Bob Parks

        "A thing is not necessarily true because a man dies for it."
        -- Oscar Wilde

        "No man dies for what he knows to be true. Men die for what they want to be true, for what some terror in their hearts tells them is not true."
        -- Oscar Wilde

        "It is a trap of history to believe that eyewitnesses remember accurately what they have lived through."
        -- Theodore White

        Comment


        • #5
          Well theres a resistor between the amps output and the line out jack it straddles so whatever

          load the cap puts on the amp at 8 ohms is infatesimal.



          The cap value is perfect for what it does. The resistor values are good for a 50W head running at

          normal volume. A higher or lower wattage amp may need different values.



          I thought about putting a 500K pot in series with the 470 ohm resistor to vary the level dowmn a bit.

          I suppose I could just put it across the output jack too. You could wire the cap like a guitars tone control

          and vary the speaker emulation, but I never saw the need to.

          Comment


          • #6
            Tried it out at rehearsal this evening. Worked great.
            "The Web puts all of the world's knowledge at our fingertips; unfortunately it's mixed with all of the world's bull****************."
            -- Bob Parks

            "A thing is not necessarily true because a man dies for it."
            -- Oscar Wilde

            "No man dies for what he knows to be true. Men die for what they want to be true, for what some terror in their hearts tells them is not true."
            -- Oscar Wilde

            "It is a trap of history to believe that eyewitnesses remember accurately what they have lived through."
            -- Theodore White

            Comment













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