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  • #16
    Yup, fair enough.

    Nothing 'wrong' with a perfect gain stage or a cleaner-than-usually first gain stage, not what I wanted to imply anyway.

    Have you considered a folded cascode design and a constant current source at the top?

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    • #17
      Originally posted by uneumann View Post
      The HiZ output is in the output leg of the mirror. The input leg is exactly opposite - it's a LoZ load - unless loaded intentionally by a resistor. The input leg is better thought of as a current sink.
      Doh! I knew I was missing something! Even with the schematic right in front of me, I saw it backwards!

      So as you're using it, you are using the triode as a voltage to current converter for signals, and the current mirror is letting you convert the current back to a voltage through the resistor on the output. The output traces the tube's Vgk verus Ip line for signals.
      Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

      Oh, wait! That sounds familiar, somehow.

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      • #18
        Originally posted by darkfenriz View Post
        Yup, fair enough.

        Nothing 'wrong' with a perfect gain stage or a cleaner-than-usually first gain stage, not what I wanted to imply anyway.

        Have you considered a folded cascode design and a constant current source at the top?
        No - I have not...
        “If you have integrity, nothing else matters. If you don't have integrity, nothing else matters.”
        -Alan K. Simpson, U.S. Senator, Wyoming, 1979-97

        Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

        https://sites.google.com/site/stringsandfrets/

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        • #19
          Originally posted by R.G. View Post
          Doh! I knew I was missing something! Even with the schematic right in front of me, I saw it backwards!

          So as you're using it, you are using the triode as a voltage to current converter for signals, and the current mirror is letting you convert the current back to a voltage through the resistor on the output. The output traces the tube's Vgk verus Ip line for signals.
          Exactly... with FB all around to minimize the impact of the actual device curves.
          “If you have integrity, nothing else matters. If you don't have integrity, nothing else matters.”
          -Alan K. Simpson, U.S. Senator, Wyoming, 1979-97

          Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

          https://sites.google.com/site/stringsandfrets/

          Comment

          • #20
            Originally posted by uneumann View Post
            OK - here it is... This should help. Tweak for your needs.
            Thanks. It looks like potentiometer_standard symbol is missing (it is not included in the installation of LTSpice). I wonder why two load resistors are 10Meg instead of 1Meg. Is it on purpose?

            Mark

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            • #21
              Originally posted by MarkusBass View Post
              Thanks. It looks like potentiometer_standard symbol is missing (it is not included in the installation of LTSpice). I wonder why two load resistors are 10Meg instead of 1Meg. Is it on purpose?
              Mark
              Here is the pot file... potentiometer_standard.zip
              Or just remove the pot - it's not essential - it's just a convenience to set the input level.
              The 10M resistors are hi values to minimize loading on the current mirrors. It's an alternative to the FET follower buffer.
              “If you have integrity, nothing else matters. If you don't have integrity, nothing else matters.”
              -Alan K. Simpson, U.S. Senator, Wyoming, 1979-97

              Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

              https://sites.google.com/site/stringsandfrets/

              Comment

              • #22
                Originally posted by uneumann View Post
                It also sounds very clean..."tube color" will have to be added in later stages...now the signal is 5-10v peak (stage gain is ~70-100 depending on values) with lots of headroom and very low hiss and hum...a physically small circuit (no bottle or sockets), it can be located right at the input jack,
                You know, I think you're describing a perfect FX loop return/signal level recovery stage...

                -Gnobuddy

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