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  • Paraphase inverter question

    Hello,
    What's happen if I couple R4 and R5 resistors to plates with capacitors and remove C2 and tie second grid directly to the junction instead, in the circuit below, please ? The coupling caps to power tubes remains into position. Thanks




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    Just like this;

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    Last edited by catalin gramada; 08-30-2019, 02:22 PM.
    "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."

  • #2
    Originally posted by catalin gramada View Post
    What's happen if I couple R4 and R5 resistors to plates with capacitors and remove C2 and tie second grid directly to the junction
    I guess it'll work the same. But why spoil the elegant simplicity of the original circuit by adding an extra capacitor?

    Comment


    • #3
      I don't expect that R4 and R5 have the same value. Do they?
      If it still won't get loud enough, it's probably broken. - Steve Conner
      If the thing works, stop fixing it. - Enzo
      We need more chaos in music, in art... I'm here to make it. - Justin Thomas
      MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

      Comment


      • #4
        Adding a C to an existing R will create an RC-filter, you wanting to roll-off / reshape the bandwidth or something?
        ...and the Devil said: "...yes, but it's a DRY heat!"

        Comment


        • #5
          Originally posted by eschertron View Post
          I don't expect that R4 and R5 have the same value. Do they?
          Why not? I would expect the circuit to have excellent self-balancing properties.
          - Own Opinions Only -

          Comment


          • #6
            Originally posted by Helmholtz View Post
            Why not? I would expect the circuit to have excellent self-balancing properties.
            It have, already tested.
            "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."

            Comment


            • #7
              Originally posted by eschertron View Post
              I don't expect that R4 and R5 have the same value. Do they?
              The same value is close enough. For perfect balance using a 12AX7 R5 should be about 2% bigger than R4

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              • #8
                Originally posted by Helmholtz View Post
                Why not? I would expect the circuit to have excellent self-balancing properties.
                All right, I was thinking that like a conventional paraphase, there's a voltage division. But I see this is a little different.
                I see that a voltage will develop at the node of R4 and R5 only when the voltages at the plates are not exactly equal in magnitude and opposite in phase. An error signal. But with "perfect symmetry" the voltage is zero, and then the voltage reaching the plate is zero... I still find myself wanting the resistors to be unbalanced in order to generate a drive signal to the grid that nets an ideal opposite plate voltage.

                edit: I see Dave has put a number on my vague itch. Thanks!
                If it still won't get loud enough, it's probably broken. - Steve Conner
                If the thing works, stop fixing it. - Enzo
                We need more chaos in music, in art... I'm here to make it. - Justin Thomas
                MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

                Comment


                • #9
                  But with "perfect symmetry" the voltage is zero, and then the voltage reaching the plate is zero.
                  The second triode will still be driven from its cathode input, even if grid signal is zero.
                  - Own Opinions Only -

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                  • #10
                    Interesting materials about circuit

                    The See-Saw circuit - A self balancing phase splitter (5).pdf

                    and different ways of thinking about nfb aplication

                    150_UL_6V6s (5).pdf
                    "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."

                    Comment


                    • #11
                      Originally posted by Helmholtz View Post
                      The second triode will still be driven from its cathode input, even if grid signal is zero.
                      True. But even that depends on a signal that is not balanced; if the cathode currents are opposite and equal then there's no cathode voltage deviation to drive a signal. If the grid error signal is doing its job then the cathode deviation should be minimal.

                      But I confess, there are more servo loops than what I initially thought.
                      If it still won't get loud enough, it's probably broken. - Steve Conner
                      If the thing works, stop fixing it. - Enzo
                      We need more chaos in music, in art... I'm here to make it. - Justin Thomas
                      MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

                      Comment


                      • #12
                        Originally posted by catalin gramada View Post
                        Interesting materials about circuit
                        I like
                        And in the example, the cathode is bypassed.
                        If it still won't get loud enough, it's probably broken. - Steve Conner
                        If the thing works, stop fixing it. - Enzo
                        We need more chaos in music, in art... I'm here to make it. - Justin Thomas
                        MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

                        Comment


                        • #13
                          Originally posted by catalin gramada View Post
                          Interesting materials about circuit

                          [ATTACH]54954[/ATTACH]
                          That paper lost me
                          I simply calculated the open loop gain (A) of a 12AX7 driving a 1M resistor and put that in the NFB equation.

                          A = uRL/(RL+ra) = 100*90/(90+62) = 59

                          G = A/(1+AB) where B is the feedback factor (1 in this case)
                          G = 59/(1+59) = 0.98

                          Closed loop gain G should be 1 for perfect balance therefore the feedback resistor should be 2% bigger.

                          Comment


                          • #14
                            What does simulation say? Any difference with bypassed cathode resistor?
                            - Own Opinions Only -

                            Comment


                            • #15
                              Originally posted by Helmholtz View Post
                              What does simulation say? Any difference with bypassed cathode resistor?
                              I suspect not but I'll check it out after I get another beer

                              Comment

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