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  • 770 Crossover

    Hello all,

    I'm trying to modify my 770 using the MIG-LR.

    When I went to do it, I noticed that the crossover board is different to the one displayed in both the 770 manual and the MIG-LR installation manual.

    I proceeded to do the modification, as all the necessary components for connection were present on the board. I am getting signal, but unfortunately it is extremely quiet, even with all volumes and drawbars pinned.

    Was there an earlier version of the 770? Or maybe a previous owner has swapped in a board from a different model Leslie?

    I've attached some pics.

    Any help would be greatly appreciated.

    P

    Click image for larger version

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    Hammond - S-6, M-3, L-122, A-100
    Yamaha - YC-45D w/ RA-100, DK-40CI, D-85, E-75, C605
    Eminent - 310 Unique
    Estey - Folding Reed Organ

  • #2
    Originally posted by Phathead View Post

    I'm trying to modify my 770 using the MIG-LR.

    [ATTACH=CONFIG]29805[/ATTACH]
    You want to turn it into a russian jet ?

    I do not know what this additional plate do.
    There are logic circuits and a relay.
    At the place where there was a capacitor, We have 2 white threads that derivates the sound from the Master Vol Ctrl.
    May be a silent module ?

    I will remove all this and put the capacitor back in its place.

    JP

    Comment


    • #3
      I've worked on a lot of Leslie 760s, and I've never seen that additional circuit board before. I have no idea what it does.

      Like JP says, if it doesn't work correctly, I would remove anything unknown.
      I'm David. 'Dave' is someone else's name.

      Comment


      • #4
        Russian Jet! :D This is the well-known Mig-LR tube conversion for solid state leslies. https://www.keyboardpartner.de/hammo...MIG-LRII-e.pdf

        There wasn't an earlier 770, as far as I know, but the first two leslies in this class were the '760 Walnut' and '760 Black'. The 760 Walnut became the 770 and the 760 Black was replaced by the Pro-Line 760. It's possible that the earlier ones had different boards - try to locate a 760 manual and see if there are any differences. Captain Foldback's pages may have one.

        But in any case all you're doing is taking that signal from immediately after the input gain pot, so it shouldn't be too tricky to find the correct place to do this even if the boards are slightly different.
        It's not what you play. It's not how you play. It's the fact that you're playing that counts.

        New website now live - www.andrew-gilbert.com

        Current instruments: Roland Atelier AT900 Platinum Edition, Yamaha Genos, Yamaha PSR-S970, Kawai K1m
        Retired Organs: Lots! Kawai SR6 x 2, Hammond L122, T402, T500 x 2, X5. Conn Martinique and 652. Gulbransen 2102 Pacemaker. Kimball Temptation.
        Retired Leslies, 147, 145 x 2, 760 x 2, 710, 415 x 2.
        Retired synths: Korg 700, Roland SH1000, Jen Superstringer, Kawai S100F, Kawai S100P, Kawai K1

        Comment


        • #5
          Thanks for all the responses so far!

          I should have explained my photos. The first is of the board before modification. The second is after.

          No luck scouring the other schematics yet Andy, but thanks for the suggestion and for giving clarity. I'll keep searching.

          I realized tonight that I had mixed up "out" from the tube stage and "ground". Corrected the wiring and the problem persists exactly as before. Hopefully I didn't damage any components by having them switched!

          I'm in contact with the guy that sold me the upgrade. He's helping me troubleshoot. I'll update the thread as things progress.
          Hammond - S-6, M-3, L-122, A-100
          Yamaha - YC-45D w/ RA-100, DK-40CI, D-85, E-75, C605
          Eminent - 310 Unique
          Estey - Folding Reed Organ

          Comment


          • #6
            Thanks andy for the secret drawings of this russian jet.

            It's more look like a distorsin pedal than a jet.

            It is not very complicated.

            The 1SH 18b tube distord the sound. It is a very low voltage pentode with direct heating.
            Leave this aside for the moment and directely go to the switch U2 that bypass this stage.

            The logical circuits U2 (and U3) are 5 volts powered.
            U2 4066 is the fonction switch controled by Remote (PL5) and Mute (PL4)

            PL5 to Gnd (0 Volts) = Direct way (Bypass - No distorsion)
            PL5 Open (5 Volts) = Tube way (Sound distorded)

            PL4 to Gnd (0 Volts) = Mute (No Sound)
            PL4 Open (5 Volts) = Sound distorded or not. See PL5.

            The first thing to do is to verify if this controls works.
            I do not know why PL5 and PL4 are wired but there may be a problem here as well as if the module is not powered (PL3 = GND / PL6 = + 28V)

            Mixed up "out" from the tube stage and "ground" may not damage anything. Simply the module was not powered.

            JP
            Last edited by Jyvoipabo; 05-25-2018, 09:03 AM.

            Comment


            • #7
              Thanks for weighing in JP! I have an update.

              I managed to achieve full volume by isolating the board from the back panel using nylon standoffs and rubber washers. Unfortunately, the Master Volume pot stopped working due to not being grounded! I'm going to try and wire the pot directly to ground. Hopefully it works. Any other suggestions are welcome!

              Thanks,

              Paul
              Hammond - S-6, M-3, L-122, A-100
              Yamaha - YC-45D w/ RA-100, DK-40CI, D-85, E-75, C605
              Eminent - 310 Unique
              Estey - Folding Reed Organ

              Comment


              • #8
                I wasn't able to find a way to ground the pot without causing the volume drop. Definitely a pickle.
                Hammond - S-6, M-3, L-122, A-100
                Yamaha - YC-45D w/ RA-100, DK-40CI, D-85, E-75, C605
                Eminent - 310 Unique
                Estey - Folding Reed Organ

                Comment


                • #9
                  Hello,

                  Martyrized Master volume is a recurrent problem.
                  Here's how I solved it on a 760 :

                  I open wide the frame to accesss easily the amphenol plug and the new Master Vol with knob moved from PCB

                  JP

                  Comment


                  • #10
                    I can't see the image unfortunately. Are you able to re-upload?

                    I'd love to know more details about how you solved this problem. I don't quite understand yet.
                    Hammond - S-6, M-3, L-122, A-100
                    Yamaha - YC-45D w/ RA-100, DK-40CI, D-85, E-75, C605
                    Eminent - 310 Unique
                    Estey - Folding Reed Organ

                    Comment


                    • #11
                      I understand. Don't worry, you will be able to solve this problem later.

                      If you have a preamp, the volume control of the pedal will be sufficient.
                      In any case you can discard temporary this control :
                      Disconnect the arrival of the sound on the filter (Red lug)
                      Connect it directly to the input of your module.

                      And, decrease also bass and treble controls to 25% approx to protect speakers against a loud 'Honk'.

                      JP

                      Comment

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