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Leslie 925 Project and Amplifier Question

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  • Leslie 925 Project and Amplifier Question

    Greetings to the Forum Experts

    My latest Leslie project is stuffing a Leslie 925 into a Leslie 330 cabinet with the addition of 925's upper horn cabinet (yes, a second horn) which will sit on top of the 330. The horns are counter rotating, the second horn being driven by the 925's auxiliary channel.

    The problem is with the 925 amp/power supply. When the speakers were first connected, there was an overpowering hum coming from all three which were unaffected by volume changes in the TrekII combo preamp. So, after inspecting the circuit boards, I saw that the capacitor C63 had snapped off the circuit board of the power supply. See figure 9 on page nine of the document (or page 11/21 of the pdf file). That cap was replaced an now there is now sound... hum or otherwise.

    http://www.synthfool.com/docs/Leslie...ice_manual.pdf

    So, I am writing to ask the experts here in the Forum to point me in the right direction on how to get the amp/power functional again. Many thanks to those who are so generous with their time and talents! Photos will be uploaded soon.

    One other request... does anyone know the the size/measurements of the T-molding used on the Leslie 330 cabinet? Where might I find this part?

    Best!

    Dan D.
    Last edited by dannicdem; 07-11-2018, 02:18 PM. Reason: Clarify Description of Problem
    Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
    Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
    Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
    Lowry GAK25 & GAK
    Farfisa Combo Compact

  • #2
    Greetings to you,

    See page 8 : C63 is involved in the brake circuit. It have no link with the hum.

    May be there is a problem with an amplifier.
    I suggest : Disconnect all the speakers and let the amplifier warm up while cheking the temperature of the output transistors.
    It may be necessary to remove the plastic covers. No dangerous voltage inside. You can hold your finger on the case without pain.

    Then reconnect the speakers one by one and try to identify the channel with problem.

    JP

    Comment


    • #3
      Yes, conducted the 'finger on the transistor' test and all six were fine and touchable. Also reconnected the speakers however there still is no sound. What next?

      Thanks to the experts for their time and sharing.

      Best!

      Dan D.
      Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
      Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
      Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
      Lowry GAK25 & GAK
      Farfisa Combo Compact

      Comment


      • #4
        If there is no over heat, and if there is not a loud 'honk' at power up, then you have no serious problem in the power amps.
        Mais s'il vous plait clarifiez :
        What is the problem : Hum or no sound ?
        Are the controls turned full clockwise ?

        JP

        Comment


        • #5
          The problem is no sound. All pots are turned up fully.

          Best!

          Dan D.
          Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
          Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
          Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
          Lowry GAK25 & GAK
          Farfisa Combo Compact

          Comment


          • #6
            I understand,
            Before there was hum, now there is no sound at all.

            The most likely explanation is a failed amplifier that has blown the fuse boring of excessive consumption.

            For this reason, it is prudent to disconnect the connectors P10, P11, P12 prior replacing the fuse.

            Then, check +33V and -33V is present on the power supply with a meter.
            At this point the speed control should work.

            Reconnect the amps one by one and try to identify the one that hums.

            JP

            Comment


            • #7
              Thank you for your continued expert assistance. To restate the problem: A hum was coming from all three speakers. The hum was unaffected by volume changes in the TrekII combo preamp.

              The fuse in not blown. Speed switching works perfect including the brake function.

              As I am lacking in technical knowledge, can you provide step-by-step instruction on how to check the power supply. I do have a digital meter!

              Thank you so much for your time and knowledge!!!

              Dan D.
              Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
              Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
              Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
              Lowry GAK25 & GAK
              Farfisa Combo Compact

              Comment


              • #8
                I complete :
                There is no overheating of the power transistors and not a loud 'honk' at power up.
                Your amp is healthy at 80%.
                I think you may have a problem with the cable or the pedal. Check the cable carefully looking for a broken lug.

                Anyway, disconnect inputs of the pedal and continue the check up of the amp.

                On the cross-over board there is a master volume control.
                Does it have an action on hum?

                If yes set it to zero and as you have a voltmetre. Connect - to the ground.
                Check the supply voltages + 33V, -33V, + 28V (+/- 10%)
                And output voltage of amps (Points R and H) = 0V (+/- 0.2V).
                These values are significant to the condition of the unit.

                JP
                Last edited by Jyvoipabo; 07-16-2018, 12:27 AM.

                Comment


                • #9
                  Can you please tell me exactly where to make the connections for the voltage checks.

                  Sorry, I am not knowledgeable in this area and ask for me specific instruction/details.

                  Dan D.
                  Last edited by dannicdem; 07-16-2018, 07:22 AM.
                  Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
                  Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
                  Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
                  Lowry GAK25 & GAK
                  Farfisa Combo Compact

                  Comment


                  • #10
                    Hello,

                    If you do not know how to measure the voltage, it is a long way to learn without making mistakes having sometimes heavy consequences.

                    So if the master volume control varies the hum, then forget it. Your amp is 99% healthy.

                    Check Amphenol sockets. Move it gently. Pull each wire looking for a broken pin.
                    It can be also a ground loop if both the organ and the pedal are grounded.

                    JP

                    Comment


                    • #11
                      Thank you for the continued support! I have checked the 9 pin cable and even tested with another 9 pin cable, the cable and pins are fine. I have used a meter on many amps in my Leslie/Hammond ventures with complete confidence, let's not limit the the repair efforts.

                      Are there any other experts who can assist with my efforts to repair the Leslie 925 amp/power supply?

                      Best!

                      Dan D.
                      Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
                      Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
                      Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
                      Lowry GAK25 & GAK
                      Farfisa Combo Compact

                      Comment


                      • #12
                        I restored a 925 and the amp had a couple issues so I sent it to Capt. Foldback http://www.captain-foldback.com/service/ He went through it quickly, found a couple of bad parts and replaced them, and gave it a clean bill of health. It is a great sounding solid state amp when its right.
                        There's at least 200 things between the power supply and the speakers that can be causing the problem...I try to fix whatever I can, but when it comes to un soldering a bunch of components to check their condition out of circuit and going after test points...I don't have that kind of patience anymore. The Leslie is a very simple amp..everything you need to troubleshoot it is in the doc. you included. It's easy to find the test points and the voltages that are supposed to be there...but...you have to know what is causing the voltages to be wrong...I don't go there.
                        I bought T-molding from http://www.outwater.com/home/index.cfm the original style isn't made anymore, I used a slightly wider molding and it worked out better as far as framing the grill cloth.
                        Hope this helps...good luck!
                        Attached Files
                        1963 C-3 147 Leslie
                        1972 X-77GT 2 - 77P Leslie
                        Kurzweil K 2000

                        Comment


                        • #13
                          Hi Tim

                          Thanks for the wealth of information. A note is on the way to the Captain. BTW, the grill work and handle addition is top shelf! Can you tell me which parts (dimensions) you ordered?

                          Best!

                          Dan D.
                          Leslie 31H Type 2 x2, 45 x2, 251, 351, 720, 710 x3, 700, 2101, 925, 860, 700, 330, 120 x2, 104, 25, 125 x2
                          Hammond Concorde 2312M, Hammond Elegante 304100, Hammond A-100, Hammond C2
                          Nord Electro 4D & 5D, Kawai MP6, Ensoniq ESQ &Mirage, Wurlitzer Electric Piano 200
                          Lowry GAK25 & GAK
                          Farfisa Combo Compact

                          Comment


                          • #14
                            Thanks! I believe I used 3/4" black T-molding for the grill edges, the grill cloth is the standard black amplifier grill material. The handles come from http://www.tchweb.com/tchstore/home.do
                            1963 C-3 147 Leslie
                            1972 X-77GT 2 - 77P Leslie
                            Kurzweil K 2000

                            Comment

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