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Roland Super Cube 60 Squeal Help

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  • Roland Super Cube 60 Squeal Help

    Hey Folks

    I picked up one of the 80s gray Super Cube 60 with two inputs and 7 pots. There is a normal and gain input jack. The normal input works fine. As soon as I insert a cable into the gain jack the amp emits a loud high pitch squeal.

    This is not just a schematic request but I am having a hard time finding the proper schematic and will need that to continue. Once I have a schematic I can see what the two inputs do not share.

    Thank you! MarkO

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  • #2
    I expect the ground has parted from the high gain socket.
    Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
    If you can't fix it, I probably can.

    Comment


    • #3
      Or the grounding switch of the normal jack is not closing. These are what I think is called the 'SCL' model, try this schematic: https://music-electronics-forum.com/...etch?id=922334
      Originally posted by Enzo
      I have a sign in my shop that says, "Never think up reasons not to check something."


      Comment


      • #4


        Yes SCL. Thank you for the schematic!

        So, I find that if I move the plug inserted into the gain jack, I can change the intensity of the squeal or make it gone completely.

        I guess I need to remove the jack from its board and see if I can manipulate the tabs. It is the jack with the 6 tabs connected to the board.


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        • #5
          Originally posted by misterc57 View Post
          I guess I need to remove the jack from its board and see if I can manipulate the tabs. It is the jack with the 6 tabs connected to the board.
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          Before you do that, measure the resistance from tip to ground of the normal jack, with nothing plugged in. It should be zero ohms.
          If not, the switch contact of the normal jack is either dirty or bent. Try cleaning it.
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


          Comment


          • #6
            Just got back to this. Tip to ground on normal jack was good, under 1 ohm. I removed the drive jack from the board. Could not see anything wrong, nor could I bend anything due to it being in its enclosure.

            I installed a switching jack; switch and ground lug joined and connected to the ground wire of the normal jack, tip lug connected to the board which connects to R3. I am getting a loud ground buzz when I insert a guitar cable. The switch is working properly on this jack. Wondering what I am doing wrong. Is there supposed to be a resistor included?

            Thank you!

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            Last edited by misterc57; 02-24-2022, 05:53 PM.

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            • #7
              What is the dash line in the schematic connected to this input jack? Looks like it goes to a channel switch but this model does not have a channel switch jack..

              SCL-40_60_100.pdf
              Attached Files

              Comment


              • #8
                Those are all parts of the 'Drive' jack, J2. You can't just replace it with a switching jack, it has to be an exact replacement. Like you said, it has 6 tabs. Part of the jack is the channel switch.
                Originally posted by Enzo
                I have a sign in my shop that says, "Never think up reasons not to check something."


                Comment


                • #9
                  Any suggestions on where to order a replacement jack? Thank you

                  Comment


                  • #10
                    Not sure I am going to find a replacement jack for this.

                    How about a redesign? One jack and one normal/drive toggle switch in position of the second jack.

                    Looks like we have 5 connections on the jack board.

                    #1 to ground
                    #2 to switch
                    #3 to switch
                    #4 to normal input
                    #5 to drive input

                    Switch position DRIVE sends #4 "normal" to ground
                    Switch position NORMAL sends #5 "drive" to ground

                    Not sure about # 2 and #3, which should go to ground based on the switch position.

                    Doable? Bad idea?

                    Thank you

                    Comment


                    • #11
                      Not sure, but this one looks similar: https://www.musikding.de/63mm-Stereo...ith-2-switches
                      - Own Opinions Only -

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                      • #12
                        Yes that looks similar, I wonder if they are only using one set of switch contacts in the Roland.
                        I think even a TRS jack with one normally closed switch (on sleeve?) might work. Plugging into it would lift one contact, and ring to sleeve connection due to mono plug would act as closing another switch contact.

                        Originally posted by misterc57 View Post
                        How about a redesign? One jack and one normal/drive toggle switch in position of the second jack.
                        I think you would still want to use 2 jacks, there is also some attenuation and voltage divider action due to R2,R3, and the switch in the normal jack when it is not in use.

                        As to the JK-1 parts around U2A, when using the 'normal' jack, the switch #3 contact is grounded and the #2 is open. That kills the signal to pin2 of U2A and pin3 gets the normal signal.
                        When using the 'drive' jack, the switch #2 contact is grounded and the #3 contact is open. That kills the signal to pin3 of U2A, and pin2 gets the drive signal.
                        Last edited by g1; 02-25-2022, 07:49 PM.
                        Originally posted by Enzo
                        I have a sign in my shop that says, "Never think up reasons not to check something."


                        Comment


                        • #13
                          The Roland jack has only one physical switch.

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                          • #14
                            Originally posted by Helmholtz View Post
                            Not sure, but this one looks similar: https://www.musikding.de/63mm-Stereo...ith-2-switches
                            Pin orientation does not look the same..

                            Comment


                            • #15
                              A single switch version is available from the same supplier, search the website.
                              - Own Opinions Only -

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