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Peavey Centurion no Auto mix input

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  • Peavey Centurion no Auto mix input

    So, A and B inputs for both channels work fine, the auto mix input does not.

    Got the schematic from here, and on the one I have, the tip and ring of the auto mix input are grounded by the ch1 and ch 2 A and B inputs.


    i checked the components connected to that input, no shorts from them.

    The LED's light up when a jack is plugged into the auto mix input.

    No way it can function if the jack is grounded. The jacks are stock, unless something is bent inside or Peavey used the wrong jacks when it was built.

    Or am I missing something?
    Attached Files

  • #2
    Are you using a footswitch with it?

    Comment


    • #3
      Try it with a T R S plug and the Ring not connected. If the Ring is ground there will be no change for the indicator switching transistors.
      The Tip connects to both inputs and there is no reason, save broken sockets, that is won't work on paper.
      Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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      • #4
        Automix ring is shown grounded. Tip should go to switch contacts of A & B inputs.
        If yours is stock and not like that, maybe there is a different schematic.
        "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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        • #5
          Circuit looks the same as the schematic

          But, as mentioned, A & B inputs 1 & 2 are grounded with switching jacks.

          Not using a footswitch

          Weird.

          Comment


          • #6
            Originally posted by drewl View Post

            But, as mentioned, A & B inputs 1 & 2 are grounded with switching jacks.
            They only ground via switch of automix tip. As soon as a cord is (fully) in automix jack, they should not be grounded.

            Are they board mounted jacks, or wired?
            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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            • #7
              Originally posted by drewl View Post

              But, as mentioned, A & B inputs 1 & 2 are grounded with switching jacks.

              Weird.
              A&B inputs are grounded via the automix switching jack. So inserting a plug there should lift the ground for the inputs.
              Last edited by Helmholtz; 04-18-2022, 04:48 PM.
              - Own Opinions Only -

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              • #8
                There are two switched contacts in the Auto jack. Your LEDs come on when you plug in so that contact is working. That leaves the signal path contact.

                the tip and ring of the auto mix input are grounded by the ch1 and ch 2 A and B inputs
                You have that backwards. The channel 1 and 2 input jacks are grounded through the Automix jack. Plugging into the automix should connect the guitar signal to both channel inputs. Stick a signal in there and follow it with a scope or tracer over to each input channel jack.

                Why are we using the schematic for a Bass Mk3?

                Attached Files
                Education is what you're left with after you have forgotten what you have learned.

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                • #9
                  Originally posted by Enzo View Post
                  Why are we using the schematic for a Bass Mk3?
                  That Centurion file you linked is another 'invalid'.

                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                  Comment


                  • #10
                    Why don't they ever like my files? Are they THAT old?

                    Try this

                    Attached Files
                    Education is what you're left with after you have forgotten what you have learned.

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                    • #11
                      Originally posted by Enzo View Post
                      There are two switched contacts in the Auto jack. Your LEDs come on when you plug in so that contact is working. That leaves the signal path contact.



                      You have that backwards. The channel 1 and 2 input jacks are grounded through the Automix jack. Plugging into the automix should connect the guitar signal to both channel inputs. Stick a signal in there and follow it with a scope or tracer over to each input channel jack.

                      Why are we using the schematic for a Bass Mk3?
                      Yes, on the schematic.
                      Looks like I had the Bass version, but the inputs are the same, Anyway:

                      On this preamp board, Ch1 & 2 A & B inputs are four connector jacks, with the tip of all four grounded, thus grounding the tip of the auto mix input.

                      These are pc board mounted jacks, and looking at some of the connections that were never touched, look to be original.
                      I'll take a pic and show you when I get home from work.

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                      • #12
                        I maintain my case. Look at the schematic. Look at the four channel input jacks. Where is there a ground connection? The ground connection is through the automix jack. Remove teh automix jack and the inputs are not grounded. The four input jacks have grounded bushings, but no grounded tip contact.

                        It is a clever circuit. If you plug into either channel in, the other channel remains grounded via the automix. If you plug into the automix, that common trace that was used for grounding becomes a common signal trace to split the signal into the two channels.

                        On the Bass layout, you can see the traces from the two input jacks connecting to the cutout on the automix.
                        Education is what you're left with after you have forgotten what you have learned.

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                        • #13
                          See post 7. Plugging into the automix jack removes the grounding of all inputs and routes the signal to A and B channels.
                          - Own Opinions Only -

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                          • #14
                            Yes, I see the way it's SUPPOSED to be.

                            Now picture the four jacks being four pin with the switch grounding the tip of all four input jacks also grounding the auto mix.

                            That is how this amp is set up.

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                            • #15
                              We'll see if you can make out the picture.

                              I labeled the A jacks of channel one and two and you can see how they ground the auto mix jack.

                              If I plug a cord into A jacks of both channels it lifts the ground of the auto mix jack.

                              I need to remove them and take out the switch connector of both.
                              Attached Files

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