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15 position rotary encoder?

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  • 15 position rotary encoder?

    Looking for a source for an Alpha B50k 15-position. I'm assuming this is what is called a rotary encoder? Looks to be a 9mm (green case).


  • #2
    Have a pic? What's it out of?


    • #3
      An encoder would not normally have a resistance value. Sounds more like you have a 50k pot with detents. Those you find in volume control applications. Seems to me Trace Elliot amps used detented volume controls for a while. Pointless in my view.

      Oh and some earlier Peavey power amps like the CS900 used detented volume controls - 50k too, I think.

      Encoders usually rotate continuously. That is to say there is no all the way up or down, the thing spins all the way around. And if it has three pins like a pot, usually the center will be the common, and as you turn the contol, the thing acts like a switch, just off or on between pins, no variable resistance.

      So answer pecorps questions.
      Education is what you're left with after you have forgotten what you have learned.


      • #4
        Its on the effects section of an Alesis X Guitar. It selects one of 15 effects to modify. It looks like a standard 3-pin pcb mount pot, and B50k is stamped on the side of it. Looks almost identical to the 9mm pot I replaced on a marshal compression pedal.

        **Actually this would be a 16 position. I was counting detents and forgot to count the first position.***
        Last edited by ricach; 03-27-2011, 07:42 PM.


        • #5
          Sounds like the MCU is using it's analog to digital hardware to select which program to modify based on the voltage of a pin. If you sub in a standard pot and it works, that's what you have. If you can't find that particular pot, a rotary switch with resistors will work, but it'll be big and expensive.


          • #6
            Didn't Tube Works use detent pots?
            B50K sounds like a common gain pot.
            Contact Genz-Benz & see if they can help you out.
            (measure the lead length if you can. They have a short & a long one)
            Contact info:


            • #7
              Tack three wires to the pc board and use them as test points. Now use clip wires and take ANY 50k pot, and clip it into the circuit. That will tell you quickly if it wants a pot or an encoder. And if your bad part has any of its function left, you should be able to tell with a meter if it was a pot or not. For than matter, if replacement is certain, then take the old one apart and see what is inside.

              And I would think a 50kB would be about the easiest pot to find in any size.
              Education is what you're left with after you have forgotten what you have learned.


              • #8
                Thanks everyone for your help so far. I do intend to disassamble, but with the hope of cleaning/repairing the pot. In my search I've come across a fantastic site for parts - the volume of Alesis parts are staggering alone, not to mention they carry specific parts for many manufacturers .
                Instrumental Parts - Numark Parts , Alesis Parts , Technics Parts , Pioneer CDJ Parts and More

                The pot has only 3 leads, so with Gray encoding, that's only 8 possible selections modes, so this is not a rotary encoder.


                • #9
                  There are numerous types of decoder. One is the absolute position encoder, meaning that each position has its own code output. That is what you describe. But mostly what we see in our stuff is just plain old decoders. There is a common center leg, then the other two legs alternate hi-lo in quadrature. Up-up-down-down-up-up... The system uses this pattern to determine how far you turn and what direction.

                  The two sides are offset, one closes before the other. Turning one direction versus the other means one of them closes first. SO it boils down to one side is the direction and the other side pulses movement. This is how the up/down data wheels work. No matter where you move the thing to withpower off, it never confuses it.

                  None of this matters if it is a pot, of course.
                  Education is what you're left with after you have forgotten what you have learned.


                  • #10
                    Alesis used a bizarre kind of encoder on their Ion synth. They were endless pots with two wipers.

                    However I bet this is just a regular 50k pot with detents.
                    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"


                    • #11
                      Yeah well,Alesis also made some 16 channel mixers where all the controls were printed on the circuit board. The knobs with wipers were captive to the upper panel. Good luck cleaning that or replacing a bad pot. And even more than that, explaining it to the customer who needs a pot, "replaced."
                      Education is what you're left with after you have forgotten what you have learned.


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