Korg Polysix synthesizer

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  • Agent24
    I see dead caps
    • Oct 2007
    • 4951
    • New Zealand

    #101
    Re: Korg Polysix synthesizer

    Yeah you're better off staying with the same value or a little higher. It's not good practice to reduce capacitance unless you test and measure the system thoroughly and find it doesn't make a difference.

    You don't want to go chasing another non-existent fault later on because you used capacitors that were too small. If the larger, paralleled ones fit, just use those.
    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
    -David VanHorn

    Comment

    • SteveNielsen
      Retired Tech
      • Jun 2012
      • 2327
      • USA

      #102
      Re: Korg Polysix synthesizer

      Oh I'm not leaving it like that, it was just a test while I've got the board out and it got me wondering why they used such high cap values in the 1st place, most linear PSUs I've seen don't use anywhere near that high of capacitance in the rectifier filtering. I thought the capacitance was selected mostly based on the ripple frequency and the circuit impedance.

      For checking out how the PSU does hooked up to the rest of the boards I will revert back to the stacked caps as you advise, but no they won't quite fit with the case closed unless I string them off to the side somehow. I will replace them with the proper parts once I obtain them (which will be a while unless I happen to salvage some good ones).

      Comment

      • stj
        Great Sage 齊天大聖
        • Dec 2009
        • 30997
        • Albion

        #103
        Re: Korg Polysix synthesizer

        i suspect that the load will be all over the place once the cpu starts sequencing stuff through all those op-amps.

        i dont know how much current those use, but they often run pretty warm!

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 30997
          • Albion

          #104
          Re: Korg Polysix synthesizer

          btw, do you have a rotary-encoder in your spares box?

          Comment

          • SteveNielsen
            Retired Tech
            • Jun 2012
            • 2327
            • USA

            #105
            Re: Korg Polysix synthesizer

            Yeah, and there's a metric butt-load of op-amps in this thing.

            No, I'm afraid I don't have a rotary encoder unless there's one inside of something in my pile of junk I haven't operated on yet. What would have one?

            Comment

            • stj
              Great Sage 齊天大聖
              • Dec 2009
              • 30997
              • Albion

              #106
              Re: Korg Polysix synthesizer

              anything wih a rotary control that just keeps turning.

              i'm asking because you can add one to your component tester to use extra menu's / functions in the new software.

              Comment

              • SteveNielsen
                Retired Tech
                • Jun 2012
                • 2327
                • USA

                #107
                Re: Korg Polysix synthesizer

                Haha! I know, you want to get back to the tester! I do too! I have to wait and see if I can buy the chip and programmer for that, and that'll be a bit, I get $$ tomorrow, then ordering and waiting. You mean a rotary switch? I think I've got one somewhere. If not, please elaborate.

                Comment

                • stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 30997
                  • Albion

                  #108
                  Re: Korg Polysix synthesizer

                  not exactly a rotary switch - not in the traditional sense.

                  it has 2 outputs, and lots - usually 10-50 clicks per revolution.
                  it switches the 2 outputs in sequence as you turn it - the sequence indicates the direction it's turning.
                  you sometimes find them used as digital volume controls or channel selectors.

                  Comment

                  • SteveNielsen
                    Retired Tech
                    • Jun 2012
                    • 2327
                    • USA

                    #109
                    Re: Korg Polysix synthesizer

                    I see. I haven't got one that I know of but I've issued myself a BOLO for one.

                    Comment

                    • stj
                      Great Sage 齊天大聖
                      • Dec 2009
                      • 30997
                      • Albion

                      #110
                      Re: Korg Polysix synthesizer

                      some car stereo's and mini hifi's use them.

                      Comment

                      • SteveNielsen
                        Retired Tech
                        • Jun 2012
                        • 2327
                        • USA

                        #111
                        Re: Korg Polysix synthesizer

                        Back to the Korg... I have some concern about the stacked caps I'm using for C13 fitting with the case closed. I do have another 6800uF 56v cap I could use in its place and save some space but I've already bumped C13 from 2200uF to 2700uF. Is using the 6800uF for C13 out of the question?

                        Comment

                        • stj
                          Great Sage 齊天大聖
                          • Dec 2009
                          • 30997
                          • Albion

                          #112
                          Re: Korg Polysix synthesizer

                          go for it

                          Comment

                          • SteveNielsen
                            Retired Tech
                            • Jun 2012
                            • 2327
                            • USA

                            #113
                            Re: Korg Polysix synthesizer

                            I did and it appears to work fine with and without loads on +15 & -15 outputs. I read 7~8mV AC ripple on all outputs either with or without a load. All voltages are within the tights specs. I believe it will all fit now but I'm gonna tack the caps down with some hot glue. They're a bit mobile and the trace pads on this old board don't take kindly movement of parts. Then I'll have to do some reassembling and see if the whole synth works now.

                            Comment

                            • SteveNielsen
                              Retired Tech
                              • Jun 2012
                              • 2327
                              • USA

                              #114
                              Re: Korg Polysix synthesizer

                              Well, I'm gonna table this project. The PSU works fine and is within specs however there is a lot more wrong with this thing than I am capable of dealing with at this time without a scope, and I need to make room in my small work area for something else.

                              Comment

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