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KC350 - Blown Amp? Preamp Seams OK

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  • #16
    If I recall, this should be a low cost diaphragm to repair the tweeter. Do measure the voice coil first and verify it is 1". It's a pretty standard diaphragm that's used in lots of similar tweets.
    "Yeah, well, you know, that's just, like, your opinion, man."


    • #17
      I ended up just ordering a pair of replacement drivers from Parts Express:
      Horn: 270-055
      Woofer: 290-408 Eminence Beta 12A

      I did pull the stock 12" driver apart late last night before ordering, very carefully with a heat gun to loosen the glue with the hopes that I'd be able to re-wrap the VC, but about half of it was very burnt and the surround plastic was melted and deformed.

      Once I get them and install them, I'll report back. I'm hopeful I'll have a functional amp for about $110 all in.


      • #18
        Did we ever determine if the stock tweeter was a piezo or a dynamic? Is there a crossover?
        Education is what you're left with after you have forgotten what you have learned.


        • #19
          There is a basic first order crossover (C18 is a 1.5uf/250v cap on the Tweeter only), which I believe is a dynamic driver. I believe that's a really high crossover ~9kHz range, but 1st order that's less of a big deal.


          • #20
            The KC-350 uses a real driver tweeter (not a piezo).
            Here is a cabinet schematic:

            roland_kc-350 enclosure.pdf

            And the parts list:

            roland_kc-350 Parts.pdf
            Last edited by Jazz P Bass; 03-15-2017, 12:33 AM.


            • #21
              I think the KC-550 uses the standard Foster type diaphragm but I don't think the KC-350 does? They are different tweeters.
              "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


              • #22
                Yeah. I think the KC 350 uses a 3 1/2 driver.

                The KC 550 uses a 4 1/4.

                I know the KC 60 uses a piezo.
                Last edited by Jazz P Bass; 03-15-2017, 01:08 AM.


                • #23
                  alive and kicking

                  sorry to raise this from the dead, working on a kc-350 in my shop and took all the same measurements as this guy but found different result on a few transistors,can anybody point me in the right direction to find out how to bring her alive again?

                  Originally posted by Jung4g View Post
                  Ok, finally got some time in the shop again.

                  Here's the results from the requested transistors with common lead (black) first:


                  That looks good to me, but I could be off.

                  1) Are the other channels working? I never got to test as what I had available before pulling it apart would work, but the speakers were blown anyway
                  2) The first thing i do is always verify you have all of your voltage rails working I believe the PS is ok, I was getting +/- 54-55V with no load and +/- 15V to the preamp
                  3) If you suspect the original owner plugged in a hot signal into the Aux input, I would replace IC 6 Ok, so grab a new pair of the M5218AL Op Amps
                  4) It would be help full if you had a signal generator. Before I could afford mine, I downloaded one from the Android playstore on my phone, cut an 1/8" aux cable in
                  half and made a simple and cheap signal generator! Hey it works! Easy enough to make. I've got a app that outputs any frequency I want for tuning Home Theater Crossovers, until the amp works, I don't know where I'd use that
                  5) Check your main output transistors using a multimeter in diode mode Done, results above

                  Next Steps?


                  • #24
                    New amp -> new problems -> start a new thread to avoid confusion.

                    You made the measurements so lead the new thread with your results.
                    Experience is something you get, just after you really needed it.