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Unknown Subwoofer Power Amplifier Issue (Loud Buzz Has Developed)

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  • Unknown Subwoofer Power Amplifier Issue (Loud Buzz Has Developed)

    Hi there. I'm REALLY hoping I can get some assistance here. I figured this would be the best forum since I BELIEVE that the subwoofer I have was built from a kit here at Parts Express about 11 years ago. I've had this "Subwoofer Kit" assembled and running amazingly for the past 11 years. Over the past few weeks, however, this has started to change. I suddenly noticed a slight, low level buzz that was starting to grow louder. Finally, about two days ago, that buzz got too loud for me to tolerate anymore. If the subwoofer is plugged into the wall and powered on, or on auto, a loud buzz will come out of the subwoofer. If I disconnect the line level input to the subwoofer, the buzz grows super loud.

    Wondering if a ground loop suddenly formed out of nowhere, I attempted to plug the subwoofer into different outlets, and even using an isolation transformer, and nothing. Having worked on electronics for years and having rebuilt numerous CRT monitor chassis, I have a feeling that something in the power supply section has gone bad. I can't tell if this is a transistor or a capacitor that may have gone foul. Most frustrating is that I cannot tell who the manufacturer of this subwoofer kit is, so I can't just go and get a replacement. (Which I would certainly do if it's not too expensive. If a replacement panel for my subwoofer is too costly, then just replacing the faulty component is something I can easily do).

    I've attached photos I took of the panel just in case anybody has any idea what this is, or what I can do to eliminate this obnoxious buzz that just developed over the past couple of weeks. Many thanks!
    Power Supply Section Back Panel (interior) Back Panel (exterior)

  • #2
    That is a Keiga amplifier. Just like the old PE 250W and the ApexJr 'Apex Senior' amplifier.

    Later,
    Wolf
    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

    *InDIYana event website*

    Photobucket pages:
    http://photobucket.com/Wolf-Speakers_and_more

    My blog/writeups/thoughts here at PE:
    http://techtalk.parts-express.com/blog.php?u=4102

    Comment


    • #3
      Oh thank you so much Wolf. This should help me search down the issue and get it fixed. It was just finding what part it was that has holding me up. Much appreciated!

      Comment


      • #4
        If you don't mind me asking, is there a direct drop in replacement for this one? I'm just trying to decide if I'd be better off trying to fix this busted amp, or just spend the dollars and order a brand new one?

        Comment


        • #5
          The PE model is NLA, but the other company's 'Apex Senior' will drop in, and is still available. Being a competitor, I cannot post a link, but you should be able to find it.

          Later,
          Wolf
          "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
          "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
          "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
          "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

          *InDIYana event website*

          Photobucket pages:
          http://photobucket.com/Wolf-Speakers_and_more

          My blog/writeups/thoughts here at PE:
          http://techtalk.parts-express.com/blog.php?u=4102

          Comment


          • #6
            Once again, many, many thanks kind sir.

            Comment


            • #7
              I had the same issue with a Polk sub and it turned out to be a dud capacitor

              Geoff

              Comment


              • #8
                Yeah. Looking at the cost, it'll be cheaper for me to just replace all the capacitors in there. Looking at the brands and ratings, these are junk. However, how freaking long does it take for the capacitors on these things to drain after unplugging it from the wall? Good lord. I unplugged the subwoofer for a good 36 hours, and upon trying to remove the filter caps in the power supply section, they both violently exploded. Wow.

                I think I'm going to let this sit for a week or so now to let any remaining charge in there bleed out. I might have to test a bunch of components on there now due to the unexpected discharge.

                Comment


                • #9
                  You SHOULD be able to "bleed off" ANY (or all) caps by jumpering across each one w/a resistor - not sure of the value, but maybe a 20ohm 2 watter. ("Guess" is really out-of-the-blue. I'd go higher wattage if you go even lower in impedance?) I would NOT expect a cap to explode upon discharge though, just overvoltage?

                  Comment


                  • #10
                    I don't recall if those amplifiers have bleeder resistors or not, but for safety they really should. It's possible they were past their prime if they blew up that easily.

                    Later,
                    Wolf
                    "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
                    "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
                    "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
                    "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

                    *InDIYana event website*

                    Photobucket pages:
                    http://photobucket.com/Wolf-Speakers_and_more

                    My blog/writeups/thoughts here at PE:
                    http://techtalk.parts-express.com/blog.php?u=4102

                    Comment


                    • #11
                      Originally posted by Jdurgi View Post
                      ... However, how freaking long does it take for the capacitors on these things to drain after unplugging it from the wall? ...
                      Read this:
                      https://www.circuitspecialists.com/b...ower-supplies/

                      "Not a Speaker Designer - Not even on the Internet"
                      “Pride is your greatest enemy, humility is your greatest friend.”
                      "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                      Comment

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