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  • Mackie Thump TH-12A issue

    My Mackie TH-12A is not working properly since a while. It started to sound intermittently when I put the volume up. When I started to test what's really going on I found out that the problem comes from the bass frequencies. At low volume the speaker sounds perfectly, when you raise the volume it start to pump up intermittently as I said, in that volume if you low down the bass frequencies with the EQ it sounds ok again and, of course, when the music that I'm playing through it lacks of bass frequencies it works perfectly. So you can tell that the bass frequencies switch on and off while the trebles keep always sounding. It's like there's a threshold of pressure in the LF speaker that when you pass it startsto do this weird thing. I hope you can understand this explanation. I checked the circuit and everything looks neat so I have no idea of where to start. Any idea? I can't find the schematics of this model, I could find the TH-15A one which is quite similar so I can show you if that helps to solve the problems. Thank you.

  • #2
    I would bet my money on the filter capacitors, or a faulty woofer.

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    • #3
      Thx. I'm gonna try to plug another woofer and if it's still making the same thing I'll replace the filter capacitors. Btw I didn't get a notification of your answer and I'd swear that I enabled the option.

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      • #4
        The email notifications do not always work. Not sure if it is related to the 'double post' issue or not.
        Originally posted by Enzo
        I have a sign in my shop that says, "Never think up reasons not to check something."


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        • #5
          Look on Ebay. There are some guys that fix those boards flat rate. What was funny though was LOUD tech once told me these Ebay services were a reason for their lack of parts. LOL

          That problem can be related to anything from the SMPS to actual parts in the PWM driver. Some have found bad diodes, others have been related to the actual drive IC's and some were issues with the speaker drivers themselves. LOUD will sell you a new board for $250 though.

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          • #6
            So I tried with another speaker and it was working greatly, so it's the speaker. I'm gonna try to fix it with a method that they told me in case that the coils is displaced. Facing it down on the floor and hitting the magnet with a hammer. Otherwise I'll just replace it. Thanx for your help, guys.

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            • #7
              They told you to hit it with a hammer?
              That's a novel approach!
              Originally posted by Enzo
              I have a sign in my shop that says, "Never think up reasons not to check something."


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              • #8
                Hahaha, yeah, a friend of mine that worked in a repair shop said that he learned it from his boss. It's worth to try cause I otherwise I'd have to rip off the speaker to get into the guts and then recone it back. I just prefer to swap the speaker before having to do all that.

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                • #9
                  Hitting it with a hammer is poor advice. Please don't do that. You could break the magnet, shift the gap, and end up with a paper weight. Not only that, but with the dust cap still attached, any loose particles aren't going to be able to escape anyway.

                  Instead, carefully cut off the dust cap and inspect it. Turn it face down and LIGHTLY bang it on the bench to see if anything falls out. There could be a chunk of glue or other debris stuck between coil and pole piece. Also check to see if glue is loose anywhere (maybe the spider is loose). Check that there are no tears. You can also insert shims between the coil and pole piece to see if something comes loose. I've even reformed elliptical coil forms using shims. You can glue on a new dust cap easy enough after you've inspected and/or repaired it.
                  "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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