Repair ideas for old JBL Sub-12? - AVS Forum
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Old 07-07-2014, 07:34 AM - Thread Starter
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Repair ideas for old JBL Sub-12?

I've got an old JBL Sub-12 taking up storage space with a bad amp (it suffered the classic Harman amp meltdown). I know its low end, but it served its purpose at the time. I'd hate to just trash the thing and was wondering about what options there were to do some repair and repurpose it. Problem is I don't have the tools and experience to do any cabinet mods and there are no third party amps that fit the cut-out of those harman amps that I know of (if you know of one, please share). I can do a bit of soldering so the question is, is there a way to leave the current amp in the box and still be able to wire it to use with an external amp? Does anyone have any suggestions on other things I can do to get some use for it? Since the subs not worth much, I want to spend the least possible on the project.

Service manual is here if it helps any.
http://www.jbl.com/resources/Brands/...Sub12%20sm.pdf

Last edited by bargugl; 07-07-2014 at 07:40 AM.
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Old 07-07-2014, 08:08 AM
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It would be quite easy to just drill holes through the back wood and insert binding posts, or a speakon, and attach them to an external amp. You can measure the inside volume, the port length and diamater, and then model it in winisd and find a driver that works, however if you're going to do all that work it's probably easier and better to just do a full DIY sub and build the cabinet from scratch. Unless you really like the box or something. I think it would be relatively easy to find a driver that works, there are a lot of 12" available. If you give me the box volume and port length and diameter I can model it and see if I can find any drivers that fit it. You could just use a inuke 1000 or inuke 3000 for power, as they are cheap and good.

You are in the US?
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Old 07-07-2014, 08:17 AM - Thread Starter
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I am in the US. What you describe is a probably a bit more than what I had in mind. Just looking for a simple repair job to try to get some use out of it. I think that the drill holes and insert binding posts should be easy enough to pull off. Thanks for the offer.
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Old 07-07-2014, 09:13 AM
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oh I didn't see that your driver is working. You could just get an inuke 1000dsp and binding posts and use the current driver if it works. Don't drive it super crazy as the inuke 1000 is a bit more powerful than the plate amp. You can use the dsp to put the high pass filter on it, if you can figure out the volume of the box and the port length and diameter to find out what it is tuned to.
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Old 07-07-2014, 09:22 AM
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My JBL Sub10's amp had the same problem about 4-5 years ago. I pulled it open and saw two non polarized electrolytic caps had failed, labeled NP or BP I think they were 10uF. I had some spare 10uF NPE caps with my crossover parts so I swapped them out, the amp has been working fine ever since.

I'd pull the amp and look for any capacitors that look like they are bulging, if nothing else looks wrong with the board I'd be willing to saw replacing those caps will get things working again.
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Old 07-07-2014, 10:57 AM - Thread Starter
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Thanks for the tip. I'll pop it open and take a look at it. I had done so before when it happened a couple years ago and if I remember right, the board looked a bit charred so it may be more than the caps. However, I never looked that closely as it was a convenient excuse to buy a new subwoofer at the time.
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Old 07-07-2014, 06:20 PM
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If there is no obvious cap problem, the easy way out is to wire up an external amp as previously suggested. This might be more than you want to spend but you can always use it to power up another sub later. https://www.parts-express.com/dayton...ifier--300-803

The amp won't care that it isn't installed in the subwoofer enclosure.
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