JBL PB12-Sub and Amp Question

Discussion in 'Speakers & Subwoofers' started by Matt^Brown, May 25, 2005.

  1. Matt^Brown

    Matt^Brown Supporting Actor

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    I just bought an old JBL PB12 off of ebay for $42. The JBL amp has blown and the guy had put a 40watt KLH amp in its place. Well this sounded like garbage. I currently have a B.I.C. VL1220 and I would not have bought the JBL but for such a low cost I figured it would be a fun toy. My first question is should I put another plate amp in the box or should I just seal the box and use an external amp? Would I be better off trying to have the original JBL amp repaired? Also should I fill the box or just leave it empty? Last question is should I change out the sub?
     
  2. Legairre

    Legairre Supporting Actor

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    Matt,
    If the original owner put a 40 watt amp in a sub with a 12" drive (the original amp was 250w) I'm not surprised it sounds bad. That's a pretty big driver for only 40 watts. If it were me I'd get a plate amp from partsexpress.com. You can always cut the box to make the new amp fit. Here's a link to some plate amps at pretty good prices.

    http://www.partsexpress.com/webpage....ctGroup_ID=505
     
  3. SteveMetcalf

    SteveMetcalf Agent

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    Before repairing or replacing the amp, I'd have the driver checked. Chances are this amp has been clipping like crazy, you may have a bad driver as a result. If the driver is good, replace the 40watt crapper with the original jbl amp. This amp was designed with the characteristics of the speaker in mind and can dampen it's movements properly. You don't know if a plate amp will work as well.
     
  4. John Garcia

    John Garcia Executive Producer

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    Early veresions of the JBL PB-10 and PB-12 were very well known for having amp failures, and the damage usually extended beyond the amp failing due to the nature of the failures so Steve's recommendation is a good one - find out if the driver was damaged because there is a good chance of this. A friend of mine had it happen - he said the sub started a very loud, low warble and the amp actually smoked when whatever it was in the amp finally fried.

    You would probably be able to replace the entire amp for the cost of repairing the one in there.
     
  5. Matt^Brown

    Matt^Brown Supporting Actor

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    Well thanks for the input guys. If the sub is blown is there a sub that you would recommend placing in a box of this size? I am leaning towards just replacing the sub with something else and then buying an amp that will work with the new sub.
     
  6. SteveMetcalf

    SteveMetcalf Agent

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    Your best bet on finding a good sub, is to first contact JBL and obtain the Thiele-Small parameters for the speaker you have now. Enclosure calculations are done with these specs in mind, so by finding another brand with similar characteristics you will have a similar sound when you place a new speaker in the enclosure.
     
  7. chuckg

    chuckg Supporting Actor

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    The amp in my PB12 always had a buzz - likely the transformer or some sloppy parts in the power supply. The amp finally quit, sort of. What happenend was that the magic on/off circuit began turning on and off quite rapidly. I was going to write "rabidly" and maybe that's better.

    Anywho, I disconnected the JBL plate amp and connected a terrible little Radio shack PA amplifier I had laying about. The sub never sounded better! Now I have a real workhorse 200 W amp sitting on top the sub. It kicks!



    If both the amp and the driver are bad, toss the whole thing and start over. You can purchase the driver straight from JBL - go to their home audio support section.
     

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