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Thread: JBL 4311B Restoration Questions?

  1. #1
    Senior Member Baron030's Avatar
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    Feb 2005
    Chicago, Illinois

    JBL 4311B Restoration Questions?

    I have a pair of JBL 4311B speakers that are in pretty good condition.
    But, I need to replace the L-Pads. And while I am at it, I plan on replacing the capacitors as well.
    And the grill cloth has come loose, so I need to re-glue and/or replace the grill cloth.
    Otherwise, they appear to be minty.

    So far, I have removed the woofer and looked inside.
    The crossover appears to be attached to some 1/8 Masonite.
    Now, I have already found the schematic. So, I don’t need help there.

    Does anyone know how is the Masonite attached?
    Are there screws with the screw heads hidden under the foil decal?
    Or is this Masonite glued and I should gently break it free?

    I don’t want the mess with the foil decals unless that is necessary. Any advice would be helpful.


  2. #2
    Senior Member gdmoore28's Avatar
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    Jan 2014
    I don't know the answer to your question, but I'll bet you can test the presence of hidden screws behind the foilcal by using a small magnet pickup tool. Probe across the foilcal, and the magnet should latch onto any blind screws.


  3. #3
    Senior Member jbl4ever's Avatar
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    Dec 2005
    McHenry IL

  4. #4
    Senior Member
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    Jan 2005
    Hi Baron! Did that job on a 4312 - same diff, as I recall. Yes, there are screws under the foilcal. Just use a hair dryer and razor blade scraper. Just get an edge loose and then gently pull/lift it off. I measured the caps and they were in spec so I re-used them. Sounded fine. Mike

  5. #5
    Senior Member Baron030's Avatar
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    Feb 2005
    Chicago, Illinois

    Keeping them in the family

    I thought that I should follow up and thank everyone for their help. Jbl4ever was very helpful in posting the service manual, which clearly shows that removing the foilcal is required. And Mannermusic was spot on with the hair dryer trick. And I also want to thank Steve at Huntley Audio for selling replacement grill cloth that looks identical to the original. And seaman for his “Zilch Cloth Installation” posting without all of your help my project would not have turned out so nice.

    A little background on how I got these 4311s. My brother in law purchased these way back in the late 1970s, when a few audio stores went out of business. And he got a deal on some sales floor models. So they were never a matched pair. Recently, when my sister and brother in law moved to Colorado, I was asked if I wanted these for free. Needless to say, it was an offer I could not refuse.

    Other than some marks and stains on the foilcals from where the “goop” ran down from the woofer. I now have these looking pretty nice. And to get these to sound right, I replaced the caps and l-pads and then adjusted the l-pad setting using my copy of CLIO speaker testing hardware/software. As you can see on the close up picture, the actual l-pad settings are all over the map. But, acoustically the levels are dialed in to give as flat a response curve as I could get. And these are now a matched pair and back to sounding like new again.

    Last night, my great nephew Kyle came by to pick up his belated Christmas present. Kyle is now the proud owner of a pair of JBL 4311b control monitors, which were originally owned by his grandfather. Needless to say, Kyle is thrilled.

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  6. #6
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    Oct 2003

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