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Thread: JBL 123A Voice Coil Rub

  1. #1
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    JBL 123A Voice Coil Rub

    I was listening to my L88's hooked up to a Marantz 2330B receiver at a moderate listening level today when one speaker started to cut out. Not knowing if it was the receiver or the speaker I swapped the speakers from right to left and sure enough, it was the speaker. Gently pushing in on the woofer dust cap, I could feel the voice coil rubbing.

    Is there any hope of having it repaired? They are mint condition.

  2. #2
    Senior Member Eaulive's Avatar
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    If it was cutting out, I doubt it's the voice coil rubbing, I would check the connections (cat wiskers) from the cone to the push connectors, a bad connection can create a scratching sound when you move the cone under load (i.e: connected to an amplifier output.)
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    Thanks, I'll pull the woofer out over the weekend and take a look.

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    voice coil is fine, but...

    For some reason, the speakers have been fine for the past few weeks, but yesterday, I hooked them up to a different amplifier and the same speaker started to cut in and out again. I pulled both woofers out to look at the x-overs and it looks as though one of the capacitors is bulging at the top, the cap in the other x-over is flat.

    The x-overs in my speakers consist of only a 8 ohm L-pad and one capacitor that has no value stamped on it.
    Does anyone know what the correct value is?
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    Well, I did a little web browsing and came across this thread...

    http://forums.audioholics.com/forums...xover-cap.html

    looks like the value of the capacitor (part number 10391) is 8 uF, just thought I'd pass it along...

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    Senior Member BMWCCA's Avatar
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    Yeah, what you need is also linked to from this site's library:

    http://www.jbl.com/resources/Brands/...0nova%20ts.pdf
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    The link you posted seems to be for an earlier L88 model. I posted the same schematic in post #4 just for comparison. Compare it to the photo I posted, they are completely different crossovers.

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    Heather [Senorita member] hjames's Avatar
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    That looks like the satellite board that would mount on the baffleboard behind the foilcal.
    That has less parts than the schematic shown as correct.
    Where is the rest of the crossover?
    Have you followed the wiring within the cabinet to confirm that's all there is in there?

    Are you the original owner and can you confirm it has not been "improved" by a previous owner ... (such things happen)

    Perhaps you should add the parts shown in the schemo to make it match the specified design?

    Quote Originally Posted by malden View Post
    For some reason, the speakers have been fine for the past few weeks, but yesterday, I hooked them up to a different amplifier and the same speaker started to cut in and out again. I pulled both woofers out to look at the x-overs and it looks as though one of the capacitors is bulging at the top, the cap in the other x-over is flat.

    The x-overs in my speakers consist of only a 8 ohm L-pad and one capacitor that has no value stamped on it.
    Does anyone know what the correct value is?
    2ch: Oppo, JoLida 502CRC, JBL L212, 18ti,240ti; Heath AS101, Von Schweikert VR4
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    As far as I know, they are original. There are no other components inside the cabinets except for the drivers. I have 2 sets of L88's, a much earlier version and the pair in question. The earlier version has a crossover that matches the attached schematic and is also behind the foilcal.

    There is currently an online auction for 2 pairs of L88 crossovers and they both look identical to the crossover in the photo I attached.

    The thread that I linked also confirms that there was more than one version offered by JBL.

  10. #10
    Heather [Senorita member] hjames's Avatar
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    Quote Originally Posted by malden View Post
    As far as I know, they are original. There are no other components inside the cabinets except for the drivers. I have 2 sets of L88's, a much earlier version and the pair in question. The earlier version has a crossover that matches the attached schematic and is also behind the foilcal.

    There is currently an online auction for 2 pairs of L88 crossovers and they both look identical to the crossover in the photo I attached.

    The thread that I linked also confirms that there was more than one version offered by JBL.
    So - I gather you are not the original owner?
    And you do not know if they have been tweaked before you got them?

    I also gather there is no labeling on the yellow cap shown in your photo?

    From what I have seen, JBL made running changes to improve a product (based on some of the dated charts for the Pro speakers).
    Why not revise the crossover to the same design your other pair has?
    Get the correct caps from a supplier, put them in the circuit and be done with it.
    2ch: Oppo, JoLida 502CRC, JBL L212, 18ti,240ti; Heath AS101, Von Schweikert VR4
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    I think it's obvious that I am not an authority on the L88's or JBL in general. I provided the information I have which may or may not be conclusive.

    If you are trying to make a positive contribution to this thread, please provide some useful information.

  12. #12
    Heather [Senorita member] hjames's Avatar
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    Quote Originally Posted by malden View Post
    I think it's obvious that I am not an authority on the L88's or JBL in general.
    I provided the information I have which may or may not be conclusive.

    If you are trying to make a positive contribution to this thread, please provide some useful information.
    Gently gently ... I am not trying to ding on you - you just said "As far as I know, they are original."
    and I was trying to find out specifically if you were the original owner or if you bought it used.
    Either way, there is no need for anger, lots of us own speakers we did not buy new.

    But the L88 was a lower price model - so if the caps have no writing on them, and it seems like its not a
    well documented variation of the production version, I'm guessing you can go buy an 8 µF metalized polypropylene cap
    from Parts Express (part 027-426) or Madisound like that other thread suggested.
    http://forums.audioholics.com/forums...xover-cap.html
    It seems to me like the best approach would be to make it match the documented version of that speaker.

    That's all I am trying to get at here ... no flames meant.
    2ch: Oppo, JoLida 502CRC, JBL L212, 18ti,240ti; Heath AS101, Von Schweikert VR4
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    I know nothing about electronics but I just realized that the capacitor is probably a "high pass filter" and has no affect on the woofer.

    Can someone please confirm this?

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    Quote Originally Posted by Eaulive View Post
    If it was cutting out, I doubt it's the voice coil rubbing, I would check the connections (cat wiskers) from the cone to the push connectors, a bad connection can create a scratching sound when you move the cone under load (i.e: connected to an amplifier output.)
    I came across a website the other day where someone reconed a 123A-1 because the voice coil was rubbing only to find that the foam filter inside the magnet assembly had deteriorated and some had got lodged in the voice coil gap. Can't find the link but will post when I do.

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    Found it!...

    http://ka7oei.blogspot.com/2013/01/dang-it-jbl.html

    not sure if this pertains my driver...

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