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Thread: JBL L112 - Crossover Confusion

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    JBL L112 - Crossover Confusion

    Ok, I did a little searching on this but didn't get all my questions answered. Hopefully I won’t confuse everyone. So, to get this twisted story rolling here is part one:
    I have two L112s that I’ve been sprucing up. First thing I noticed when I took them apart was that they didn’t have the same xovers in them. Since then I bought two used ones which are in great shape and the L-pads are smooth and quiet. I will replace the old ones with them. During my research to buy the new ones I saw three types of xovers for JBL L112s which don’t look exactly the same, one of which is totally different (one of my old ones that I’m replacing). I had one xover that was built on a black plastic backboard (hereinafter referred to as blacky) and had a nice pc board for all the components. The other cabinet had an xover built on a brown pressboard material (hereinafter referred to as brownie) and did not have a printed circuit board but just had components jumbled together on the board. I thought brownie was actually a patch/fix job done by someone before I got the cabinets which is why I originally wanted to replace it to be original. But, after pulling them out I saw that ole brownie was actually a factory board (it also came from a cabinet with a much higher serial number). So that covers 2 of the three. The third I’ve seen is just like the black one here but one of the chokes was much larger (the choke at the bottom of the board). So, here are some pics I took of my two old ones:
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    So with that said, has anyone has seen this in the past? Anyone know the diffeneces if any between these 3 xover configs? More to come...

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    A little more info to add before I call it a night. I did some wire tracing and I suspect (to the degree of around 90% positive that) these speakers have been running with polarity issues. What would be a help is if someone could verify that the black striped wire for LF,MF, and HF are in fact supposed to be on the negative terminals of their respective xover connections. Also, on the LE5-12 midrange, which wire connector is positive, the male or female? And last, on the 044, there is a + molded into the aluminum housing on the back side where the tweeters male terminal is, is the positive wire from the xover to connect to this terminal?
    Sorry for all the rudimentary questions. Problem is I have 4 xovers with three diffenent wiring configs and don't know which one to trust,,, in a nutshell, I've got a clustery situation on my hands.
    I'll also try to search here for some old documentation that may have schematics. Thanks.

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    Thanks Zilch. I found this link too on the JBL site. The tech sheet you linked is what I really needed though. Figured I'd post this incase someone needed it.
    http://manuals.harman.com/JBL/HOM/Ow...ual/L112om.pdf

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    Hi,

    the larger (bass) coil at the bottom would be an air coil with the same 2.5mH value as the smaller iron coil but preferred for lower distortion, also more costly.
    I have seen both types installed in L96/L112/L150A which have the same networks.

    regards taro

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    Senior Member DavidF's Avatar
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    Quote Originally Posted by scubadude View Post
    A little more info to add before I call it a night. I did some wire tracing and I suspect (to the degree of around 90% positive that) these speakers have been running with polarity issues. What would be a help is if someone could verify that the black striped wire for LF,MF, and HF are in fact supposed to be on the negative terminals of their respective xover connections. Also, on the LE5-12 midrange, which wire connector is positive, the male or female? And last, on the 044, there is a + molded into the aluminum housing on the back side where the tweeters male terminal is, is the positive wire from the xover to connect to this terminal?
    Sorry for all the rudimentary questions. Problem is I have 4 xovers with three diffenent wiring configs and don't know which one to trust,,, in a nutshell, I've got a clustery situation on my hands.
    I'll also try to search here for some old documentation that may have schematics. Thanks.
    The "brownie" may be a handwired version of the L112 crossover, after all. You will have to match up the component values.

    Follow the schematic posted by Zilch for answers to the driver hook up. The color-with-black striped wire runs back to the black terminal (aka negative) for each leg of the xover. The driver leads shown in the schematic should be hooked as shown by the arrows. "-----<" means to hook this lead to the male terminal on the driver. "------>" to the female terminal. So, the mid driver is wired opposite phase of the low and high by design.

    DavidF

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    Using the schematic posted by Zilch I was able to get to the bottom of this. The two crossovers I bought were wired correctly as was the old brown one. For some unknown reason all of the black stripe wires were on the positive terminals of my old black crossover. So, the speakers had been running out of phase. I never considered reversing the input wires on the rear of the speaker to see if it sounded better, I assumed the inside was correct,,, never again. To give credit where credit was due, I had to spend some time on the black crossovers to tighten up all of the push on terminals which were all loose IMHO. The brown crossover was all soldered and solid. I have one speaker completely rebuilt (cleaner L-pads and new xover, reconed in 1999 128H, used but mint LE5, and a clean 044) except for replacement of the foilcal. Not sure what adhesive to use for that. Thanks again for the input on this.

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    Zilch, just curious, how did you get to that link on the Harman site? I can navigate to the owners manuals but not the tech sheet you found. Only thing I could do was replace the "l112" with things like "l150" to get different sheet.

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    Quote Originally Posted by scubadude View Post
    So with that said, has anyone has seen this in the past?
    Oh hell yes! I've seen every iteration since they first rolled off the line.
    Quote Originally Posted by scubadude View Post
    Anyone know the diffeneces if any between these 3 xover configs? More to come...
    Yeah, some used older 0.068 uF transcaps, some used newer 0.01 uF transcaps. Some used an IC inductor on the LE10/128 and some used an AC inductor on the LE10/128. Some were hand wired and some were PCB. I personally watched one woman hand wire one in the early days.
    Quote Originally Posted by scubadude View Post
    Zilch, just curious, how did you get to that link on the Harman site?
    I taught him. Technically it's nobody's business but we provide links to it anyway. After all, this is the Lansing Heritage website...

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    LOL, thanks Giskard. Everything is clear now.

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    Quote Originally Posted by scubadude View Post
    LOL, thanks Giskard. Everything is clear now.
    Oh good, that means you are tossing that stuff in the trash and building your own charge coupled versions with new components right?

    Seriously though, just find a matched pair of networks and one should be good to go. It is kind of irritating to start pulling these things apart and running into unmatched pairs. Obviously the PCB version with the large AC inductor is the most desireable stock version.

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    That's what I was thinking. So, it was out with the old and in with the new matched set. They don't have the large inductors but they are a really clean set, the L-pads alone were worth the purchase since the old ones were fairly oxidated.

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    Quote Originally Posted by DavidF View Post
    ...The driver leads shown in the schematic should be hooked as shown by the arrows. "-----<" means to hook this lead to the male terminal on the driver. "------>" to the female terminal. So, the mid driver is wired opposite phase of the low and high by design.
    Uh, no.

    The BLACK striped lead (???/BLK) connects to the Black terminal of the drivers in all cases. You will note this on drivers like the LE5-XX's which have the M/F connectors - the networks are pre-wired this way.

    If I read correctly, your post is exactly opposite of convention (not withstanding the specific MF comment).

    Also, to scubadude, the intended "POS" terminal of vintage JBL drivers is marked with a (+) and/or a red dot (even though these are the (-) post by current industry convention).

    Here we are once again...
    bo

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    Quote Originally Posted by scubadude View Post
    ...For some unknown reason all of the black stripe wires were on the positive terminals of my old black crossover. So, the speakers had been running out of phase.
    No, someone rewired them to reverse the electric "phase" of the drivers' response. Vintage JBL drivers are "negative polarity" - cone in on (+) signal. Your seller apparently went to the trouble of "correcting" that, in the cabinet. JBL sez you can take care of this by connecting the entire cabinet Red to Black on the terminals.

    If, as you say, all the connections were reversed, then the relative driver phasing was being preserved to match JBL design - that is, the MF was opposite the LF and UHF, as is common in 3-way configurations (although the group was overall opposite what JBL designed). You can see this on the L112 tech sheet - the WHT/BLK connector for the MF comes from the RED input lead, driving the MF "reversed" so that (+) signal will give cone out movement for the MF.

    Quote Originally Posted by scubadude View Post
    I never considered reversing the input wires on the rear of the speaker to see if it sounded better, I assumed the inside was correct,,, never again.
    You make a VERY IMPORTANT POINT. Buyers of vintage audio gear - in-particular speakers - should thoroughly check the driver compliment, network wiring and in-cabinet connections to ensure things are as expected. This is not always so.

    There actually is no right or wrong, although this is argued. To honor the music as if someone was performing at the end of your room the LF cones should move out on (+) signal. However, I've run my JBL's "backwards" from industry convention - but true to original JBL design - for decades. You can reverse the cabinet hookups, if you choose. It is really only important that each cabinet in a stereo pair are identical, AND that you do not stack/pair these with non-JBL brands (which will result in cancellations). Most SR and pro-gear documents are full of "warnings" about this, to make sure Main "stacks" and monitor wedge groupings are of consistently polarity.
    bo

    "Indeed, not!!"

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