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Thread: Polarity questions, L100 Century

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    Junior Member Theonetruegreg's Avatar
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    Polarity questions, L100 Century

    Using the original, vertical L100. These have been taken apart before by previous owner. I have owned them for a few years now, and they have been fine and good, but have some questions about how they are wired and if it is correct (especially trying to present the proper 8ohm load to an amp)

    When testing the LE5-2 midrange, it seems that the black/red are reversed at the terminal. Applying voltage to them resulted in the black seemingly being the positive terminal (pushing the cone outward)

    I can't look at the back of the tweeter the way it's mounted, but the woofer is wired as the schematic shows (black to black, green to red)

    The midrange is currently wired black to black, white to red.
    The question is, is this wiring of the LE5-2 correct? (as the schematic does not show which terminal it should go to) Seeing as how the black terminal is actually the positive input.
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    Junior Member Theonetruegreg's Avatar
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    Someone out there has to know this. I have seen the little chart in another thread, but that lists + being inward movement on the drivers used, which is untrue of the 123a in there, so I don't fully trust it

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    Senior Member DavidF's Avatar
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    Quote Originally Posted by Theonetruegreg View Post
    Someone out there has to know this. I have seen the little chart in another thread, but that lists + being inward movement on the drivers used, which is untrue of the 123a in there, so I don't fully trust it
    Keep mind some general (meaning you may find exceptions) JBL conventions in this time period.

    A wire with a color or white goes from the xover to the input terminal of driver.

    A wire with black or black striping goes to the return terminal of the driver.

    I use the terms "input" and "return" as to the terminals and avoid using positive or negative to try to minimize confusion.

    Drivers will produce an inward movement when a positive signal is applied to the driver input terminal.

    Donít really know why JBL used this polarity convention (up until the last couple of decades anyway) but that is what you are dealing with here.

    In terms of the schematic you posted, the woofer return terminal (black) is actually fed through the system input terminal (red). So you have in effect a reversal in polarity causing woofer cone to move outward with positive signal to system input.

    The mid and tweeter are wired such that the system input terminal connects to the driver input terminal. Therefore, cones move inward with positive signal to system input.
    David F
    San Jose

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    Junior Member Theonetruegreg's Avatar
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    Quote Originally Posted by DavidF View Post
    Keep mind some general (meaning you may find exceptions) JBL conventions in this time period.

    A wire with a color or white goes from the xover to the input terminal of driver.

    A wire with black or black striping goes to the return terminal of the driver.

    I use the terms "input" and "return" as to the terminals and avoid using positive or negative to try to minimize confusion.

    Drivers will produce an inward movement when a positive signal is applied to the driver input terminal.

    Donít really know why JBL used this polarity convention (up until the last couple of decades anyway) but that is what you are dealing with here.

    In terms of the schematic you posted, the woofer return terminal (black) is actually fed through the system input terminal (red). So you have in effect a reversal in polarity causing woofer cone to move outward with positive signal to system input.

    The mid and tweeter are wired such that the system input terminal connects to the driver input terminal. Therefore, cones move inward with positive signal to system input.
    Thank you sir, that was quite helpful

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