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Thread: L-pad delete how to...HELP!

  1. #1
    Member qcautosports's Avatar
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    Question L-pad delete how to...HELP!

    What's up people. I hope everyone is safe and healthy.
    I recently acquired a pair of L88 Nova speakers. Physical shape is awesome. Issues:
    1. Lpads are wonky. Tried opening and cleaning. Some areas lose sound.
    2. One tweeter (LE25-1) only read 0.6 ohms. I guess its fried although gives out small amount of sound. Should I get a new replacement or a good used one? Any difference between the LE25 and the LE25-1?
    3. How do I bypass the lpads?
    It's been years since my last post and visit so, hello again to everyone. 🤗
    ---::: Pioneer PL71/Empire 999 ev/x/ GE RPX Mono/ Scott Type 299C/ Pioneer CS88A :::---

  2. #2
    Member qcautosports's Avatar
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    Quote Originally Posted by qcautosports View Post
    What's up people. I hope everyone is safe and healthy.
    I recently acquired a pair of L88 Nova speakers. Physical shape is awesome. Issues:
    1. Lpads are wonky. Tried opening and cleaning. Some areas lose sound.
    2. One tweeter (LE25-1) only read 0.6 ohms. I guess its fried although gives out small amount of sound. Should I get a new replacement or a good used one? Any difference between the LE25 and the LE25-1?
    3. How do I bypass the lpads?
    It's been years since my last post and visit so, hello again to everyone. 🤗
    Bump😃
    ---::: Pioneer PL71/Empire 999 ev/x/ GE RPX Mono/ Scott Type 299C/ Pioneer CS88A :::---

  3. #3
    Senior Member grumpy's Avatar
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    An L-pad is (normally) a three terminal device that is functionally the same as the picture below where one terminal is the "+", one is the R1-R2 junction, and the other is the "-" ... the difference being the circuit below has R1 and R2 fixed, where an L-pad allows for them both to be adjusted while it's knob is rotated. If you want to replace an L-pad with fixed resistors and have a good L-pad that's set where you like, just measure the resistance between terminals. Of the three possibilities, you'll get R1, R2, or R1+R2... double check this with a calculator like the one below to see that it makes sense.

    For an 8 ohm L-pad: At one extreme R1 should get close to 8 ohms and R2 very small. At the other, R1 should be minimal and R2 perhaps tens to hundreds of ohms.

    sourced from https://www.erseaudio.com/L-Pad-Attenuation ... one of many such online audio L-pad calculators.

    Name:  Screen Shot 2020-06-05 at 11.33.05 AM.jpg
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    See also:

    http://www.bcae1.com/lpad.htm

  4. #4
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    If you were previously running the L-pads "wide open" you only need to solder the input lead to the output lead and disconnect the ground. When an L-pad is run wide open, the input lead "touches" the output lead and the secondary windings are by-passed.

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    Quote Originally Posted by grumpy View Post
    An L-pad is (normally) a three terminal device that is functionally the same as the picture below where one terminal is the "+", one is the R1-R2 junction, and the other is the "-" ... the difference being the circuit below has R1 and R2 fixed, where an L-pad allows for them both to be adjusted while it's knob is rotated. If you want to replace an L-pad with fixed resistors and have a good L-pad that's set where you like, just measure the resistance between terminals. Of the three possibilities, you'll get R1, R2, or R1+R2... double check this with a calculator like the one below to see that it makes sense.

    For an 8 ohm L-pad: At one extreme R1 should get close to 8 ohms and R2 very small. At the other, R1 should be minimal and R2 perhaps tens to hundreds of ohms.

    sourced from https://www.erseaudio.com/L-Pad-Attenuation ... one of many such online audio L-pad calculators.

    Name:  Screen Shot 2020-06-05 at 11.33.05 AM.jpg
Views: 101
Size:  72.5 KB

    See also:

    http://www.bcae1.com/lpad.htm

    Also, keep in mind, the reason an l-pad is used is to keep a constant impedance across the output of the passive crossover the same throughout any adjustments so that the crossover frequency isn't affected.
    This may help to understand it's function better other than just reducing the output of whatever type of transducer is on that leg.

  6. #6
    Senior Member grumpy's Avatar
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    Yep... has to serve both functions.
    That said, once a satisfactory setting is found, they just become a maintenance issue.

  7. #7
    Member qcautosports's Avatar
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    Thanks for the great information. Ill stay with Lpads. Question now is where t o get a couple of new ones. Im replacing both pots.
    ---::: Pioneer PL71/Empire 999 ev/x/ GE RPX Mono/ Scott Type 299C/ Pioneer CS88A :::---

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    Senior Member SEAWOLF97's Avatar
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    Quote Originally Posted by qcautosports View Post
    Thanks for the great information. Ill stay with Lpads. Question now is where t o get a couple of new ones. Im replacing both pots.
    Before getting too radical, in my experience ......

    have been in your spot many times ... IMHO, L-pads if left in one position too long develop a stickson like bond with the wiper which turns into a dead spot.

    My solution has always been to turn the control knob from one full stop to the other about 10 times (amp off) . Seems to break the bond and clean it up. When done, leave it in a slightly different spot.

    This is NOT a problem unique to JBL ... it comes up in many different brands and my "fix" is universal to them. Works on many other type knobs too.

    Costs you nothing to try.
    Learn to forget

  9. #9
    Administrator Robh3606's Avatar
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    My solution has always been to turn the control knob from one full stop to the other about 10 times (amp off) . Seems to break the bond and clean it up. When done, leave it in a slightly different spot.
    Yes seems to work really well. Have had that issue with electronics as well appears an issue with any wiper device. Lucky there can be an easy fix.

    Rob
    "I could be arguing in my spare time"

  10. #10
    Member qcautosports's Avatar
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    Quote Originally Posted by SEAWOLF97 View Post
    Before getting too radical, in my experience ......

    have been in your spot many times ... IMHO, L-pads if left in one position too long develop a stickson like bond with the wiper which turns into a dead spot.

    My solution has always been to turn the control knob from one full stop to the other about 10 times (amp off) . Seems to break the bond and clean it up. When done, leave it in a slightly different spot.

    This is NOT a problem unique to JBL ... it comes up in many different brands and my "fix" is universal to them. Works on many other type knobs too.

    Costs you nothing to try.
    Done that already. Even went as far as opening the pot. No dice. 😒
    ---::: Pioneer PL71/Empire 999 ev/x/ GE RPX Mono/ Scott Type 299C/ Pioneer CS88A :::---

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