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Thread: JBL 4311 passive bi-amp question

  1. #1
    Mike Kay
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    Question JBL 4311 passive bi-amp question

    Hello Folks,

    I would like to bi-amp my lovely set of JBL 4311's but retain the passive crossovers. That is power the woofers off each side of a stereo power amp, and power the mids and highs off of a different stereo power amp. Maybe tubes upstairs, and solid state raw power downstairs you know?

    And I would like to retain the exsisting 4311's crossover at the same time. Has anyone out there accomplished this mod? I would love to learn how and utilize the benifit of this fine forum.

    Thanks!
    mikekonopka.com

  2. #2
    Administrator Robh3606's Avatar
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    Well you could passively biamp them quiet easilly. The woofer runs wide open. So add an set of extra posts, run the woofer wires to them keep the mids and tweeter on the originals and you are done as far as speaker mods are concerned. Just hook up your amps and go. Try it. You will get the most benefit with a active crossover as far as biamping goes but active may do more harm than good. Messing with the crossovers will change their characteristic sound.

    Rob

  3. #3
    Mike Kay
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    Thanks Rob,

    Wow! This is far easier than I had envisioned. I concurr that while burning a few watts of power, the passive crossover is the best bet to retain the classic sound and benefits from JBL's R&D on crossover design. An active circuit would be more efficent but not as sweet sounding.

    While I'm adding an extra set of posts on each 4311, I think I will change out the stock posts to banana stlye to accomodate larger gauge wire than the old push style posts currently in place.

    Thanks again,
    MK

  4. #4
    Senior Señor boputnam's Avatar
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    Hey, MK...

    If you're interested, here's the 3111 schematic, showing what Rob described - the "woofer runs wide open". It is allowed to roll-off naturally on the top end (bottom end, too... ).
    Attached Images Attached Images
    bo

    "Indeed, not!!"

  5. #5
    Bruno GINARD
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    Mike,

    I have made this modification 15 yars ago on a modified 4311. (Box was made of 2 parts, one for LF/MF, another for LF).

    You must disociate the LF and MH/HF circuits on the filter ( they have a common earth, you need 2 separate earth).

    You can take advantage of the mod. in changing the caps for best quality models. The filter scheme is so basic ( and IMO that's why the 4311 are great !) that it could be replaced with "top" components .

    I have used Paper oiled caps.(1 Kv !)

    For the amplifiers, the best solution was made with 2 equal amps (at this time, 2 Electrocompaniet ) . Using differents amps gave less definition and balance, IMO because there are a lot of differences in parameter ( Slew rate, damping factor, sensitivity, input impedance....)
    The worst solution was a valve amplifier ( 6550 PP in a Williamson configuration) for the low, and the Electro. 25 W Class A for the Highs.
    I have noticed the same consequences in Bi_amping passively "my 15" Tannoy coaxial.

    Compared with an active filter, i think it will be a pity to lose the simplicity of the original scheme .....

    Good luck

  6. #6
    Mike Kay
    Guest
    Thanks for all the help guys!

    Can anybody give me more info on those paper oiled caps that Bruno speaks of? Like where to find them and costs, etc. That would be great!

    Mike Kay

  7. #7
    Bruno GINARD
    Guest

    ABOUT CAPS

    Paper with oil, or polypropylene and paper with oil capacitors are used in High voltages circuits, discharge circuits and everywhere you need a reliable component.
    For example, circuits in the French high speed Train use this kind of caps.

    For the HIFI use, they are perfect for high voltages in valves amplifier supply, especially 211 and 845, scheme.
    For speaker filter, I prefer them instead all SOLEN, SCR, Black Gate and others, because they are very neutral, have no mechanical vibrations, and have a very long life. Mr KOIZUMI, of ONKEN, uses only Pap. Oiled caps in there speakers.

    There are only two problems: Price, and dimension!
    Enclosed I put a pic of my old filter for the 15” Tannoy. You will understand the “dimension” problem

    My caps were made by Eurofarad, a French company (supplier of caps for all the industry).
    See the link, and search Products -) capacitors -) power electronics -) PLP /PAM
    WWW.EUROFARAD.COM


    I am sure you can find the equivalent in USA, but I don’t know the supplier…. Maybe Mallory make them…. Try on the Web by a search engine


    Regards
    Attached Images Attached Images  

  8. #8
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    So has anybody successfully done this?


    Quote Originally Posted by Mike Kay View Post
    Hello Folks,

    I would like to bi-amp my lovely set of JBL 4311's but retain the passive crossovers. That is power the woofers off each side of a stereo power amp, and power the mids and highs off of a different stereo power amp. Maybe tubes upstairs, and solid state raw power downstairs you know?

    And I would like to retain the exsisting 4311's crossover at the same time. Has anyone out there accomplished this mod? I would love to learn how and utilize the benifit of this fine forum.

    Thanks!
    mikekonopka.com

  9. #9
    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by JBL Nicholas View Post
    So has anybody successfully done this?
    If you're referring to the crossover mods, I suppose Bruno actually did, but he hasn't been here for nearly two-years.
    To me it looks like a lot of pain and expense for what must be very little (if any) gain.

    If you're talking about simply a passive bi-amp, can't imagine it would actually do much, either, but then it's so simple to try even without adding binding posts. Just disconnect the woofer at the Fast-on connectors and run the bass amp to it directly. I doubt even active bi-amping would be much of an improvement simply because these are relatively efficient on their own and just don't need that much power to do what they do, which is to not produce much deep bass, anyway.
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

  10. #10
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    Quote Originally Posted by BMWCCA View Post
    If you're referring to the crossover mods, I suppose Bruno actually did, but he hasn't been here for nearly two-years.
    To me it looks like a lot of pain and expense for what must be very little (if any) gain.

    If you're talking about simply a passive bi-amp, can't imagine it would actually do much, either, but then it's so simple to try even without adding binding posts. Just disconnect the woofer at the Fast-on connectors and run the bass amp to it directly. I doubt even active bi-amping would be much of an improvement simply because these are relatively efficient on their own and just don't need that much power to do what they do, which is to not produce much deep bass, anyway.
    No one cares what you think about L100s

    Everyone within earshot has heard it now, your pretentious disdain for them, OVER AND OVER AND OVER already

    Why you feel compelled to get your little dig in on them EVERY TIME they come up I have no idea

    A concision maybe you can understand:
    NO ONE THAT LIKES L100s GIVES A CRAP WHAT YOU OR ANYONE ELSE THINKS ABOUT THEM

    Thomas

  11. #11
    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by Wagner View Post
    No one cares what you think about L100s

    Everyone within earshot has heard it now, your pretentious disdain for them, OVER AND OVER AND OVER already

    Why you feel compelled to get your little dig in on them EVERY TIME they come up I have no idea

    A concision maybe you can understand:
    NO ONE THAT LIKES L100s GIVES A CRAP WHAT YOU OR ANYONE ELSE THINKS ABOUT THEM
    I didn't notice anyone saying or asking anything about your beloved L100.
    Did I say anything that wasn't true?
    Climb back in your hole and leave us the hell alone!
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

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