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Thread: Am I building these correctly - JBL 4355 Crossovers

  1. #16
    Senior Member martin2395's Avatar
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    Thanks for the advice macaroonie!

    Odd, the schematics you posted has more components, why is that? L4 and R16 for the mid and for L5/R6 HF.
    They aren't noted on the layout posted in 2010 and on Giskard's 3155.

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    I now also know that the drawing i posted before is wrong - the caps are all in series where some should be (2x paralell) + (2x paralell) in series.

  2. #17
    Senior Member Odd's Avatar
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    They will flatten the impedance.
    Giskard have explained this in a post, can not find it now.
    43XX (2235-2123-2450-2405-CC 3155)5235-4412-4406-4401-L250-18Ti-L40-S109 Aquarius lV-C38 (030) 305P MkII

  3. #18
    Senior Member macaroonie's Avatar
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    Martin you should check whether the inductors should be wound to as low a DCR as possible or whether there should be an R value specified.
    Some networks use the DCR as a component of the network and the wind intentionally is (6ohm) kept at a value that does influence the filter.

    The guy at the link I sent you can do it whatever way you need , is very helpful also.
    Tell him I sent you.

    Mac

  4. #19
    Senior Member martin2395's Avatar
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    AFAIK the DCR value of the original 3155 coils is unknown and in another thread here on LH someone said to use coils that have DCR not higher than 1/20th of the driver's impedance.

    From the specsheet of the original 3155: http://puu.sh/catfk/1b4790e8d9.png

  5. #20
    Senior Member Odd's Avatar
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    Quote Originally Posted by martin2395 View Post
    AFAIK the DCR value of the original 3155 coils is unknown and in another thread here on LH someone said to use coils that have DCR not higher than 1/20th of the driver's impedance.

    From the specsheet of the original 3155: http://puu.sh/catfk/1b4790e8d9.png


    I do not know, but I think "4313B" have the answer.
    43XX (2235-2123-2450-2405-CC 3155)5235-4412-4406-4401-L250-18Ti-L40-S109 Aquarius lV-C38 (030) 305P MkII

  6. #21
    Senior Member martin2395's Avatar
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    I've sent him a PM.

  7. #22
    Senior Member martin2395's Avatar
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    Ok, i asked some other people and been told to keep the DCR as low as possible. The drawing I posted before is wrong, I've reworked it on paper and what do you think, any errors?

    The pics aren't resized so I post them as links:

    MF (fixed an error on the go ): http://nl.tinypic.com/r/2yk04mc/8
    HF http://nl.tinypic.com/r/dy4mxh/8
    UHF http://nl.tinypic.com/r/i4nzpw/8

  8. #23
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    Quote Originally Posted by martin2395 View Post
    Ok, i asked some other people and been told to keep the DCR as low as possible.
    G.T. usually designed around 0.5 ohms for DCR so figure around 0.4 to 0.6.

    If you go higher or lower you will affect the slopes to some degree.

    Just don't use ultra-low DCR coils like some of the Erse designs. They're great for use on the LF transducers or when designed into the network from the start but they should probably be avoided in legacy JBL bandpass filter designs. JBL did use some coils with 7 to 8 ohm DCR in some systems. The 4355 wasn't one of them.
    Quote Originally Posted by Odd View Post
    This is easier to understand.
    Yes, I like that. Looking at my originally posted schematic, it made sense, to me (and within the context of LEAP), at the time.

  9. #24
    Senior Member martin2395's Avatar
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    This makes it a bit tricky then, the 14AWG 2.4mH coil for the 2123H/2202H has around 0.36rdc.
    The 1.0mH Jantzen 16AWG CrossCoil has about 0.34 and the cheaper 16AWG standard wire coils have even lower rdc.

  10. #25
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    Well, I guess I wouldn't sweat it too much because you can always go back and add in little resistors in series with the inductors if it is really necessary.
    G.T. himself has added in a mere 0.2 ohms in some instances simply to get a certain circuit "spot-on".
    I do know that I used 16 AWG and 18 AWG inductors rather than 14 AWG to get the "correct" DCR values in some networks.
    I have a veritable ton of these parts in boxes, I should dig them out someday and see what AWG values they are.

    And .36 DCR is really .4 DCR if you round up

  11. #26
    Senior Member martin2395's Avatar
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    I have a strange feeling, like I just learned something

    What do you think about my drawings, are they correct? Never done it before but some day you have to start

  12. #27
    Senior Member macaroonie's Avatar
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    JBL did use some coils with 7 to 8 ohm DCR in some systems. The 4355 wasn't one of them.

    Ah , Clarity. Thanks 4313b , that's what I was getting at.

    carry on ....

  13. #28
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    Quote Originally Posted by macaroonie View Post
    JBL did use some coils with 7 to 8 ohm DCR in some systems. The 4355 wasn't one of them.

    Ah , Clarity. Thanks 4313b , that's what I was getting at.

    carry on ....
    It is a very good point!

    I noticed with the beginning of the K2 type systems, dating back to the 90's, that G.T. used an obviously complimentary combination of coil DCR and series resistors to get the various notch and conjugate filters just the way he wanted them. When modeling the various networks in LEAP it became obvious that the coil DCR values really did matter in those particular circuits. Using "ideal" coils with no DCR resulted in some pretty messed up simulations.

    Prior to that it was generally "0.4 to 0.6 ohms" in most of the legacy systems. That was before the days of all the notch filters.

    In general though, especially with series coils on low frequency transducers, the lower the DCR the better.

    Case in point - the dual 10 mH coils (~ 1.2 mH DCR) in the Everest II can be replaced with a very nice Erse 20 mH coil having significantly lower DCR in order to help mitigate the "gain" created by the larger DCR. This will reduce output slightly around 60-80 Hz and increase overall balance.

    If one doesn't think that any of this matters one can reference the difference between the L250 and 250Ti. The low frequency performance of the 250Ti was markedly better. Same box, same tuning, same LF transducer. The only think that changed was the low pass circuit on the LF transducer. It turns out that the L250 versus 250Ti was a wonderful case study.

    Another example that M.G. and I discussed way back in the late 70's with respect to the 124A - because that transducer had such a low Q it was discovered that a little more DCR in the low pass coil could actually improve performance in a passive system. Of course the best solution was to simply forget a passive circuit altogether and drive that transducer direct coupled to an amp using an active filter. It did require a completely different enclosure volume/tuning to make it all come together in that case though.

  14. #29
    Senior Member macaroonie's Avatar
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    Quote Originally Posted by 4313B View Post
    It is a very good point!

    I noticed with the beginning of the K2 type systems, dating back to the 90's, that G.T. used an obviously complimentary combination of coil DCR and series resistors to get the various notch and conjugate filters just the way he wanted them. When modeling the various networks in LEAP it became obvious that the coil DCR values really did matter in those particular circuits. Using "ideal" coils with no DCR resulted in some pretty messed up simulations.

    Prior to that it was generally "0.4 to 0.6 ohms" in most of the legacy systems. That was before the days of all the notch filters.
    Thanks. It is probably worth noting that some circuit diagrams will show the coil DCR as what looks like a separate item ( resistor ) This will confuse if the nature of the diagram is not noted.
    Poss snafu situation.

  15. #30
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    Quote Originally Posted by macaroonie View Post
    Thanks. It is probably worth noting that some circuit diagrams will show the coil DCR as what looks like a separate item ( resistor ) This will confuse if the nature of the diagram is not noted.
    Poss snafu situation.
    And JBL is really good at leaving that information out of the schematics.

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