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  1. #1
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    4343 crossover modifications

    Hi,

    I am using a pair of JBL 4343's. Recently I have replaced some of the caps in crossover used for the 2420 driver and the 2405 slot tweeter with Jensen oil in paper caps. The results were very encouraging, and now I would like to make further improvements.

    In the crossover there is a 52 uF capacitor that the entire signal for the MF, HF and UHF drivers apparently has to pass. Is there any way of getting rid of this capacitor or any other ways of simplifying/improving this crossover?

    I can't biamp, and I am not quite ready for a 1st order filter like the one made by 4343mod (At least not without having seen some measurements).

    I am not an expert in crossovers and any help will be greatly appreciated.

    Crossover schematic

  2. #2
    Senior Member GordonW's Avatar
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    Well, I'd be inclined to make up a "composite" from film caps, to achieve this value.

    A good starter point, would be the 40uf 250V Dayton metallized poly from Parts Express, part# 027-442. Parallel that with the 10uf GE Series 41L 600V poly cap from Madisound (part# GE1041L600), and the 2 uf GE Series 42L 850V poly cap, also from Madisound (part# GE242L850). Personally, this is optional... but I would also aquire a small value (like .016uf) high-voltage polystyrene capacitor, from somewhere like Digikey or wherever, to parallel with this "composite".

    This will give you 52uf, but in a way that minimizes the "artifacts" of having a big cap in the circuit. As you go smaller values in the composite, you go to higher-and-higher grade caps, which improves transient leading edge (ie, very high frequency signal) accuracy, and minimizes inadvertant energy storage issues (ie, smearing).

    The good thing about this, is that all these caps are not more than a few bucks each. For less than $30, you could order the whole bunch, which means that if you hated it, you'd not be out of a significant amount of $$. I'd really doubt you'd hate it, given how neutral I've found these sorts of combinations to be, IIRW.

    Now, another alternative would be, instead of the GE polys, just use the Dayton poly as the "core", and use some of your oil-filled caps as the "booster" caps to achieve the final value. Or maybe even this- the Dayton 40uf, the GE 10uf, a 2uf oil-filled, and the polystyrene... or whatever other combinations of values to achieve 52uf, using whatever oil-filled cap valuse you have on hand. That'd probably be the "best of all worlds"...

    Of course, you could do this with more exotic caps like Hovlands and the like, but IMHO, the cap combo I specified above, will be a LOT better than stock, and going from this to exotic caps will be a very MINOR change, if anything perceptable at all in most cases, from the Dayton/GE/polystyrene combo. It's a matter of hitting the balance of expense vs. performance, and also staying with "stable" stuff that doesn't purposefully do 'tweaky" things to the sound balance, like some extremely high-end stuff tends to do sometimes...

    Regards,
    Gordon.
    Last edited by GordonW; 12-22-2003 at 08:38 AM.

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    Re: 4343 crossover modifications

    Originally posted by jeph
    In the crossover there is a 52 uF capacitor that the entire signal for the MF, HF and UHF drivers apparently has to pass. Is there any way of getting rid of this capacitor or any other ways of simplifying/improving this crossover?
    The 52 uF capacitor needs to stay. Temporarily move the white lead going to the #11 lug on the bi-amp switch to the #10 lug on the bi-amp switch. The input of the 52 uF capacitor goes to the #10 lug. Listen to the system and post your impression here.



    Always double check your connections when modifying circuits. You don't want to accidentally blow up drivers or amplifiers.

  4. #4
    Senior Member Guido's Avatar
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    Quote Originally Posted by Giskard
    The 52 uF capacitor needs to stay.
    This I don't understand.
    The 52 (+4) uF Cap is part of the high pass section of the bandpass for the 2121. Why the HF and UHF can't bypass it?

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    Quote Originally Posted by Guido
    This I don't understand.
    The 52 (+4) uF Cap is part of the high pass section of the bandpass for the 2121. Why the HF and UHF can't bypass it?
    Ok. Let me examine it again.

    ***

    The 3143 schematic posted on the JBL website appears to be wrong. Compare with 3141. Thanks for catching that Guido!

  6. #6
    Senior Member Guido's Avatar
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    Quote Originally Posted by Giskard
    Ok. Let me examine it again.

    ***

    The schematic posted on the JBL website appears to be wrong.
    The schematic on JBLPROSERVICE says HF and UHF BEHIND 52 uF in passive mode.

    I modified my 3143 networks last year, checked this and it is cabled according to schematic.

    Damned, now you confused me

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    I confused you?

    They confused us!

    I really should have paid more attention.

    Just use the 3141 passive schematic. Hang on, let me go look at them both again real close.

    BTW, run your voltage drive with both 8 ohm and 16 ohm loads and compare the results.

  8. #8
    Senior Member B&KMan's Avatar
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    Quote Originally Posted by Giskard
    Ok. Let me examine it again.

    Giskard, If you need or wannt any complementary test of info let me know...

    thanks for all.

    I record test for mesure electrical volta with-out 2231 componend connected into a network if this information is pertinant I put on forum

    Jean.


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    Re: 4343 crossover modifications

    Better yet, do what Gordon stated and be done with it

    That will save me the time and trouble of stepping you through the whole process of taking the HF and UHF out from behind the 52 uF capacitor and then re-adjusting the whole filter

  10. #10
    Tom Loizeaux
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    I would be so easy to bi-amp your 4343s. A second amp, an active crossover and another pair of cables and the flick of a switch, and you've gotten those big, mushy caps out of the signal path, cleaned up all of your drivers and increased headroom!
    I think once you've tried it - you won't go back.

    Tom

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    Unfortunately I can't bi-amp. I am using a homemade tube amplifier that I am really pleased with. I guess I will start out by trying Gordonís suggestion.

    Thanks for your help.

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    Caps

    Hi Jeph

    I too recommend that you do something as Gordon advised, in making up a combination cap from multiples, to arrive at the 52uf value.

    If you are in for some additional experimentation at modest expense, try contacting the eBay seller of 100uf (for $10.00) . Ask him to cross-reference what he has available to the pdf catalog numbers that I've uploaded for you. He may have something in the 40uf range for you. These ("Commonwealth Sprague" MPP in oil) caps are either "identical to" or very similar to some Mallory 370VAC motor-run types that I bought last fall. They are a Metallized Polypropylene "swimming" in oil. My Mallorys' have a very deep and generous lower mid to midrange quality. They also slightly suppress (or compress) transients from the "upper presence" area. One can "restore" these upper areas by adding ( Cascading, ByPassing, Combining, Grafting onto ) other "dry" MPP cap-types. Depending on the ratios chosen you can make some very musical combinations as per Gordons suggestions.

    Here is an eBay seller that I have bought from. His handle is "LiteKeys" . I purchased his CDET ( Cornell-Dublier ) "Film & Foil Bypass Caps". These are old-style, & "huge" for their capacitance, Mylar Film & Foil type. Though they don't have as low a noise floor as "Film & Foil" Polypropylene, they do have a deeper soundstage than most other modestly priced, small, tight, MPP "Metallized-Polypropylenes" types ( especially Solen ) . They are really,a cheap bit of education.

    Just a thought .

    regards <. Earl K
    Attached Files Attached Files
    Last edited by Earl K; 01-10-2004 at 03:19 PM.

  13. #13
    Senior Member B&KMan's Avatar
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    Quote Originally Posted by jeph
    Hi,

    I am using a pair of JBL 4343's. Recently I have replaced some of the caps in crossover used for the 2420 driver and the 2405 slot tweeter with Jensen oil in paper caps. The results were very encouraging, and now I would like to make further improvements.

    In the crossover there is a 52 uF capacitor that the entire signal for the MF, HF and UHF drivers apparently has to pass. Is there any way of getting rid of this capacitor or any other ways of simplifying/improving this crossover?

    I can't biamp, and I am not quite ready for a 1st order filter like the one made by 4343mod (At least not without having seen some measurements).

    I am not an expert in crossovers and any help will be greatly appreciated.

    Crossover schematic

    Hello jeph,

    I'm run a new project = rebuilt my 4343 internal crossover...

    So any hint tips or schematic modification or correction of the original PDF schematic Have strongly appreciate...

    What your final selection of caps, inductor, etc. ???


    thanks for all

    Jean.

  14. #14
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    I have been working on the crossover for quite some time.



    Originally I replaced most of the caps in the crossover used on the HF and UHF drivers with vintage Jensen paper in oil caps (1 uF, 1.5 uF, 1.5 uF and 4 uF). The improvement was big - the highs became a lot cleaner, more listenable and natural sounding.



    Afterwards and replaced the original cabling in the cabinet with Belden cat5 and removed the switching system that allowed switching between the internal and an external crossover. This switching system uses quite few feet of cable inside the loudspeaker cabinet and must be bad for the sound quality. While doing this I replaced some of the inductors with Jensen copper foil air core inductors (0.16 mH and 0.25 mH) and most of the resistors with paralleled 2W Riken Ohm carbon resistors. (I can do this because my amplifier is low powered).



    This is all I have done so far. I might replace the rest of the capacitors and inductors in the near future and the L-pads will definitely have to go. So far the improvements have been worth the effort. The biggest improvement has been the replacement of the nasty yellow caps in the stock crossover. These caps are easy to replace and it makes a very big improvement in sound quality - start with those.

  15. #15
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    I have never gotten around doing anything about the 52 uF capacitor originally discussed in this thread. I have found a couple of possible replacements, but I am no longer so sure that the original 52 uF cap used is all that bad, although it annoys me that so much of the signal has to pass it. In my version of the crossover the 52 uF cap is bypassed by a 4 uF cap, and this cap I replaced with a Jensen Paper in Oil capacitor (Old paper in oil type in metal can).



    I chose to use the Jensen Paper in Oil caps in metal cans because I know these well, and I really like the sound. I have never tried Hovlands in my crossover so I canít comment on those.



    I chose to use Riken resistors in my crossover because I find they sound very nice in most applications. I also like the sound of Allen Bradley Carbon comp, but they are getting harder to find in 2W versions, and the values tend to drift a lot over time. Some people doesnít like the sound of carbon comp resistors, but I find them more natural sounding than any other type I have tried.



    So far I havenít made any changes to the crossover circuit, although I would still like to simplify it a little.



    I would very much like to know more about the results of your experiments, so please keep us posted.

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