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Thread: stock 4345 crossover 3145 schematic

  1. #16
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    Quote Originally Posted by ivica View Post
    concerning the original 3145 and later comments from Mr. G Timber
    http://www.audioheritage.org/vbullet...l=1#post110075

    "....The second problem is the use of a passive crossover between the top of the woofer and the bottom of the 10". Passive crossovers set to frequencies below about 500 Hz react badly with the motional impedance of the woofer/box combination and give substantial gain around 100 Hz. Gain out of a passive system is generally a bad thing. In the case of the High Pass, we have to work the passive network through a really large motional impedance peak resulting from the 10" fundamental resonance in the sub enclosure. This means that the actual voltage drive that occurs at the terminals of the 10" is less than ideal....."

    I have tried to get some improvements in 2245/2122 cross-point. From the simulation I have get that using 'Impedance compensation network, and kind of resonance -peak compensation", upper mentioned "lack" of 3145 can be improved, reducing mentioned "100Hz-peak and resonance interference " better then 3dB, but the complexity of the network has rised.
    A system of this caliber should have been bi-amp only like the 4340, 4350 and 4355...

  2. #17
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    Quote Originally Posted by santashooter View Post
    So you would be able to take the CC networks (as posted numerous places on this forum) and remove the double caps with a single of half value and then you wouldn't need the battery?
    how are peoples thoughts about the sound of these.
    I would like to go all passive, but if i could achieve the same SPL with a passive network instead of a CC i might consider that.

    best regards
    Soren
    Yes, you end up with a circuit essentially the same as the original production circuit sans the tapped coil (thank you Dr. G!). I went this way because I wanted to try some circuit tweaks since my drivers are non-standard. A lot easier to modify without the cc double caps! Surprised how good it sounds as is (old ears!) Mike

  3. #18
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    Quote Originally Posted by Mannermusic View Post
    Yes, you end up with a circuit essentially the same as the original production circuit sans the tapped coil (thank you Dr. G!). I went this way because I wanted to try some circuit tweaks since my drivers are non-standard. A lot easier to modify without the cc double caps! Surprised how good it sounds as is (old ears!) Mike

    Hi guys,

    Please excuse my ignorance, but if not wanting to cc the passive crossover is as simple as removing the dc battery and halving the cap value (which is a good thing?), what is the point of designing the CC version in the first place?

    Being quite a beginner in passive crossovers, I'm still trying to get my head around what I should be doing for my '4345 build' too. If possible, I'd prefer not to use batteries.. do want to run bi-amped though.

    Cheers,
    Tuyen

  4. #19
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    Quote Originally Posted by tuyen View Post
    I'd prefer not to use batteries..
    Use the diode method instead.

    Example:
    Attached Images Attached Images  

  5. #20
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    Quote Originally Posted by 4313B View Post
    Use the diode method instead.
    A very elegant solution IMHO.

  6. #21
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    what the?! that looks really complicated!? hrmmm.. okay now I'm really confused. lol

  7. #22
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    Let's say you have a 4 uF capacitor in series with an 044 in an L96.

    Replace the 4 uF capacitor with two 8 uF capacitors in series.
    Between the two 8 uF capacitors in series place a 10k resistor and a 1N4935 diode.
    Connect the cathode of the diode to the red input of the network.


    what is the point of designing the CC version in the first place
    What's the point in spending more than a couple hundred bucks on an amp?



    JBL has taken biased passive filters to the next level. The technology is employed in the new JBL M2.

  8. #23
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    Thanks mate. I sort of get it now.

    I will try follow and build the bi-amped CC passive design as outlined in previous threads.

    Probably need to first figure out what changes are needed to run the combination of drivers that I have.

    JBL 2245H 8ohm, JBL 2122H 8ohm, JBL 2470 with factory tit diaphragms + Radian 1225-16ohm alu drivers + 2307 horn, JBL 2405 with factory (8ohm?) blue jbl diaphragms.


    I would like to eventually change (upgrade?) to 2445J with truextent diaphragms (with suitable 2311 horn) when the opportunately arises. Sometime after when I have things running okay.


    Cheers,
    Tuyen

  9. #24
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    Quote Originally Posted by tuyen View Post
    I would like to eventually change (upgrade?) to 2445J with truextent diaphragms (with suitable 2311 horn) when the opportunately arises. Sometime after when I have things running okay.
    Tuyen, are your cabs finished? Do they follow the original plans?

    A 2445 will never fit in an original 4345. A 2440/2441 is borderline, it contacts the midbass box. If you want a safe bet for a 4" driver, look for a 245x.

  10. #25
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    Hi Joe,

    Not started the build yet mate. I would be okay distancing the midhigh driver position slightly out to cater for future 244x driver? Not quite sure how big the 244x is.

    The reality is that my povo 2245h/2122h drivers aren't using original jbl recones anyway, so I'll never achieve the genuine '4345 sound', thus my thinking was that there is not huge point for me to try keep exact to original 4345 cab plans.. I'm favoring the general driver layout of this diy 4345 (bass ports along side the woofer).

    Name:  4345 Mk II 10.jpg
Views: 1721
Size:  77.6 KB

    You guys have any thoughts on my approach?

  11. #26
    Senior Member just4kinks's Avatar
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    2445 is 9 1/4" diameter, 4 5/8" radius.

    In the original 4345 design, the horn axis is 3 3/8" from the top of the midbass box, and 4" from the top panel of the 4345 (not including the bracing). So you would probably end up making the entire cabinet taller to make everything fit.

    2441 is 7" diameter, only 1/8" (in radius) too large. You could probably make it fit, but your 2311 might not seat properly.

    TAD TD4001 is ~6 3/4" diameter. 2450 is ~6 1/2".

    When I built my cabs, I redesigned for an 8" diameter driver by sloping the midbass box. 4313B did something similar in his build (I think that might be the picture you posted....?).



    As far as baffle modification goes, my $.02 is to stick with the original. Baffle layout is more than cosmetic, and with a time-tested design like the 4345 it's a lot easier to screw it up than to improve upon it.

  12. #27
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    Seems like I've hijacked the thread, so I might as well keep going.

    Thanks Joe. Yep, that is a photo of 4313B's '4345 diy' project. I'll attempt to do the same thing when building the enclosure for the 2122H driver.

    A change to the 2441 seems okay if I was factor in the slope.


    Taken your advice on-board. Will stick to original baffle layout!


    Back to the topic of crossovers for 4345s, any clues where I can find suitable l-pads needed for the bi-amped cc xo? finding the right caps, resistors and coils is easy enough.

    Cheers guys,
    Tuyen

  13. #28
    Senior Member ivica's Avatar
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    Quote Originally Posted by 4313B View Post
    Use the diode method instead.

    Example:
    I would suggest for D1, D2 some lower voltage drop diode such as MBR160, even there would be about 0.2V to 0.3V minimal signal amplitude to be applied to produced polarization voltage. Such level with 93dB/1W/1m sensitivity speakers would produce about 70dB SPL.

    Regards
    Ivica

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  15. #30
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    Quote Originally Posted by ivica View Post
    I would suggest for D1, D2 some lower voltage drop diode such as MBR160, even there would be about 0.2V to 0.3V minimal signal amplitude to be applied to produced polarization voltage. Such level with 93dB/1W/1m sensitivity speakers would produce about 70dB SPL.

    Regards
    Ivica
    An Intriguing Recommendation Ivica !

    The Schottky diode (in some respects ) is superior to the standard silicon-junction based types ( ie; most importantly in voltage drop & recovery speed ) .

    Unfortunately, it's specs are inferior in the following areas ( the reverse leakage current spec might be the deal breaker for me ) ;

    Quote Originally Posted by Wikipedia
    Limitations

    The most evident limitations of Schottky diodes are the relatively low reverse voltage ratings for silicon-metal Schottky diodes, typically 50 V and below, and a relatively high reverse leakage current. Some higher-voltage designs are available; 200V is considered a high reverse voltage. Reverse leakage current, because it increases with temperature, leads to a thermal instability issue. This often limits the useful reverse voltage to well below the actual rating.
    While higher reverse voltages are achievable, they would be accompanied by higher forward voltage drops, comparable to other types; such a Schottky diode would have no advantage [3] unless great switching speed is required.


    - Apparently I'm one of the few ( on this forum anyways ) that can hear the deleterious effects caused by the battery within the bias circuit ( it drove me nuts I must say / sounding like someone had lightly touched the diaphragm with a "phantom finger" ) . I ended up disconnecting the battery after the caps where fully "formed" ( & then would let the caps slowly float/deflate as the AC beat up on the DC, before eventually rebiasing ) .

    - I'll need to try both ( types of diodes ) to see if there's an apparent sonic difference .

    Thanks for the suggestion !


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