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Thread: JBL 43xx Charged Coupled Network Boards

  1. #91
    Member VinylGroove's Avatar
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    Nov 2014
    The West
    Quote Originally Posted by Ian Mackenzie View Post
    On the 4343 l recall it was discussed but l donít have the official updated parts list or any updates to the pcb.

    I attached the above 4315 schematics for illustration purposes to identify the parts l referred to in my post. For an equivalent network those parts in the 4315 are required. They are after the L pads and ensures the network functions correctly when connected to the actual loudspeaker drivers.

    Feedback and Recommendations.

    1. I would also suggest a pcb revision so the cabling for the drivers coming from the pcb and not the L pad tab 1 and tab 2.

    2. Secondly, l would recommend the pcbs be provided with quality pre soldered crimp style tab terminals and a labeled crimp connector cable loom for connection to the L pads and from the pcb to the mid, horn and 2405 drivers.

    That way testing and disconnection of the pcb and the L pads is much easier for the constructor. Alternatively screw type terminals with spade terminals. It needs to be idiot proof so that incorrect connections by the constructor are eliminated. Labelling of supplied cables with a label maker would make it much for the constructor during installation of the crossover.

    You donít want to be looking back and forth to the instructions when installing the crossover, the cabling and the L pads.

    This would make it much simpler for the constructor to wire up the L pads and connect the drivers to the pcb using quality crimp connectors (if my understanding of pcb is correct).

    3A. Thirdly, on the size of the pcb to fit inside of the enclosures the final equivalent 4344 networks were assembled with the horn and uhf filters stacked above the mid filter board on nylon stand offs. It might not look as pretty but itís a better approach. The two split pcbs could still be used for an external crossover network. The point is the constructor is not mandated into an external crossover implementation which will not suit all situations.

    3B. For illustration in attached image is a HF & UHF filter boards below where l used nylon spacers with brass M5 screw threads as l recall. The mid filter board was mounted on top. Some cable strain relief ensures the integrity of all cable connections to the board.
    More of an option but the pcb could be set up for bi or tri wiring back to the power amp. I didnít to that in the build below but you can see an effective star ground snake to ensure currents in the filters donít migrate into the ground.

    This was a conventional network for JBL 4344mk2 clone build in Europe.

    I never thought of using Wago lever nuts for point to point wiring projects, that's a great idea.

    These inline units could be handy as well and would work anywhere there is a wire, regardless of layout. This specific one works with 12-20awg wire.
    Attached Images Attached Images  

  2. #92
    Senior Member
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    Apr 2003

    They are excellent for loudspeaker wiring

  3. #93
    Senior Member
    Join Date
    Apr 2003

    No 4. On L pads where JBL specified 16 ohm version this was done for power handling according to JBLís Mark Gander when asked by Giskard back in 1978.

    In these 4315 and 4343 lower sensitivity systems the mid and hf drivers are attenuated more by the L pads than the higher sensitivity systems like the 4345.

    For example the 4343 foilcal has 4 db of attenuation for the zero position. If the user dials back the mid range L pad another 2 db thatís a total of 6 db attenuation. So if the mid range driver was getting 50 watts with the L pad up full and you dialled back L pad to -2 db only -13.5 watts would be going to the midrange driver. The L pad would be dissipating 37.5 watts.

    Internally a loudspeaker L pad is not a simple potentiometer voltage divider. There are two separate nichrome wire element tracks for a constant impedance attenuator.

    In a 16 ohm attenuator the series element track is 16 ohms and the parallel element track is 130 ohms.

    An 8 ohm attenuator has an 8 ohm series element and a 32 ohm parallel track.

    So for the same level of attention the demands on an 8 ohm L pad are higher with the lower resistance values.

    This is because the lower resistance tracks in the 8 ohm L pad create a larger voltage drop across the element tracks where the load impedance is 8 ohms. Power dissipation = V 2 / R where V is the voltage drop and R is the resistance.

    Therefore it is not recommended to amend the L pad values in equivalent networks. Watching your new crossover network smoking at the peak of party and then fail is not good optics. In addition the existing L pads can be utilised for internal pcb installation.

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