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Thread: Jbl 4425 crossover layout

  1. #1
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    Jbl 4425 crossover layout

    Here it's JBL 4425 CROSSOVER LAYOUT
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    Junior Member LarryM's Avatar
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    4025 Layout error

    R1 and R2 are not connected right. Node E4 should run through to E5. You have R1,R2 in series with E4 and E5, which is incorrect. C1,C2,R1,R2 should all be in parallel (All parts across E4,E5 to E2,E6).

    And L1 is spun from very fine wire in order to have 7.5 ohms of resistance. If you are using the stock JBL coil, your ok. It would be made correctly. If you are buying a coil to use in its place, you will need to add a resistor in series with L1 to get a total of 7.5 ohms (L1 resistance + resistor) Most any 1.0mH air-core coil has about .3 to .5 ohms resistance from 18 to 22 ga wire, unless it is made from really fine wire.

    Looks like a nice layout.

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    I saw the mistake, mea culpa. Will made the correction for R1/R2.
    Both coils will made by myself. In Romania JBL spare parts very hard to find.
    For L1 I can do air core coil, ferrite core coil or laminated "I" core coil.
    Which it's the best in this case. What wire size?
    For L2 what's the transformer section and what wire size ?

    Thank you

  4. #4
    Junior Member LarryM's Avatar
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    4425 Layout

    Layout:
    Good, R1,R2 will be fixed. One thing to ask; are you making a PCB layout with etched copper? Or just running wire on a piece of fiberglass or wood? If you are running wire, use at least 16ga wire for the woofer and ground traces. If you are etching copper, think about this. 1 oz copper on a single sided PCB is only .00137 inch thick. It takes about 1.5" wide trace to equal a 16ga wire, which has .00203 sq in area. This is really difficult to do on a PCB. Crossovers, particularly for high-power woofers really need larger traces or tracks to get good low impedance connections. If you cannot get the width of tracks you need, just run a piece of bare 16ga wire on top of the tracks where you need the power (ground and woofer) Even the horn section of the crossover should have .5 inch wide traces too. If you are laying out a PCB, try to get a double-sided copper board. That will double your copper track width. Etching those is more difficult though. I have a 1400 SAM1HF array horn with the crossover PCB, big tracks, double-sided. Unsoldering parts was hell, took lots of heat and had to heat-sink the components to protect them from over-heating.

    Your coils:
    L2, 3.8mH. Forget air-core. You would need heavy wire, 14ga and lots of it. Cost would be high and one big heavy chunk of copper, also resistance would be too high. Try to get a laminated core with at least 16ga wire. You will get low ohms (less than .4) and not so much wire required. Make sure the core can handle the watts (250 or 500 would be better) Do not use a small core or it may saturate with high power and distort sound. Can you buy one? That would be more simple and probably less expensive than making your own.

    L1,1.0mH, 7.5 ohm. If you can, get the smallest ga air-core you can get. It will be much smaller in size and less expensive. The JBL coil, in my estimation, is made from 30ga or smaller wire and takes 300 or more turns to get 1mH at 7.5 ohm. If you do make your own get fine wire like 30ga and wind till you get about 1.1mH, cut the wire and then measure again. Remove wire until you get 1mH. Do it this way. If you wind to exactly 1mH with a long piece of extra wire and then cut it, it will then be less than 1mH. The long straight wire does have inductance too. It is easier to unwind than to add them. No matter how you make/buy the coil, add a 1 or 2 watt resistor in series with the coil. Measure the coil resistance of L1 and add the R needed to get a 7.5 ohm total. Some meters don't like measuring resistance of inductors, keep that in mind. Be sure to subtract the resistance of your meter leads. Hook the ends of the meter leads together and check the value, it will likely be higher than the coil resistance your measuring, especially with coils less than 1 ohm. Work the lead plugs and scrape them a bit to get the lowest resistance. Subtract the lead resistance value from the coil reading. Many techs forget about doing this.

    Good luck,

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    Thank you Larry M for quick answer.
    Crossover final layout it's here.
    As you said the best solution it's to build the crossover "on air" with thin wood piece as support.
    I will do that and will run wire. Will look like turret (from tube amplifier).
    16ga wire mean 1,31 mmsq so I'll use 2,5 mmsq for the ground and low frequency
    and 1,5 mmsq for the high frequency.
    Have a question in here. Resistors and capacitors in this crossover have not all 16ga thick pins
    .

    Why must use 16ga or larger wire if their pins can not handle the same current as 16ga can do?
    Thank you also for the very precious informations about coils.
    I like coils. I like to build. I am also hamradio.
    see my page http://www.qsl.net/yo4fng/

    Keep in touch,

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  6. #6
    Junior Member LarryM's Avatar
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    Turrets would be useful for a crossover layout. The kind that are hallow inside would allow you to run the bigger gauge wire to the turrets on the back of your board. The layout would less cluttered than everything on one side. Can you swage a turret using a wood board reliably? Usually they are used with fiberglass or something harder than wood. Never tried wood.

    Some of our comments about wire size/gauge lead me to think you are working in UK SWG gauge while in the USA it's always AWG. They differ a bit. We should just stick with talking about the cross-section of the wire or area, not gauge. 1.5mm sq is good for everything as far as my opinion goes, certainly for your HF connections, while LF and ground at 2.5mm sq is certainly big enough, but may be difficult to bend and work with. I seldom use AWG 14ga (2mm sq), it is really difficult to form. Stranded wire is a bit easier, but it will fray and make messy connections. It's true the lead wires of the individual components are smaller than the major routing wires. Those components are not passing as much energy through them. Most of the energy passes from the amp inputs to the LF speaker connections and some to the HF and ground. As an example, R1 and R2 will only burn power in the LF frequencies as the crossover is set to. They help keep the impedance more stable at woofer resonance and as the frequencies go out past the crossover point. The impedance of the woofer by nature will rise at resonance and as the frequency increases to the LF crossover point, which makes the response less in control if I can put it that way. But the actual energy through the resistors is low outside of the LF frequencies. They will burn power in the bass frequencies at high volume though, hence the 10 watt values. Capacitors theoretically don't burn power, so their wire size is not so important. Inductors we have already discussed. Their resistance in the LF does waste power and amp damping factor a bit, but there is a practical limit to their wire size. Well made coils with an iron core solve that problem, although some folks believe that only air-core is the way to go. They keep copper prices high.

    The only thing I would add is: do use non-inductive resistors if you can get them. R1 and R2 could be the wire wound type since they are running at low frequencies and are in parallel. Inductors in parallel act like resistors in parallel. Having R1 and R2 equal, one could assume the total inductance would be one-half of one resistor. Most wire wound are a few uH to maybe 10 uH, which is of little concern at the low frequencies. The non-inductive are more important in the HF, especially any in series with the amp to HF output.

    Looked over your web page, looks like you enjoy electronics of all flavors.
    happy speaker building.

  7. #7
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    Have some pictures with 4425 original crossovers.
    Not see audiophile devices.
    Resistors look to me like any other power resistors.
    Are non inductive models ?
    Capacitors look the same as usually non polarized capacitors.
    Crossover was made on PCB.
    Can you help me with the device's factory names/models ?

    Thank You

    Liviu
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  8. #8
    Junior Member LarryM's Avatar
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    4425 original crossover

    I was not aware from your posts you actually had a 4425. It seems you do. I would be hesitant to alter the original crossover, especially if you might sell the speakers later. Changing the stock speaker can reduce your 4425's value. Since you already bought the caps for the CC version and are winding your own coils, all that is left are the resistors and pots.

    Yes, the resistors on the stock crossover are non-inductive. At least I know of no posts on this forum that would indicate otherwise for any JBL xover. JBL often uses custom resistor values that are very hard to find. The 100 and 20 ohm are common and should be available. The 3.9 ohm is a standard value but have more commonly seen the 4.0 ohm. You can always use a 4.0 ohm and just parallel a 156 ohm 1 watt or some combination to get your 3.9. Or just use the 4.0 ohm, it is within a few % anyway.

    The pots are likely 50 watt, 8 ohm I think. Look at yours, they may have the wattage on them. Put your R meter on the pots and check how the resistance rises/falls between the terminals as you rotate them. Then check the replacements, if you get them. They should change resistance in the same direction you rotate the pot. I know on the 4430, the pot used in 2-wire mode is similar to the 4425 R201. When I bought a pot to substitute, when rotated clockwise, the resistance went up, which is wrong for volume to increase. It so happens JBL must have had a custom pot made that operated backwards to get the clockwise decrease in resistance. If this confuses you, just check your pots and note how the resistance changes for a given rotation direction and you will be fine.

    Sorry about my spelling. The turrets are not hallow as one might say if we wish to worship them. Not that crazy yet. I meant hollow or a hole through the middle. Both spelled correctly, just wrong word chosen. The hollow turret would allow you to stick a wire through the back of the pcb so you could wire from the back. From the back, a normal solid swagged turret has no material to solder to. Just a flush rivet against the board. Having worked with turrets, I am sure you already know this.

    Your almost there.

  9. #9
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    I don't have JBL 4425. I try to build a pair of JBL4425 clone and I want to be perfect as JBL made it.
    I started with a large documentation about these speakers.
    I posted the building evolution at DIY section.
    Thanks to you LarryM, I've learned a lot of important things to keep in mind when will building.
    The Crossover will build using the items like you can see in pictures (not know how to call them in English Language)

    I find here in Romania a company who sell capacitors and non-
    inductive resistors from JANTZEN AUDIO/Denmark

    Jantzen SUPERES KNP - 10W Resistors
    TECHNICAL INFORMATION
    - Wire wound high end audio resistors
    - Resistance tolerance: 1%
    - Very low noise figure and low inductance of <0.7
    - Instant overload capacity
    - Very high heat dissipation with a small linear temperature coefficient
    - Low annual shift
    - Flame proof wrapping
    - Temperature max.: 200°C.
    - Voltage max: 1000V.:
    - Dimension: Ø8,5 x 53mm.
    - Ceramics
    - Values: 0.47 - 330.0 ohm.

    Obviously there are more expensive types of resistors but the price vs. quality ratio is very good 2,30 Euro/piece

    N36-58450 LPad 8 ohm 30W

    I find here http://www.audioalchemy.ro/filtre/rezistente.htm a very good substitute :
    (scroll the page down to see the items/prices. Sorry for Romanian Language but have a lot of pictures that help)

    LPad 8 ohm 15W. Price: 8.90 €/Buc.
    LPad 8 ohm 50W. Price: 15.94 €/Buc.
    LPad 8 ohm 100W. Preţ: 18.54 €/Buc.

    Have a single problem to this project
    Not find yet JBL 2342 horn.
    Have a friend who can reproduce the horn 1:1 as he did in the past with many hard to find, obsolete or very expensive horns.
    That's why I am looking after a pdf or a complete design with dimensions.

    Keep in touch
    Liviu

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  10. #10
    Senior Member pos's Avatar
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    Quote Originally Posted by electronicguest View Post
    Have a single problem to this project
    Not find yet JBL 2342 horn.
    Hello Liviu,
    Try looking for JBL 3678 speakers/components on the used market.

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    Thank you POS for message.
    I know that JBL 3678 use the same 2342 horn.
    About 2342 horn very few things can be found on internet.
    Unfortunately I am from Romania and a market of used speakers does not really exist.
    About JBL speakers - no way. Dreams.
    If i need something I try to buy from internet, but to buy from outside
    European Union, shipping & taxes became very very expensive, most of time taxes more expensive as items.
    A friend of mine can build this horn if I give him a model or all dimensions.
    If somebody can help me with dimensions will be perfect.

    Thank you once again
    Keep on touch,

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    Crossover in work
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    Crossover in work
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  14. #14
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    Very Cool!


  15. #15
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    Thank you Earl K
    This is final point for the moment. I am waiting for the capacitors.
    The only one item missing: 20 ohm/10W, non inductive resistor, and most of
    producers/sellers do not want to sell in Romania (my country).
    Nothing found on eBay, Aliexpres, bla, bla ...
    Can you find for me a real source to buy 4 resistors ?

    Keep in touch
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