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Thread: The N2400 Revealed

  1. #1
    Senior Member Baron030's Avatar
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    The N2400 Revealed

    I am currently restoring my old 030 systems. So, I thought I would take the extra time to document a few things. The N2400 crossovers pictured below were purchased in 1973 for $23.00 each and have serial numbers of 37510 and 38634. Since, the L-Pads were in really bad shape, I decided I would open up the boxes and inspect everything. To open the boxes, the heads of 4 rivets were very carefully drilled off. This allowed the back covers to be removed. Upon inspection, I turned up a few surprises. First, I was surprised by just how small the coils were in size, with only 20 gauge wire. Second, the coils had a different part number, then what was described in N2400 circuit schematic. So, I have revised the N2400 schematic below to show the differences that I found. Also worth noting in the #38634 N2400 crossover, the 5 ohms were 10 watt instead of the 11 watt size. The pictures below are of the #37510 N2400 crossover, which has the larger 11 watt resistors. In testing the N2400 crossovers, the #10421 coils had inductance values of 1.057mH and 0.997mH and all of the #10296 caps had values that varied between 6.1uF and 6.2uF of capacitance. Considering that the caps are 36 year old, I am pleasantly surprised by how well they have held up.
    Baron030
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    Senior Member Baron030's Avatar
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    The N2400 Overhauled

    Since, I am turning my old 030 system over to my nephew, who is not very knowledgeable when it comes to electronics. I decided to replace a lot of the components. This would keep the old 030 system fairly trouble free for a really long time. Part Express had all of the parts that I needed. Their 15-watt mono L-Pads are an exact replacement for the JBL originals. And I decided to upgrade the #10421 JBL coils with 1.0mH - 18 Gauge Laminated I Core Inductors. And even though the #10296 JBL caps were in really good shape, I opted to replace each of them with 2 3.0uF Solen caps and a 0.01uF Theta AudioCap. After completely overhauling one of the crossovers, I did a side by side comparison. The crossover with the new components did sound a lot better. The 075s sounded slightly cleaner with the bypassed Solens. But, the most dramatic improvement was with the D/E130s, particularly at higher volume levels. I really think that the #10421 JBL coils are saturating and creating some distortion. So, the larger I Cores are a real improvement. Finally, to reinstall the original back cover, I first drilled out the old rivets and then tapped the holes to accept 6-32 screws.
    Baron030
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  3. #3
    Senior Member spkrman57's Avatar
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    Thanks for sharing with us...

    There are a few vintage fans amongst us who still play with the vintage older 2-way systems.

    Regards, Ron
    JBL Pro for home use!

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    Nice Job

    Great pictures, too. Right up my alley.
    Out.

  5. #5
    RIP 2010 scott fitlin's Avatar
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    Hey, thats really cool. Your nephew should indeed be very happy with his new JBL,s and quite grateful to have such a super uncle!

    scottyj

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    Nice thread! Thanks for sharing.

  7. #7
    Senior Member glen's Avatar
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    Very nice reveal indeed Baron!
    Thanks a lot for the detailed info and great photos.
    glen

    "Make it sound like dinosaurs eating cars"
    - Nick Lowe, while producing Elvis Costello

  8. #8
    Junior Member fecooper's Avatar
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    Thanks, Baron

    You inspired me to bid on and win a couple JBL N2400 crossovers on e-bay which I then took apart and replaced the capacitors and resistors (did not replace inductor) as you did and put them back together. I used "pop" rivets (worked great) instead of threading the box. My speaker system consists of D-130 woofers and LE20 tweeters. Everything sounds great. I made one small change to the crossovers - I used a 4 ohm (series resistor) and an 8 ohm (parallel resistor) instead of two fives. I wanted a little more volume to my tweeter. I don't believe the LE20s are as efficient as the 075s (which I hope to get someday). With the fader control, I have enough range to make the adjustment.

    Thanks for the inspiration to jump in and modify a JBL crossover.

  9. #9
    Senior Member Baron030's Avatar
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    Well, I can see that this is your first posting here.
    So, welcome to the LH forums.
    Im glad that I could be of some help around here.

    Baron030

  10. #10
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    Quote Originally Posted by Baron030 View Post
    Since, I am turning my old 030 system over to my nephew, who is not very knowledgeable when it comes to electronics. I decided to replace a lot of the components. This would keep the old 030 system fairly trouble free for a really long time. Part Express had all of the parts that I needed. Their 15-watt mono L-Pads are an exact replacement for the JBL originals. And I decided to upgrade the #10421 JBL coils with 1.0mH - 18 Gauge Laminated I Core Inductors. And even though the #10296 JBL caps were in really good shape, I opted to replace each of them with 2 3.0uF Solen caps and a 0.01uF Theta AudioCap. After completely overhauling one of the crossovers, I did a side by side comparison. The crossover with the new components did sound a lot better. The 075s sounded slightly cleaner with the bypassed Solens. But, the most dramatic improvement was with the D/E130s, particularly at higher volume levels. I really think that the #10421 JBL coils are saturating and creating some distortion. So, the larger I Cores are a real improvement. Finally, to reinstall the original back cover, I first drilled out the old rivets and then tapped the holes to accept 6-32 screws.
    Baron030
    I followed what you did and scratch built a set of these crossovers for my D-123/075 rehab of my Dad's 50's speaker system. His crossovers were 1st order and the Hf would distort as there was no adjustment pad for the 075. The 5 ohm resistor update might have been a big help.
    Thanks for the thread Baron 030, it was a nice piece of research.

  11. #11
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    Question Photo of wiring diagram

    It appears from the photo of the upgrade of the N2400 crossover that the resister bridge is not wired per the the original JBL schematic. Granted, the pictures do not show everything, but it looks like the two 5 ohm resistors from the L-Pad <red wire> do not go to <black> and <capacitor-red> respectively, but are both twisted together and probably go to <capacitor-red> with nothing going to <black>. This would actually work and approximate the protective additional resistance that JBL wanted to use to protect the 075.

    First, is my observation correct? Second, was this done on purpose and, if so, why?

    Otherwise, a fantastic job of documenting this N2400 upgrade, which I am in the process of implementing myself.

    Thanks, Walt

  12. #12
    Senior Member Baron030's Avatar
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    Hi Walt
    The pictures may not look right to you. But, I can assure you that the networks were rebuilt correctly to JBL specs and that they follow the schematic that I posted perfectly. The purpose of the two 5 ohm resistors is to create a -8.5db, fixed L-PAD network. This limits the maximum setting of the variable L-PAD network to prevent damage to the 075 driver. I suspect that before JBL added the two 5 ohm resistors, they had service issues with careless 030 system users.

    Baron030

  13. #13
    Senior Member Baron030's Avatar
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    Hi Walt

    I just had a thought as to why you might think that the L-Pads pictured were not wired up correctly. In the re-build, I used 15 watt Dayton L-Pads. The Dayton L-Pads may have a different pin layout then the original JBL #10285 L-Pads. So, if you are going to use Dayton L-Pads, then follow their instructions and schematic that comes with their pads. Otherwise, you may not get them wired correctly in the network.

    Baron030

  14. #14
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    Schematic Photo

    Baron030,

    The question was not about the L-Pad (I used the generic Parts-Express one), only the two 5 ohm resistor bridge itself and where the ends of the bridge connect to regarding the rest of the circuit. I am trying to attach a JPG showing what confused me. I was sure I had it wrong but still wanted to ask -- it just looked like the end-points of the bridge (unlike the schematic) were twisted together in the photo.

    Walt
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  15. #15
    Senior Member Baron030's Avatar
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    Hi Walt
    The picture you posted has the coil covering a solder lug terminal. I magnified the pervious photo where the coil has not been installed yet. Now its hard to see but there are two resistors stacked on top of each other. I have highlighted the same wire that you are talking about with red arrows and the other connections are color coded in blue, green and cyan. And I have highlighted the same connection points on the schematic. I am not sure if this helps clears things up or not.
    Baron030
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