The N2400 Revealed

[Baron030]

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

[Baron030]

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

[spkrman57]

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

Regards, Ron

[Titanium Dome]

Great pictures, too. Right up my alley.

[scott fitlin]

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!

[John]

Nice thread! Thanks for sharing.

[wmckee]

Baron 030,

Thanks, that did clear everything up. I could not see the second resistor wire (blue arrow) in the photo -- it looked like a shadow of the wire indicated by the red arrow to me. Plus the wire indicated by the red arrow looked a little like a twisted pair. Thanks again for taking the time for such a detailed explanation.

Walt

[grumpy]

good info... had to rib you at least a little.

[2turbos]

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.

[wmckee]

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

[Baron030]

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

[Baron030]

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

[spaceholder]

Hello everyone, I'm in the process of building these x-overs for a pair of 030s that I bought. I'm a bit of a newbie at reading schematics and am not sure I have gotten all the connections right. I have, by the way, I looked at all the pictures of other people's builds, and they have been a big help.

I'm hoping that Baron or anyone else familiar with these crossovers would look at my pictures and tell me if I am on the right track.

.

I realize this is an old thread, but it seems to be becoming a useful resource these rebuilds, if mods think this should be a new thread just let me know.

Edit: I can't seem to figure out how to rotate the pics, anyone have a hint?

[Baron030]

Hi
One picture can say a thousand words. So, I used Microsoft Paint modify one of your pics.
Hope this helps.



Baron030

[audiomagnate]

What do the little x's and the dotted lines mean in this schematic? I know how to read a schematic but this one confuses me.