Charge Coupled Crossover Upgrade - JBL S4800

This is my first post here and I wanted to participate and contribute back to the community as I have been lurking for a long time when making my purchase/upgrade decisions to switch to JBL. I have been building/tinkering with speakers for many years now and came across my first pair of serious JBL’s last year in the form of S4800’s. They provided me with a great listening experience over the last year and helped remove me from the troubles of the world.

I spent a significant time listening to them, and always wondered can they be better? I thought about upgrading to Be diaphragms, switching to active crossovers, etc. and figured I would first try to charge couple them as I have never experienced a CC’ed network.

My primary goals for the modifications were to:

1. Minimally impact the external appearance/build quality of the speakers
2. Dampen the cabinets better
3. Charge couple/upgrade the networks without having to completely rebuild the boards/make new boards
4. Make the speakers sound better for a reasonable cost

I used Solen fast caps in place of the OEM 100 VDC yellow cheese capacitors. I determined there was enough space to mount them vertically in all locations and re-use the existing PCB’s. Hot glue/zip ties were used to affix the capacitors and I find that this mounting is sufficient for home use without risk of damage to the networks. I wired the charging resistors point to point as if on a tube amp. I also used A23 12v batteries instead of the usual 9v because they are smaller, and provide a slightly higher biasing voltage. A separate battery is used for each network LF and HF/UHF to permit biamping in the future. The batteries are mounted with Velcro inside the speaker directly in front of the port tube, it is easy to reach in and change them.

While the speakers were apart I determined that one of the internal windowpane braces was not glued on the front baffle side from the factory (it rattled if you knocked on it). I had to implement a strategy to remedy this – I decided to cut small wood wedges and use them to pretension the brace.

Sonic barrier 3 layer damping was applied behind the woofer to the back and sides. The original 1” fiberglass was reused and the bottom chamber were damped with some 1” thick denim insulation.

My overall impression after the modifications is very positive. My original impression was always fantastic, the speakers handled many different genres and qualities of recordings without becoming too revealing, or fatiguing. After the modifications the bass is tighter, fast drum patters are more distinguishable. The charge coupling seems to have improved the transient response and individual musical notes are more strongly defined (cymbals have the most pronounced effect.

I am extremely pleased with the ~$200 in modifications, as they have elevated the performance of the speakers to a level that is much more enjoyable. I am convinced that charge coupling provides a positive benefit.

OEM HF/UHF network
Attachment 88250

OEM LF Network
Attachment 88251

Upgraded LF and HF/UHF networks
Attachment 88249

Upgraded HF/UHF network showing charging resistors point to point wired
Attachment 88252

S4800 makes a great speaker stand (temporary listening setup while I was working on the JBL's)
Attachment 88254

Welcome to the forum and thanks for sharing your work. Also good catch on the brace not being glued.

Quote:

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Originally Posted by dustybottle

A separate battery is used for each network LF and HF/UHF to permit biamping in the future. The batteries are mounted with Velcro inside the speaker directly in front of the port tube, it is easy to reach in and change them.

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Cool idea and great work on the networks!

I assume the port is large enough to get your hand inside and short enough to allow some dexterity? Reminds me it's time to change the batteries in my 4345 CC crossovers. Since they are clones, I used bi-wire banana terminal inserts and the battery is on the crossover mounted in the bottom of the boxes. I have to remove the 4-screws holding the input cups to get to them, but it's pretty simple.

Quote:

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Originally Posted by BMWCCA

Cool idea and great work on the networks!

I assume the port is large enough to get your hand inside and short enough to allow some dexterity? Reminds me it's time to change the batteries in my 4345 CC crossovers. Since they are clones, I used bi-wire banana terminal inserts and the battery is on the crossover mounted in the bottom of the boxes. I have to remove the 4-screws holding the input cups to get to them, but it's pretty simple.

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The port is 4" diameter and the speaker interior is only about 9 in. deep, so it is simple to reach in and change the batteries. The batteries are mounted directly in front of the port, you can see them if you look in, with the velcro mount you can pull out the battery assembly. I thought about mounting them behind the input plate, there was room for that but decided against it. I tend to overthink things and make them more complicated than they need to be...my friend gave me the velcro idea.


I will check the voltage on the batteries in a few months and see how much juice is left.

When you change your batteries if you have a multi-meter, measure the voltage. Would be interesting to know how long they have been installed, and how much charge remains.

Hey, Welcome to the Forum!

I am not to sure how much research you did before undertaking such an upgrade as "Charge Coupling" but I would like you to do some more looking at

diagrams of JBL CC'd Networks before taking another look at your actual wiring up. You may even find that there is a little more to it...

Off the top of my head the JBL 4344 MkII is one example. Easy enough to google for the Technical Manual which has lots of info plus the Schematic.

Hope you find this beneficial. Questions are always another way for Help if needed! Forum members will usually be glad to help!

Kind Regards,
DogBox
[Steve]

Dear Steve, thank you for the reference info I did not consider the 4344 mkII design, but after reviewing the schematics my implementation is the same. I did extensive research on existing JBL designs and the pros/cons of CC crossover networks before implementing including reading everything GT has written about them. The network works as intended as verified through verification of DC biasing voltage at capacitor junctions, with no DC passed to speaker/amplifier. I based the modifications on the JBL S5800 schematics and the S9800/S9900 schematics to ensure that my plan was solid. The results speak for themselves in my application, this was a very worthwhile improvement. The frequency response curve has also been verified to be similar through measurement of the speakers in room at the same positions they were. The overall freq response curve is very similar, but music is more enjoyable. Cymbals/drums especially sound much more realistic than before the implementation.

Quote:

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Originally Posted by DogBox

Hey, Welcome to the Forum!

I am not to sure how much research you did before undertaking such an upgrade as "Charge Coupling" but I would like you to do some more looking at

diagrams of JBL CC'd Networks before taking another look at your actual wiring up. You may even find that there is a little more to it...

Off the top of my head the JBL 4344 MkII is one example. Easy enough to google for the Technical Manual which has lots of info plus the Schematic.

Hope you find this beneficial. Questions are always another way for Help if needed! Forum members will usually be glad to help!

Kind Regards,
DogBox
[Steve]

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Hi Dustybottle,

Glad you are hearing the benefits of your work! :)

I was just not familiar with how you achieved your success. Hope this inspires you for the future!

Kind Regards,
Steve

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