• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Charge-Coupled JBL 4435 Networks

Zonker92

Zonker92

All shiny and chrome
Just finished one board: My goal was to have plug-and-play biased networks that I can drop into 4435s and keep the existing wiring harnesses and rheostat / L pad. No cut wires; easy battery access; fully reversible; all stock attachment points/fasteners.

Basically, I (1) mounted the caps off the PC board on an MDF panel; (2) upgraded L2 to an air core (same DCR; aluminum screw in the middle); (3) upgraded the resistors; and (4) bypassed the biamp switch while breaking out the LF and HF inputs.

So ...

C3 (15 uF) in parallel with C13 (15 uF) = 30 uF x 2 = 60 uF - two in series. Daytons.

C11 (12 uF) x 2 = 24 uF (I used two 12 uF in parallel) - two in series. Jantzen cross caps.

C9 (2.5 uF) x 2 = 5 uF (I used 4.7uF in parallel with 0.3 uF) - two in series. Audyns and Jantzen Standards.

I wound up replacing all the resistors with Mills 12-watters from Parts Connexion. Using four 62-ohm resistors in the R6 - R9 positions preserved and enhanced the power-handling capacity of the LF circuit. I replaced the L2 1.0 mH inductor with a Jantzen air core from Parts Express; 16 gauge I think was the right DCR. I left the smallest (L1) inductor in place as it's already a nice air core. I also left intact the bigger coils on the woofers (L101 and L102) on the assumption that they do a decent job by all accounts, although I'd probably use Erse Super Qs if I replaced them, and try to match the DCR.

I won't know how it sounds until I get these bad boys back together. I might throw in some bypass caps before I button them up.

(PS In hindsight, I could have just put everything on a new board, fresh, but this way seemed simpler at the time, especially since I wanted to reuse the Faston connection approach that the PC board uses.)

DSC_6588.jpg

attachment.php

DSC_6613-001.jpg

DSC_6620-001.jpg
attachment.php


attachment.php


(PS I had the connections for L102 and L102 reversed in the picture; fixed now)
 

Attachments

Last edited:
Register to hide this ad
Thanks! Silly I know, but I'm proud of the way I located the battery holder, and also I thought of a neat trick with the zip ties: I sank one end into a recess, then cut off the ratchet from another and zipped it down into another recess. :D
 
Last edited:
Interesting.
I know very little about crossovers, outside what a capacitor does in a simple first order.
 
I wound up removing the AL screw in the coil, just to be sure it didn't mess with the inductance. And I had the two big iron cores connected to the wrong points; I switched them. I also added Audiocap Theta bypass caps.
 
Last edited:
Nice work! As you know I am in the process of modifying my 4435 crossovers and much less experienced than you. I wasn't considering charge coupled networks until you showed us your latest creation, thanks a lot:-) Can you explain the pros and cons of converting to a charge coupled biased network?
 
Thanks!

Pros: It's supposed to sound better; see here:

http://www.audiokarma.org/forums/showthread.php?p=8491569#post8491569

I understand that the end result is that for most volumes, the alternating current stays above the zero point, reducing the distortion that results from it going back and forth through zero. I tried it on some L20Ts; see here:

http://www.audiokarma.org/forums/showthread.php?p=6609979#post6609979

They sounded fantastic. I have not finished the 4435 build yet so I can't say how I like it.

Cons: Expense, complexity, size, weight, and volume (which I've arguably listed in decreasing order of significance), plus you need to change the batteries every so often; around their expiration date.

Specifically, you need to double each cap's value, then put two caps, each of that doubled value, in series, in place of the original cap. (The resulting capacitance is the same as the original). This allows you to introduce a charge in the "middle" of the capacitors, which would be impossible with a single cap: At the junction of the two doubled caps you connect, through a 3 (or so) megohm resistor, a +9VDC wire coming off your battery. Then connect the negative battery terminal to the crossover's negative terminal.

Here is a simple drawing of the general concept:

attachment.php


(I think if you read down you'll see I read one value wrong; it was 8 uF not 6, so it should be two 16s in series.)

And see http://www.audiokarma.org/forums/showthread.php?p=8483745#post8483745

That's pretty much it. I ran one +9VDC wire to each crossover junction (through a separate resistor for each connection), and one negative battery wire to each of my (now split up) LF and HF circuit's negative terminals.
 
Last edited:
Those particular caps weren't too (too) bad; I didn't go for the really spendy ones. We're moving into a new house next week and I'm leaving the 4435s in pieces until after the move; much safer and easier to lift and carry the empty cabinets.
 
I ordered mills resistors and Janzen air core coil from Parts Express but they did not have the 62ohm resistors. Any idea where I can buy them.
Good luck with the move.
 
Thanks! Parts Connexion is the place for most of the Mills resistors; Parts Express has fewer values.
 
I bought my 4435's about a month ago. One owner, he used them for home use. When I took the grills off they still had the tags on them. Veneer has one water spot about 2"x2", other wise in nice shape. Just needs to be oiled. Original grill fabric has several small snags from a cat but not noticeable unless you are close. He had the all the 15"s reconed with factory jbl cones about 10 years ago. Surrounds need to be replaced again. They are still intact but very soft and fragile. I have just replace two of them. I was a little disappointed with the sound so I am going through every thing trying to make improvements. The speakers are lacking bass and just do not have the sound I was hoping for. Although some recordings do sound pretty good, most do not. Sent my Mcintosh c30 preamp and Mcintosh 7270 amp into the shop to get checked out and now replacing every thing on the crossover boards except L1 coil. I did find one bad cap on one of the crossovers (c11). The rest of the components seem to be in spec. Hoping to get some improvements with bypassing the switch and upgraded components as follows; Mills 12W resistors, Jantzen Cross caps with Russian K40Y-9 paper in oil .01uf bypass caps and Jensen Foil coil air core for L2. If you have good results with your Charged coupled networks. I may do the same. That is why I started with inexpensive caps.
My room is not great for acoustics, open living floor plan, Partial side wall on left side, wood floors, 10' ceiling. We are in the process of moving into this new place so a lot of new variables to deal with. I should have crossover parts in about a week. I will keep you posted as things progress. Any suggestion are appreciated.
Thanks for all if the information, it has been very helpful!!!
Scott
 
Interesting, Scott; thanks for the 411. Sounds like a great pair to be working with. If your experience is anything like what I had with my 4430s, bypassing that switch will be like turning on the lights in a dark room. The LF woofer doesn't run through that switch, but the MF does, and it does a great deal of the upper bass work, and the midrange. I'm guessing you're planning also to clean up the adjustment "pots?"

I'm very much looking forward to hearing mine, too. We're in the middle of our move right now but it may be a week or two yet. (We're moving gradually.)
 
The L pads did not produce any static when turned but I also did not hear much change either. I need to clean them but not sure what the best way is. I have not seen an easy way to pull them out. I am afraid to separate the plate from the face of the speaker. I will probably try to clean them in place. What is your recommended cleaning method, and what brand cleaner do you use? Not sure if some of the cleaners may attack the old plastic. From my experience alcohol makes some rubber and plastics brittle.

Thanks,
Scott
 
You must log in or register to reply here.
Back
Top Bottom