View Full Version : Rebuild JBL Century 100's?

09-26-2011, 11:20 PM
How much benefit might I realize if I upgrade the crossover networks in a pair of otherwise good JBL Century 100's? I'm thinking of Solen caps & the like.


09-27-2011, 12:06 AM
Like putting lipstick on a pig. Collectible, yes. Good sounding? Not really.

09-27-2011, 01:16 AM
Like putting lipstick on a pig. Collectible, yes. Good sounding? Not really.

Nowhere in this typical tired bashing of the L100s do I see an answer to the OPs question..

Yes, because the crossover is probably the weakest point in the L100, upgrading it would probably give you SOME gains. However, a better option for better sound quality if you were interested would be to sell the L100s and use the $500 or so you'd get for them to purchase a pair of 4410s or 4412s. You could use the leftover cash to upgrade the crossovers in the 44XXs and you'd end up with a much better speaker than the L100 would ever be.

09-27-2011, 07:32 AM
If you want to keep your L100’s and improve the sound try this link. Troels Gravesen is one of the top do it yourself speaker/ crossover designers around. He has designed many well-regarded speakers for the DIY community. You can trust his opinion.

09-27-2011, 10:04 AM
Parts Express also has a crossover kit for the L100. It's a re-design including better parts and inductors and supposedly corrects some midrange peakiness in the original design.

I have no experience with this kit, just an FYI.

09-27-2011, 10:42 AM
Parts Express also has a crossover kit for the L100. It's a re-design including better parts and inductors and supposedly corrects some midrange peakiness in the original design.

I have no experience with this kit, just an FYI.

Ye gods, $278, and you have to assemble them!

Rex Everything
09-27-2011, 11:39 AM
Ye gods, $278, and you have to assemble them!

Heck, you can't even buy quality caps for $278....that's pretty fair depending on components used

09-27-2011, 11:51 AM
The CO in the L100 is just a capacitor and resistor. The woofer is used full open. Any good cap will do. It won't change the sound.

09-27-2011, 11:53 AM
[QUOTE=chriswhiston;5006632]Nowhere in this typical tired bashing of the L100s do I see an answer to the OPs question..

I Agree.
It buggs the hell out of me when the owner of the L100 asks for help and gets only grade school put downs.

09-27-2011, 12:03 PM
Like putting lipstick on a pig. Collectible, yes. Good sounding? Not really.

You guys need to get some new material.

09-27-2011, 12:33 PM
Some folks just seem to be alot more help around here than others.

09-27-2011, 12:37 PM
The CO in the L100 is just a capacitor and resistor. The woofer is used full open. Any good cap will do. It won't change the sound.
My L88's are like that too, woofer wide open. On the other hand, that's truly amazing for a 12" woofer, but not the best application.

This aspect of vintage JBL speakers really makes me wonder at times about their thinking, i.e. were the drivers "that good" (to JBL of course) to warrant NOT using more elaborate xovers? I read put downs a lot about other brands of speakers, yet JBL went with rather lean xovers in many early speakers. Other speaker brands would be chided for this.

09-27-2011, 04:09 PM
I recapped my 4311s with Daytons bypassed with Thetas, using the original values. It really didn't make much different to my ears. Here is a thread on that exact job, with various approaches: (4311Bs = same basic design)

The drivers and cabinets are very nice, but the crossovers are crude. I read that the L100 was following the sound of the 4311, which in turn followed the sound of the 4310, which in turn copied a popular Altec monitor, all with a peaky midrange and too gentle of a woofer rolloff. So it was apparently a deliberate choice to make them sound that way.

The Troels/Jantzen/Parts Express crossovers are supposed to be very nice, but I wish he would publish the schematics; unless you buy the kit, all you can get are ones without the values of each component.

If you don't like the sound, another good crossover upgrade is supposed to be the one here from Murphy. I plan to use this one my 4311s. A lot people plug the ports, too, for less of a hump in the bass.

09-27-2011, 07:38 PM
Some good advice here. Thank you very much for your input.

09-28-2011, 06:02 AM
BuzzK: I'm curious as to what you would hope to obtain by doing the crossover upgrade. Are your L100's in good shape as they are?

I've had two pair of 4311's, two pair of 4312's, and one pair of L100's. I've always felt that, to my ears at least, the midrange from all of these speakers was pretty good but one had to be careful with the tweeter, especially on the 4312's. As far as bass is concerned, none of them had quite enough for me.

In a last-ditch effort to get the kind of sound I was looking for, I purchased a Polk PSW-505 subwoofer and added that to one of my systems using a Yamaha receiver and a pair of 4312's. I kept all of the level controls on the speakers right at their midpoint and I did the same with the subwoofer's crossover and volume controls.

The results, at least to me, were pretty damn good! I'm very happy with this particular system and I find that I use it almost exclusively for vinyl. The midrange is still top-notch, but now I have some "warmth" to the music, especially the vocals. In combination with keeping the tweeter levels down somewhat, I find the sound to be just right for most of my vinyl. Occasionally I'll have to make a minor adjustment here or there on certain records.

The reason I bring all of this up is because, for $199 (, I improved my system to where I wished it to be with a minimum of fuss. I've always been skeptical of the crossover upgrades. Oh, I'm sure they work, and probably work well in some cases, but for "older ears," I'm not sure if one could tell much difference from the original sound of the speakers.

Just a thought.

08-06-2012, 05:46 PM
The photo here is a crossover from what I think may be the first run of the JBL L100. Put it in the oven for 20 minutes at 220 degrees (covered most of the components with a three layers of aluminum foil, leaving the cardboard tube exposed) This was just enough time and heat to melt and pour out the wax, remove the 3 components, and not harm anything. I picked up a pair of these Century Speakers for just $50. Damaged cabinets, one tweeter has a tear and only one grill cover, but am happy to get them for that. The tweeter's are just barely audible on both when wired through the crossovers. Nothing wrong with at least the one I took out so far. Hooked it up directly as well as the mid and woofer, and they all sounded at a level as one would expect. But when all are hooked up to the crossover, the tweeter is weak. The frequency controls work fine. Wiring/Electronics has always been a weak point for me, so could anyone tell me what may be the problem of the barely audible tweeters? I really do not care to invest in a new pair of crossovers. Surely JBL could not have been as negligent as some have claimed when designing this crossover. Would like to remedy the weak tweeter problem with minimum investment. Are there any credible solutions out there?

08-06-2012, 05:49 PM
Huh. That yellow film cap is too new to be from an original L100, and L100s have no coils or resistors. Also, that cardboard tube is strange. The wire gauges are unusually thick. Do you have a picture of the speaker that came from?

08-06-2012, 06:02 PM
Here are the Century Speakers from which I removed the crossover in photo in previous post. Yes, it is from a Century L100. Any suggestions on what may be wrong?

08-06-2012, 06:09 PM
Weird. I bet those crossovers are not original. Those yellow caps look to date from the 1980s.

I would test each resistor after lifting one leg of it. I would pop off the backs of the L pads and clean them with spray contact cleaner and examine them and test their resistance. I would replace both caps. And I would make sure all the connectors are shiny and tight.

Rick Vestal
08-06-2012, 06:26 PM
It's right... Poking around there's multiple people with identical components...

08-06-2012, 06:30 PM
Wow. So in the original, older L100 JBL used an entirely different and much more sophisticated crossover, with more modern film caps? I'm not saying that's impossible, but it sure is strange.

08-06-2012, 06:35 PM
Hi Zonker92 I did actually see these very same crossovers buried in the bath of wax in tube from the L100's (in another post) I searched now and could not find it. I will admit to knowing next to nothing when it comes to this. Are these 2 rectangle objects that I removed from the cardboard tube caps? I had thought of caps as battery shaped. Appreciate you responses. Thanks

08-06-2012, 06:46 PM
I'm no expert, but I'm learning more about crossovers gradually. The rectangular objects are iron-core induction coils, often used to filter out higher frequencies. So you might put a coil on a woofer as a low-pass filter. The L100s that I'm familiar with don't have them, so their woofers run full-range, and they filter out higher frequencies simply because the woofer isn't capable of vibrating that fast. It's a very crude design.

The caps on yours are the little yellow guys at the bottom (film caps) and there are ones inside the smaller cardboard tubes (probably electrolytic). The film caps last a long time but the electrolytics tend to dry out and go out of spec. Or so I've read a million times.

08-06-2012, 06:53 PM
That's a hundred times over as to what I know. Will ponder over your advice and decide. Thanks so much for taking the time and knowledge to explain to a novice on these crossovers.

08-06-2012, 06:56 PM
OK; good luck! The really suspect items to me are the caps inside those small cardboard tubes, and the L pads. The coils and the film caps and the resistors may be fine, but testing the resistors is probably a good idea. You'd need to lift one of the legs to get a correct reading.

09-15-2012, 08:16 PM
Hi Zonker92 and all others. I decided to build new crossovers for the JBL Century's. Went with the simple design you posted (see pic). My sodering is crude but I got through it. Home Depot has full quarter inch poplar which is needed so the t nuts will not protrude, and it came close to the right width so only had to make a length cut. One of the sealed L pads had some dead spots. To open it I took some channel locks and lightly put pressure all around the metal part (halfway in) in six different positions, it then came loose. Deoxit cleaned the contacts and works good as new now. To remove the old crossover's the thin metal front plate needs to be removed to get at the 4 screws. Used a thin cake decorator blade and gently pushed in a little at a time to not crease the metal too badly. Maybe a hairdryer would have loosened up the adhesive for easier removal. I ordered the four caps needed from Parts Express (just $23, shipping included) Dayton 1% Metal Poly. Tested them out directly to the tweeters and mids beforehand. They both cut down volume around 30%, and smoothed out the courseness of sound. Two of the knobs were a loose fit to the L pad shafts. A little bondo made them tight and they will still be removable.
This simple crossover build really made a difference. Smoother now and can hear the tweeters. The original was more elaborate (see pic in previous post) but apparently something went bad with them. Had reservations on doing this as wiring is not something I enjoy, but it was really not that bad as I took it a little at a time, and it was well worth it. Feel free to email me JBL Century in subject line so I don't put in spam box.

09-16-2012, 07:09 AM
just a suggestion ...replace the midrange with a JBL 104h-2 midrange (often on Ebay) with no other crossover changes does a lot for this speaker.

09-16-2012, 08:02 AM
Have a look at my L100 restoration and upgrade thread here. (

I built some crossovers designed by Dennis Murphy, and also re-built the original crossovers (2 caps, 2 L-pads, not much to rebuild) and devised some switches so I could alternate between them. The upgraded crossovers do much to improve the sound of these speakers, making them sound less aggressive, but still packing a punch. You don't have to spend a fortune on exotic caps, unless you really want to, just use some decent bi-polar electrolytics. I can't tell you exactly how much all the parts cost, but I'm pretty certain it wasn't over $100.