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JBL L100 Crossover Project Invite

Lou F Quincy

Lou F Quincy

Super Member
Greetings, Welcome to my class where YOU are my teachers.
I am in the beginning stages of redesigning the crossover network on an old pair of JBL L100 Century speakers and I'd like some feedback and input on the component choices. I generally just use the Parts Express catalog (yes, I'm a hopeless boomer) for choosing capacitors and inductors but I decided to use a free web program called XSim that helps make choices and gives theoretical results (though I haven't quite figured it all out yet).
Anyway, the schematic below is my first draft. No parts ordered yet.
I'm more of a dabbler/tinkerer than a specialist but I'm not too old to learn some things and activate some unused neural pathways. Doc says it's good for me to think outside of the .... "SQUIRREL !!!"

XSim JBL L100 Crossover Mod.jpg


Btw, I've read the Murphy, Janzen, etc crossover examples, and I'm sure they're excellent examples but I'm looking to design something simpler and enjoy the process. (Though, admittedly I'm nosing into intellectual property.)

Thank you.
 
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Which version of the L100? I believe that the L100 and L100A have negative woofers where the L100A (late) has a positive woofer.

Perhaps post which drivers you're working with?
 
On the L Pad face is Serial # 188xxxA
It has the non aligned tweeter and mid.
So it should be the L100A.
Tweeter LE25
Mid LE5-2
Woofer 123A-1

Is there a FRD for those drivers?
 
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I don't know the answer, but I applaud your goal; the Gravesen and Murphy designs are a bit too expensive, complex and power-hungry for my tastes. I've often thought that later crossovers like the L36 and L50 might serve as a good starting point. The Gravesen site has a lot of details on the drivers, as you've seen. The midrange has a peak around 8K that should be avoided with a lower crossover point, as later JBLs did.
 
123A-1 is the L100A early version, still a negative woofer design. In your schematic above you will want to reverse the polarity on the 123A-1 woofer using red for negative.
 
Thanks. Yea, going by the tech manuals retrieved from Hifiengine, things get a little muddled. I'll do a 9 volt battery check eventually to confirm polarity.
I'm even considering laying out the crossover inside an exposed and openable box that I can easily access electronics to modify. Sort of a test lab speaker setup. Heretical?
II don't like unscrewing speakers too much as the wood starts to suffer. Besides, I know myself enough to know that I'll want to monkey with it after I get it all back together.
 
There is no law that says XOs have to be on the inside. You might want to put them on the outside (perhaps permanently), as I can bet there will be some more changes before its done. One complaint of mine with my L100s was the fact that the midrange was allowed to run out on its high end. That means the tweeter and the midrange were both producing the same frequencies for some band width, and I think that is not a good thing.
 
I was shocked when I discovered how simple of a crossover these JBL's have. No inductor on woofer. No inductor for mid. Just a cap for mid and a cap for tweeter with the Lpads for each. Screams "White Van".
I've had them for a few years and have enjoyed them but their brightness is fatiguing and I've got chronic tinnitus so I have to tame them down. I don't push them very hard as they are in a narrow room environment with encroaching sloping ceilings but I know they can sound better.
They are powered by a wonderful NIKKO ALPHA III mosfet amp with 80 watts capability. Also can be augmented with a pair of 12 watt Hoffman mono tube amps through a NIKKO 4 channel preamp into (at this time) Infinity RS525 s.
The Crusaders "Rhapsody In Blue" gives me chills. (Hats off to the late great Bill Withers)
 
The XSim program is quite a convenient tool, btw. The learning curve has given me some micro fits but the more time I invest in it, the funner it gets. Lots of real time graphs.
I found a tutorial at YouTube that helped somewhat. He mainly just buzzes the peaks of what you need to know but it's effectively informative.


Enjoy.
 
If you want it in the lansing forum, click on REPORT in your original post and ask the Moderator to move it.

The upside is more JBL people frequent there, the downside is that your questions are more generic speaker/crossover related and you'll get less of the general experimenters and such from this forum (and I think this forum gets more readers/posters).
 
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Just throwing this up for closure. This is the "as built", Very satisfied with results.

At higher volumes the original is too shimmery and piercing, The midrange is uncontrolled and harsh. Still listening in new and old mode (Left vs right). Kind of fun and interesting to adjust low, mid and high passes - to extremes - with an equalizer.

Voicing on upgraded side is clear and full. Drums sound like drums. Crisp and tight with solid and deep bass. Volume hasn't gone past 1/2 with no problems. That's about all my ears can take. All drivers are original stock. I'll push them harder when I get the other side modified.

Also covered through another question...

https://audiokarma.org/forums/index...binations-in-crossovers.949867/#post-14589770

(Sorry if I broke a rule)

Thanks for the help.
 
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Desperately seeking speakers! (Actually I have them; that’s a bad pun).

Just completed the Dennis Murphy crossover for my 1973 vintage JBL L100 Century’s. Not using L Pads; both L & R speakers worked ‘fine’ before new crossover build.

So…..bass side passes sound just fine; midrange and tweeter; zilch. Built per Richard Swerdlow’s specs and schematics; sourced my parts from the same sources (Parts Express and Madison’s).

Where should I begin my search to solve problem? Tested all components for nominal values before assembly; should I tear the midrange and tweeter paths down and start all over with them? I’ve got everything on a pegboard, so tear down, testing again and rebuild is not a huge issue (except time!).

Thanks much in advance -

DJG
 
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