JBL L100 restoration and upgrade

Nice work. Could you give us some sort of detailed review? And primarily whether you prefer the JBL sound or the Murphy sound? Or are they just different?
Thanks

Jon
 
I recently stumbled over Lee's thread about his nice work with his L-100s. I had replaced the crossover in my old L-100s in 2006 and wrote all about it here http://forums.audioholics.com/forums/threads/the-vintage-jbl-west-coast-sound-becomes-the….25014/. Lee took it to the next step by the complex wiring that allows him to switch back and forth between the old minimal crossover and the new flat one.

To answer some questions that were asked in this thread, the L-100s with the original crossover measured like this:
old-on-axis-response-gif.3476


The same speaker with the new crossover measured like this:
new-on-axis-response-gif.3474


And here is the schematic for the new crossover without Lee's added switches:
new-crossover-jpg.3477
 
Nice work. Could you give us some sort of detailed review? And primarily whether you prefer the JBL sound or the Murphy sound? Or are they just different?
If you go to the original Audioholics thread http://forums.audioholics.com/forums/threads/the-vintage-jbl-west-coast-sound-becomes-the….25014/ you can read several listener's impressions. All of them greatly prefer the new revised crossover over the original.

My own as Swerd (post #16)
How do they sound? In a word, excellent! My very first impression when I built the first one, was that the new crossover made the speakers a lot less sensitive. I had expected that, but it was still quite noticeable. But despite that, the new crossover did not suck the life out of those JBLs. (In fact the new crossovers make the speakers about 1 dB less sensitive at 500 Hz and about 3 dB less sensitive at 1000 Hz.)

I spent about a week listening to one speaker with the new crossover, comparing it to the other speaker with the old crossover. After adjusting for the change in volume, the new crossover was a clear winner. Both me and my wife agree that the new crossover sounds much better. I tried a wide variety of music that I knew well, including some music where I actually liked the effect that the bright JBL upper-midrange had. The new crossovers eliminate the glare and brightness that I thought I had gotten used to. I remembered that years ago, I used to play with the bass and treble controls, and fiddle with the variable L-pads on the speakers to adjust midrange and tweeter levels, trying without success to control that ear-fatigue-inducing brightness. The new crossover does it much better. It really amazes me how much better speakers sound when the frequency response curve is flat.

Bwilkinson (post #71)
Words cannot describe the difference in sound between before and after. When I was waiting to get these JBLs, I had high expectations. I first listened to them, and to say I was not impressed was an understatement. With this crossover, they are everything I want them to be - including the 70Hz bump. It is exactly where I boost sound typically (personal taste). The top end is smoothed right out, the vocal separation is more than impressive. I can hear each individual voice placed in the mix. The location of the instruments is incredible.

I am going to have a whole lot of fun with these speakers. Thank you for all your help, and although Dennis Murphy has no clue who I am, please thank him for the crossover design.

Leesonic same as the OP in this thread (post #90)
What I can tell you is the difference between the Murphy crossover and the JBL is staggering. With the JBL, it sounds like the midrange is the tweeter as well, there is FAR too much treble getting to it. I've just posted a request on a Freecycle web site I'm on for a microphone. If I can get hold of one, I'll post a video up on YouTube of the differences between the two crossovers.

CAJBL (post #123)
Overall, following the schematics building the crossover was very straightforward. What I didn’t expect was how much better these speakers actually sound. I know there is still a little bump in the mid bass but I tend to like that. I eventually plan on building a new enclosure for a more purist set of monitors, but until then I am loving these speakers.

Tested them with Steely Dan Aja, Roger Waters Amused to Death, and an ELP compilation and I am floored by the difference. On the title track of Amused to Death I can actually listen at concert level and instead of my ears bleeding I am able to hear detail that had been lost in the chaos of the original speakers. If I get tired of the mid bass I might try plugging the port, but I don't foresee that happening. I have a set of 4411's to compare to and the only noticeable difference is in the high frequency response, but I may try an 035ti to see if that yields an improvement over the LE25-2. So in conclusion, I am impressed. This crossover brings the L100 to a different level.

And finally, here is a photo of the crossover I built, before soldering it with all the connecting wires

attachment.php
 
Uploaded pictures to repair broken picture links, caused when Comcast pulled the plug on personal web space.
 
WOW! I can't believe I missed this thread! Excellent work and detailed pics!
Very nice.
 
What's weird is the midrange interaction with the woofer. I don't know what you call it, but we all know the sound a pair of out-of-phase speakers make. That weird sound like it's coming from behind you, or inside your head, it's kind of hard to describe. I've been to peoples houses (who should know better) and told them one of their speakers is wired back to front.

Hi, I own a pair of L100, and have the same feeling of you! the sound (great sound) sometimes seems to came from behind, like out-of-phase.

What if i try to invert the midrange's wires? Could I cause serious issue? I honestly don't think so, but I would like to hear your opinion.

Thank you and congratulations for your great work!
 
Hi, I own a pair of L100, and have the same feeling of you! the sound (great sound) sometimes seems to came from behind, like out-of-phase.

What if i try to invert the midrange's wires? Could I cause serious issue? I honestly don't think so, but I would like to hear your opinion.
I'm not Leesonic, but I was involved with the redesign of the L-100 crossover that Dennis Murphy did. The work was done with my speakers, and I wrote the original description of the new crossovers: https://forums.audioholics.com/forums/threads/the-vintage-jbl-west-coast-sound-becomes-the….25014/.

With the original JBL crossover, the midrange driver was meant to wired in opposite polarity to the woofer and tweeter. With the phase delay of those 1st order crossovers, this was necessary. If you keep the original JBL crossover, but reverse the midrange driver's wires, it will be out of phase with the woofer and tweeter. It won't cause any damage, but it will stomp on the sound quality.

In the Murphy crossover, the acoustic phase delay of the crossover circuits are the same for all three drivers. They will all be in phase with each other. As a result, they should all be wired with the same polarity.
 
In the original XO, the tweeter and the mid both had just a single cap on them, making both a 6db per octave slope. How is the mid the only driver out of phase with the woofer?
 
In the original XO, the tweeter and the mid both had just a single cap on them, making both a 6db per octave slope. How is the mid the only driver out of phase with the woofer?
JBL's schematic of the L-100A showed the mid driver with opposite polarity to the woofer and tweeter. Those wiring polarities were probably based on their acoustic performance as judged by listening, trial and error style. As you said, these 'crossovers' had only high-pass filters without any low pass filters at all. A single cap does introduce some phase delay. But it doesn't resemble what we see now where there are high-pass and low-pass filters to cover all driver hand offs.

I wasn't present when JBL designed those crossovers, so I can only guess :).
 
I should get these out of the closet and play them again. My daughter is now approaching 8 years old, and knows to leave the speakers alone, so I can run them without grills.

Lee.
 
JBL's schematic of the L-100A showed the mid driver with opposite polarity to the woofer and tweeter. Those wiring polarities were probably based on their acoustic performance as judged by listening, trial and error style. As you said, these 'crossovers' had only high-pass filters without any low pass filters at all. A single cap does introduce some phase delay. But it doesn't resemble what we see now where there are high-pass and low-pass filters to cover all driver hand offs.

I wasn't present when JBL designed those crossovers, so I can only guess :).

Thanks for the response. I'm going to say that I thought that was wrong, that maybe both the mid and HF drivers should be wired out of phase to the woofer, at least that seems right to me. However, a couple of cross-over design books that I have says that you should do that on 12db per octave slopes, not 6. I realize you were not there, neither was I. It might have been fun to be a mouse in the corner tho.

If I had a pair here, I'd mess with that.....simple enough to do. (and undo).
 
JBL woofers were polarity-reversed compared to the rest of the industry until (IIRC) the 123. If you apply positive to the red on these early woofers the cone will draw in. You will see that the crossover wiring reflects this, and beginning around 4312A the new woofer (wiring, marking, whatever) is wired red positive, applying positive to red on these later to current woofers will cause the cone to protrude out.
 
Hi
Reading this with much interest thank you to all
I know this thread is sort of old though
Can anyone show me the schematic on which the mid is wired in reverse as I can only see examples where it is the woofer that is is often wired backwards due to the voice coil convention
Thank you and thank you for this great resource!
Michael
 
Talking about the crossovers mods with someone here on AK prompted me to get these out of the closet and set them up. It's easy to hear why these were used as monitor speakers, which ever crossover design you use. They are very detailed speakers, I found myself hearing sutble little details in songs that I've known for years.

JBL-L100s-Feb2019-01.jpg

JBL-L100s-Feb2019-02.jpg
 
Listening to a Roy Ayers album yesterday, I heard some backing vocals I don't ever remember hearing before.

I'm listening to "Frampton Comes Alive" right now - Do You Feel Like We Do?
 
I scored a pair for $60 a few years back, but only got around to listening to them recently.

Sure, they have a signature sound, but I don't feel a need to "improve" them.
 
Here are the vertical array L-100A crossovers revealed-
I ended up just replacing the 3uf tweeter cap and left the chokes in place.

Is there a SIMPLE "better" alternative to this original crossover or will a swap to a capacitor change the original voicing?

IMG_8806.jpg IMG_8807 (1).jpg IMG_8808.jpg
 
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