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JBL L100 crossover kit--Murphy or Troels Gravensens

Ridgeback

Ridgeback

New Member
Greetings from a new member. I've been reading and learning a lot here and hope I can refine a topic covered here before regarding crossover kits for the L100.

Many years ago I refurbished a pair of JBL L100's. The thick walnut veneer really took the sanding needed to get out the scratches and the Danish Oil gave it a beautiful patina. New tweeter surrounds, a pair of the orange replacement grills and some better posts really brought these speakers back to their 70's glory from a visual standpoint. They have been serving well mainly as the L-R for my 5.1 AV system.

Then a couple months ago (probably inspired by watching HBO's "Vinyl") I decided to make a modest move toward high(er) fidelity so I invested in a Music Hall 5.3 SE table and a Rogue Audio Sphinx amp. They are truly a massive upgrade from the low-end components I was barely able to afford as a kid in the late 70's. But (I'm sure you can predict where this might be going) the Sphinx brought out some shortcomings in the JBLs--the pronounced mids/upper frequencies. I like the basic sound of this setup but I'm hoping modern crossovers can help refine it. I have invested a lot of elbow grease in the JBLs so I'd really like to take them as far as I can from a listening point of view as well.

I see that there are 2 prominent crossover upgrade paths with regards to kits. The DIY "Murphy" crossover and the Troels Gravesens crossover. Does anyone here have experiences they would care to share with either path? Cost-wise the Murphy path is cheaper but you have to gather your own components based on a parts list / wiring diagram. The Troels path has 4 "quality levels" of pre-gathered kits ranging price from $200-$500. In either case you must assemble the crossovers from the parts based on schematics / diagrams / photos / etc.

As a background, I have pretty good experience putting electronics together. I've successfully built two tube-based guitar amps and many effects pedal clones. Having said that, I can't read a schematic. I have to go by a wiring diagram.

With that in mind, from a listening standpoint, how do the Murphy and Troels crossovers compare? From an assembly standpoint, can I get by with the less expensive Murphy route? Are the diagrams and parts lists clear enough or would I be better off paying more for one of the Troels kits with the reassurance of pre-gathered parts and clear directions? On that note, between the 4 quality levels of Troels kit, is there one that is a clear winner in terms of "value"? I'm guessing that the cheapest $200 one is probably not the one to go for nor is the most expensive $500 with the wax foil coils. Or is it???

http://www.troelsgravesen.dk/JBL_L100.htm

Finally, do these new crossover kits incorporate the existing L-pads or do they bypass them? My L-pads are pretty scratchy and the pots need to be cleaned and perhaps replaced.

Thanks,
Scott
 
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Hope someone chimes in here... I've got the Gravesen kit for his L26 (Morphed to a 3-way) but I haven't put it together. I think people regard Gravesen pretty highly. Hope someone will be able to lend their experience/opinion.
 
Hi Ridgeback

I'm the guy who originally worked with Dennis Murphy to fix the sound on my L100a speakers. I posted about them on Audioholics and the Lansing Heritage forum, and much later here at AK. It seems like you've already read about them at one of those sites:

https://forums.audioholics.com/forums/threads/the-vintage-jbl-west-coast-sound-becomes-the….25014/
http://www.audioheritage.org/vbulletin/showthread.php?13105-New-crossover-design-for-L-100A

I can email you a pdf file with all the schematic diagrams, frequency response curves, parts list, etc. Send me an email address by PM. The last time I looked (Nov. 2013), parts for a pair of the Dennis Murphy crossovers cost $174.30 at Madisound. (Maybe I'll check those prices again.) If I recall, the Gravesen kit cost at least $100 more. I've never heard it, but I can enthusiastically endorse Dennis Murphy's design. I previously posted here on AK before & after frequency response curves, the schematic, and a summary of impressions from owners who did build this crossover:
http://audiokarma.org/forums/index....ration-and-upgrade.349002/page-3#post-9126609

Over the years, I have done that rebuild on three different occasions, once for myself, and two other times to help others.

To answer your questions:
When I rebuilt mine, those L-pads were a problem for me too. Dennis Murphy advised I forget them as they all oxidize over time, even new replacements. So I simply bypassed the old crossover and L-pads and left them in place. In my opinion, the new crossover balances the output of the midrange and tweeter so that no L-pad adjustment is needed.

"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 agreed 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."​

One guy named Leesonic, built his with switches so he could go back and forth between the original and new crossovers. He later admitted he no longer used the old crossover, as the new one was so much better sounding. Still, his work with the switches and their wiring was admirable, and he included excellent photos of it all.

In case you are not familiar with Dennis Murphy, he is an accomplished self-taught DIY speaker designer with an excellent reputation among DIY builders. He also is well known for his role as designer of the commercially available Ellis 1801 speaker, nearly all the speakers sold by Salk Signature Sound. He also now operates his own small internet speaker business, Philharmonic Audio. It's a one-man operation.

From what you described of your own electronic building experience, you had more than I had when I began that project. I believe a wiring layout & diagram is included in my pdf file. If it isn't, I'll add it in.

If you have any questions, I'll be glad to answer them.

Richard
 
I would do the Murphy's, for the reasons Richard gives above. I'm not sure that the Gravesen crossover kits are still on the market, although this page suggests that they may be:

http://www.troelsgravesen.dk/JBL_L100.htm

If they are, I'm sure you'd be happy with them, as well, but for the same grade of parts they will likely cost more than Murphy's, as they have more components. And you can't DIY them, since he has not published the component values. If you do get them, I would not pay for all his upgraded caps, coils, etc.; that seems like overkill to me. I would get the base kit he sells.
 
Thank you litefootdan, Richard and Zonker2 for your replies! Excellent information. I'm glad to hear that the l-pads are bypassed thereby eliminating the problem long-term.

Richard I will PM you for more information. I very much appreciate the benefit of your experience on this.
Thanks!
Scott
 
Hey Ridgeback-
If you do take on the project please do some documentation. Even if it is just some before/after pictures. It is so interesting to see how great some people's work is. Many of the projects here are quite inspirational. I wish I had taken before and after pictures of even simple cap switching stuff. I just don't seem to have the organizational skills needed to document something without is looking like grunge in a scattered garage.... Any way, I hope the best for you and the L100's!!!
 
I think the Murphy crossover is a worthwhile improvement on these speakers. You don't even have to go crazy expensive with the caps, just use the yellow film caps from Erse Audio for signal path caps, and their equally good electrolytics for shunt caps.

Lee.
 
leesonic, I don't see any way to contact you directly. I'm looking for someone that can repair my NAD 7175PE and didn't know if you would be interested, or knew of anyone that would (that will do a good job).
 
Hey everyone,

I've communicated via email with Richard and the folks at Jantzen. Richard very kindly priced out the DYI Murphy kit in today's pricing. Thank you Richard!!!

It turns out the base Jantzen kit and the Murphy kit are both $183 (plus shipping). However, Jantzen also includes HQ inter cable, HQ replacement damping material and the hardboard substrate. That with the convenience factor of Jantzen gathering the parts as opposed to me attempting that and potentially making a mistake/forgetting something pushes me in the direction of the Gravensen kit. I *might opt to bump up one price grade to get the next better caps for the midrange and tweeter section as those appear to be the more "problem" areas of the sound. But no need to go crazy on the wax foil inductors and and "super grade" z-caps and resistors throughout.

I'll try to document my experience and post when complete.

It's so interesting, having read all I could online, about how passionate people have been and still are about the L100. From people who HATE the sound and think it's garbage to the other extreme of people who LOVE the sound--so much so that it's sacrilege to touch a single thing on the design. My impression is that JBL got it close with the high-quality (albeit undersized) cab and excellent drivers but without the obvious advantage of modern driver measuring technology to make an accurate crossover. I'm hoping my impression is correct and the new crossover takes the L100 from really good to amazing.
 
That's a great discovery and a sound decision. Another nice thing about the Janzten kit are all the lovely photos, and the layout diagram, that will help you place and connect the crossover bits on the boards. If you emulate the photos online you will have some gorgeous crossovers, albeit sadly hidden away in use.

JBL-L100_XO-layout_Superior-Z-e_edited-1.gif


JBL-L100_KIT_2_xover-B.jpg
 
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Hi Richard. I could not find any reference to a direct PM for you, so I hope you can send the PDF as well as parts list to me at
b t m o t o 1 at g m a i l dot c o m. Thanks much
 
Any update on this project?

Edit.... I should search more lol found a dfollow up thread.... disregard... carry on
 
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So. I drooled at the idea of the TG crossover for several months but I was put off by the price (more than I paid for my L100's). Then I realized, if I wanted a much better, much more accurate speaker w a highly improved tweeter I should just buy that speaker. (then I got a set of l100t3's or a pair of bone stock horizons). I know everyone craps on the l100 midrange jump and you could keep going from there, but there isnt a much more enjoyable speaker to listen to brash electric guitar-rock music. I'd say keep the l100's stock (unless you physically can't fit another speaker in your apartment/house or just love tinkering) and get any number of more modern, more accurate speakers if that's what you feel like you need. It's a legend for a reason.
 
R Swerdlow said:
Here is a PDF file of the Dennis Murphy crossover for the JBL L100a, with all the schematic diagrams, frequency response curves, parts list (as of Dec. 2017), etc.
Click to expand...
Richard
This information is terrific. Always loved my JBL L100a's except for the "shrill" female vocals on high notes and the "s" sound in vocals. Is that what you all mean
when you refer to "bright" or "forward"? I used to love these for rock but now I'm pretty pleased with their orchestral sound. I'm meaning to use your Murphy diagram and parts list
to change the crossovers in any case as all other cosmetic work needed I've completed.
Thanks for the completeness of your update.
Al
 
Al Japely said:
Richard
This information is terrific. Always loved my JBL L100a's except for the "shrill" female vocals on high notes and the "s" sound in vocals. Is that what you all mean when you refer to "bright" or "forward"?
Click to expand...
Yes, that's what I meant. There are some musical notes that can excite a harmonic overtone in the 6 to 7 kHz range, where the JBL mid-range driver has an unnatural sounding peak. When that happens, it's an ugly sounding noise, worse than shrill. The redesigned crossover eliminates that.
Al Japely said:
I used to love these for rock but now I'm pretty pleased with their orchestral sound. I'm meaning to use your Murphy diagram and parts list to change the crossovers in any case as all other cosmetic work needed I've completed.
Thanks for the completeness of your update.
Al
Click to expand...
Thanks for the kind comments. Good luck with the project.
 
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