Re-Capping the L100

[Wagner]

Hello to all,
I own a "minty" pair of late model L100As. I acquired them from the original owner at a price so low I could not pass them up.
I am well aware (painfully so) that this particular JBL is the topic of much "debate".
Initially, they were going to do primary duty as "shelf queens" as I feel it is good to own a pair of these if for no other purpose than to round out one's collection of all things JBL. That position gradually changed (maybe as I have gradually but consistently been losing my hearing!)
Old age is a bitch!
I happen to enjoy mine, primarily as they are the one speaker I happen to own that does speech intelligibility extremely well and that is a VERY important attribute for me.
I use them a lot and with a good tube amp I enjoy them musically also, especially when playing vinyl.
My main complaint though is that they are almost dull sounding on top at times; the tweeter's output is almost nonexistent, even with the L-pad cranked wide open. Not rolled off, just not there. I have tested the tweeters and they are fine, as well as L-pad cleaning. Their output is just EXTREMELY attenuated, no matter the amp or source material. The notorious "mid" picks up a lot of the slack but still, something is amiss, as in "missing in action".

So, I am considering a re-cap. I have some reservations though as this will require the painstaking removal of the foilcal in order to not damage, or worse, destroy it. I can manage the job but am only interested if I have enough subjective evidence to feel reasonably comfortable that it will be worth the effort. My L100s have the old style brown paper tube type caps which I have had go south on other systems.

What I would appreciate very much is that if any members here have actually re-capped their L100s to please share what the results were.

I also am finding it odd that very few, if any vendors, offer a 8uF metabolized polypropylene type (in a realistically priced cap)? Madisound does have one in Solens, but then again the tolerance is 5%, so, so much for that. The common value nowadays seems to be 8.2uF and I can source those in the 1% Daytons from PartsExpress. I have had good luck with the Daytons in the past and will use a JBL style .01uF foil bypass.

I remember Zilch once endorsing the Solen + an Audicap PPT Theta for the bypass with a big "thumbs up". Don't know if he was speaking as much to the caps themselves or to the results of re-capping and bypassing tired old L100s.

Either way (and hopefully avoiding a digression into a cap brand debate) would those of you who have re-capped your L100s please share your experiences and results with me? And does anyone feel that the additional .2uF in so simple a network would have any negative impact?

Thank you so very much for your time and consideration!
Thomas

[Swerd]

Hi Wagner. Saw your question about L100As and think you might benefit from reading this old but relevant thread

http://www.audioheritage.org/vbullet...ign-for-L-100A

I think the problem you described, the tweeter sound dropping out, could easily be due to oxidation of the old variable L pads. This is a common problem. Spray some contact cleaner, like Caig Deoxit, into the L-pad, and turn it all the up and down repeatedly. If that makes the tweeter sound come back, even temporarily, the L-pad is your problem. Clean or replace them. Better yet, build an entirely new crossover as in the link.

As far as tolerances for crossover capacitors, anything within ±10% of the printed cap value works. Using a cap with 8.2 µF instead of 8 µF will work without problems.

[Wagner]

Hi Wagner. Saw your question about L100As and think you might benefit from reading this old but relevant thread

http://www.audioheritage.org/vbullet...ign-for-L-100A

I think the problem you described, the tweeter sound dropping out, could easily be due to oxidation of the old variable L pads. This is a common problem. Spray some contact cleaner, like Caig Deoxit, into the L-pad, and turn it all the up and down repeatedly. If that makes the tweeter sound come back, even temporarily, the L-pad is your problem. Clean or replace them. Better yet, build an entirely new crossover as in the link.

As far as tolerances for crossover capacitors, anything within ±10% of the printed cap value works. Using a cap with 8.2 µF instead of 8 µF will work without problems.

Good Morning!
Thank you for your reply and for the suggested reading. Although it has been some time, I remember that thread from way back; it pre-dates my acquisition of L100s, so it will do me good to take another look. I am also very interested in re-visiting some of the "Zilch plugs" discussions.
I am aware of the all too common L-pad aggravations. I am satisfied that I have eliminated that from my equation at least. Drowning them in DeOxit was the first order of business the day I received them. They measure well and have no dead spots. Still, I take your words into consideration and plan to drown them again if I do the re-cap when they will be a Hell of a lot easier to access!
I am not suffering any dropouts or dead spots (or noise for that matter). The tweeter produces sound throughout the usable range of the pot; it is just very attenuated as I have already mentioned. I have owned several other pairs of JBL from this period (paper cone tweeters) and have never had any of them with such an anemic H.F. output. The other models employed the 3-position H.F. adjustment switch however.
I plan to leave this pair as built, only to refresh the capacitors if I can gather up the steam (steady hands) to do so.
That is why I am essentially interested in hearing the results others have realized by doing the same simple "one for one" swap out.
I have looked at, and for about 2 seconds contemplated, the Troels Gravesen mods. Maybe if I come across another pair someday, but these I am going to leave as built. Changing THAT much of a system, to my mind, makes them another speaker. Call me sentimental (or deaf) but I would like to just hang onto a "stock" pair of L100s, for better or for worse! I enjoy them very much "as is" but for this shyness in the H.F.
I do not wish to appear as if I am arguing with your suggestion, I am not. I just do not feel as if it applies to my particular complaint. And again, my only reluctance to just going ahead and trying some fresh caps is the tedious nature of the job of simply getting to them, unless I was willing to take the hatchet approach! The last thing I want to do is to damage or destroy my perfect foilcals which have made it 4 decades plus without a mark!
I really would love to hear what others' results were with a straight across cap swap.

Thank you again,
Thomas

[Swerd]

There is little to go wrong with a tweeter in the L-100A:

With a failed tweeter, there should be no sound at all.

If you've already tried DeOxit, you've eliminated the L-pad as a problem.

Usually, if the tweeter cap has failed, the tweeter should get no signal at all.


The only thing I can think of is that in the L-100A, the midrange driver has no high frequency cut-off at all. As a result, it can be difficult to tell if the tweeter is working or not, especially if your high frequency hearing is not as good as it was. You can easily try using new caps, and L-pads, without touching the existing crossover board. Remove the woofer, disconnect its 2 wires (noting which wire connected to which terminal) and you'll see how to bypass the existing board with a new one that you built.

[SEAWOLF97]

The pots are first suspect, but you've been there already.

Next, I'd pull the tweets (unless they are those le-20's with the beauty ring) or work from behind and unplug and clean up the leads.. maybe contact surface corrosion ?

[Wagner]

There is little to go wrong with a tweeter in the L-100A:

With a failed tweeter, there should be no sound at all.

If you've already tried DeOxit, you've eliminated the L-pad as a problem.

Usually, if the tweeter cap has failed, the tweeter should get no signal at all.


The only thing I can think of is that in the L-100A, the midrange driver has no high frequency cut-off at all. As a result, it can be difficult to tell if the tweeter is working or not, especially if your high frequency hearing is not as good as it was. You can easily try using new caps, and L-pads, without touching the existing crossover board. Remove the woofer, disconnect its 2 wires (noting which wire connected to which terminal) and you'll see how to bypass the existing board with a new one that you built.

I know I am not suffering a hard failure. I have had those old brown cardboard and wax caps do strange things in the past (with other systems) short of hard failures. That is one of the experiences that lead to my inquiry here.
I don't think you are following me here; the tweeter is working. I just don't think it's working as well as it should. It's not as easy for me to order up new parts and construct a new network as an experiment as it is to solicit those who have re-capped their L100s to share their experiences and results. Subjective and anecdotal as that may be. May as well start in on removing those foilcals!

Just looking for a little feedback from those who have actually done theirs.

Thanks again,
Thomas

[Wagner]

The pots are first suspect, but you've been there already.

Next, I'd pull the tweets (unless they are those le-20's with the beauty ring) or work from behind and unplug and clean up the leads.. maybe contact surface corrosion ?

Hello,
I did when I cleaned up the boxes. The tweeters were removed to facilitate the installation of the new foam diffusers.
All drivers actually. I clean and treat all connections in 40 years old speakers.
All connections have been well cleaned and treated. I also installed new 5-ways in this pair and soldered the leads for the woofers to the new terminals.
Everything is clean and tight.

Thomas

[Greg86z28]

Just an FYI, but on my L150s, one of the tweeters "didn't work". I tried deOxit on the L-pads and it didn't help. I ended up finding that the actual L-pad it's self had lost contact on the inside (some of the metal contacts had been bent apart and no longer were in contact). I took it apart and did some rebending of the contacts (to make sure they were always in contact) and woo-la, fixed.

[grumpy]

swap tweeters.

[Greg86z28]

swap tweeters.

^^ Good idea. Easy and quick to find out what's going on.

[Wagner]

The complaint is with both boxes.
Now I am getting into more detail than I wanted; I have looked at output with an SPL meter and my ears using a toilet paper tube while running some pink noise.

The tweeters are WORKING! Both tweeter's voice coils measure out at about 3.8 ohms DCR if I remember correctly (it's been a couple of years) They are just down in subjective level and down as compared to everything else I have ever owned that used LE25s.

All I would love to hear is what the results were for those members that actually re-capped their L100s with a "1 for 1" approach.

Please

Thank you,
Thomas

[Doctor_Electron]

HELLO. i THOUGHT I WOULD TOSS IN ANOTHER POSSIBILITY
( HOPEFULLY NOT THE CASE ). IF THE DRIVERS ARE THE ALNICO TYPE, IT IS POSSIBLE THAT THEIR FIELD STRENGTH HAS DIMINISHED FOR WHATER REASON (s). nATURAL AGING, SEVERE SHOCK AND/OR HEAT DAMAGE CAN BE COMMON CAUSES.

I DID A STINT APPRENTICING AT AN AUTHORIZED JBL PRO SERVICE SHOP, AND ONCE IN A BLUE MOON OR TWO WE WOULD SEE THAT, BUT MOST OFTEN OCCURING IN CHEAPER BRANDS WITH A LOT LESS GAUSS TO BEGIN WITH, AS COMPARED TO THE MUCH BEEFIER JBL DESIGNS.

IF YOU DOWNLOAD THE SERVICE SHEET FOR YOUR MODELS, YOU WILL FIND A TEST PROCEDURE AS PART OF THE DATA.

WE HAD NO SUPER SOPHISTICATED TEST GEAR FOR THE OUTUT LEVEL TEST, BUT SIMPLY SETTIG UP A REFERENCE MARK USING DECENT MIC AND VTVM / VOM ETC. ON THE AMP OUTPUT WHILE MEASURING THE SPL OF A KNOWN GOOD DRIVER. THEN TEST THE SUSPECT UNIT, LEVELS SHOULD MATCH CLOSELY.

I STILL HAVE A NIFTY PAPERWEIGHT, A 2402 WITH SO LITTLE OUTPUT THAT TO HEAR ANYTHING AT ALL FROM IT REQUIRES PUTTING MY EAR RIGHT IN THE THROAT.

I WOULD NOT TRY THAT WITH AN IN-SPEC "BULLET".

SAY, WHAT WAS THAT YOU SAID? HUH?

GOOD LUCK, I HOPE THE PROBLEM IS LESS SERIOUS, BUT COULD BE OVERLOOKED SINCE IT IS A ~SOMEWHAT~ RARE HAPPENING.

"dE"

[Wagner]

HELLO. i THOUGHT I WOULD TOSS IN ANOTHER POSSIBILITY
( HOPEFULLY NOT THE CASE ). IF THE DRIVERS ARE THE ALNICO TYPE, IT IS POSSIBLE THAT THEIR FIELD STRENGTH HAS DIMINISHED FOR WHATER REASON (s). nATURAL AGING, SEVERE SHOCK AND/OR HEAT DAMAGE CAN BE COMMON CAUSES.

I DID A STINT APPRENTICING AT AN AUTHORIZED JBL PRO SERVICE SHOP, AND ONCE IN A BLUE MOON OR TWO WE WOULD SEE THAT, BUT MOST OFTEN OCCURING IN CHEAPER BRANDS WITH A LOT LESS GAUSS TO BEGIN WITH, AS COMPARED TO THE MUCH BEEFIER JBL DESIGNS.

IF YOU DOWNLOAD THE SERVICE SHEET FOR YOUR MODELS, YOU WILL FIND A TEST PROCEDURE AS PART OF THE DATA.

WE HAD NO SUPER SOPHISTICATED TEST GEAR FOR THE OUTUT LEVEL TEST, BUT SIMPLY SETTIG UP A REFERENCE MARK USING DECENT MIC AND VTVM / VOM ETC. ON THE AMP OUTPUT WHILE MEASURING THE SPL OF A KNOWN GOOD DRIVER. THEN TEST THE SUSPECT UNIT, LEVELS SHOULD MATCH CLOSELY.

I STILL HAVE A NIFTY PAPERWEIGHT, A 2402 WITH SO LITTLE OUTPUT THAT TO HEAR ANYTHING AT ALL FROM IT REQUIRES PUTTING MY EAR RIGHT IN THE THROAT.

I WOULD NOT TRY THAT WITH AN IN-SPEC "BULLET".

SAY, WHAT WAS THAT YOU SAID? HUH?

GOOD LUCK, I HOPE THE PROBLEM IS LESS SERIOUS, BUT COULD BE OVERLOOKED SINCE IT IS A ~SOMEWHAT~ RARE HAPPENING.

"dE"

The LE25 utilizes a ceramic magnet.
Thomas