[HMayes]

I have a pair of JBL L-100's. I don't know too much about speakers other than there is a device to split the different frequencies out and send them to the appropriate drivers. Do tweeter drivers go bad? I don't know if it's the tweeter or the wiring or maybe something else. Does anyone have any idea, or any ways I can troubleshoot this? I've noticed you can get quite a few JBL L-100 parts on E-Bay, but I need to figure out what to buy first. Any help would be appreciated. Thanks!

| Hal

[tanchiro58]

Do tweeter drivers go bad? I don't know if it's the tweeter or the wiring or maybe something else.

What do you have now in your JBL L-100? Are they 077 or bullet 075 tweeters? I had a pair of 077 before and they sound pretty warm and musical. These tweeters never go bad except the diaphragm. You should check your crossover or you might add a L-pads. Good luck.

[JoshK]

L-100's are terrible speakers and you should send them to me quickly, so that I can properly dispose of them.  You don't want your audiophile friends to find out you own them, so hurry and send them to me.

[HMayes]

Haha. Thanks for the advice JoshK I'll get right on that. I pulled the tweeter and it just says Model LE25 on the back. How do I check the crossover, and what are L-pads? Thanks.

| Hal

[SET Man]

Hey!

   Those are classic JBL speaker.

  Here is the link about them...

http://www.audioheritage.org/html/profiles/jbl/l100.htm

  FYI... L-pad is like a volume control that you could install in your speaker to tone up and down drivers level... mostly tweeter and mid-range driver. But if the speaker sound good to you now than there is no need to put one in. Cheap L-pads do degrading the sound quality a somewhat... but make speaker more flexible.

   Anyway, if  your are in great condition than enjoy them! 

Take care,
Buddy

[HMayes]

Great article, and believe me, I DO enjoy these speakers. Back to the tweeter problem. Would it be safe to connect the leads from my amp directly to the tweeter (and keep it at a very low volume) just to test if the tweeter even works? If it is the crossover, I'm not sure how to access it. It seems that the only way to get it out of the cabinet is to take the woofer out. I unscrewed the four screws holding the woofer in place and pushed on the back of the housing but it did not want to budge. I didn't force it because I can't really see anything (I am reaching through the hole where the tweeter sits) and I'm not sure how it is constructed. Also one of the screws to holding the crossover in place is underneath the JBL label which I am reluctant to peel off for fear of damaging it. The speakers are in really good shape and I'd like to keep it that way. Any advice?

| Hal

[slbender]

Hi Hal,

Yes tweeters can be blown, but the LE-25 is a pretty capable unit. The pots in the crossover, if they are there can also develop dead spots, so perhaps try them across their range. Also the caps that make up the high-pass section of the crossover can also become less capable over time.  IF it seems like you have no treble out of the L-100's try testing with FM interstation noise between channels or at the lower end of the band.  Or possibly on a phono input with the turntable's RCA plugs pulled out of your preamp/receiver, there should be some across the audio band full range hiss if you crank the gain up.  In a pinch, some consider this hiss a type of "white" noise usable as a built-in test signal... to see if each of the drivers in your L-100's are responding.

Using FM noise, or the phono hiss, you should be able to get a feel for what is a natural sounding "white" noise in your room environment, as the JBL speakers are very efficient, on the order of 92 dB for 1 Watt / 1 Meter.  The L-100, if I recall correctly, uses the same three drivers, as in the 4311's, and the 4311's do have both tweeter and MR control pads, not sure if the L-100 also have those two controls.  While I prefer the MR and TR controls at about 1/3rd up, full up would be more midrange and treble, sort of the "West Coast" sound.  Of course, it could be your hearing which may be blocked by wax buildup or exposure to intense noise, the human ear is delicate and only a transformer at the level of the outer, middle, and inner ear, and subject to damage and destruction from intense noise, prolonged exposure to rather loud sounds, or from disease, or other sources of damage. YMMV.


-Steven L. Bender, Designer of Vintage Audio Equipment

I have a pair of JBL L-100's. I don't know too much about speakers other than there is a device to split the different frequencies out and send them to the appropriate drivers. Do tweeter drivers go bad? I don't know if it's the tweeter or the wiring or maybe something else. Does anyone have any idea, or any ways I can troubleshoot this? I've noticed you can get quite a few JBL L-100 parts on E-Bay, but I need to figure out what to buy first. Any help would be appreciated. Thanks!

| Hal

[HMayes]

Thanks for the post sbender. I failed to mention in my first post, one speaker appears to be performing flawlessly while the other has no high range and I am now wondering about the mid-also. (I'm no audiophile so I'm not quite sure which ranges should be coming through the woofer vs the midrange driver, all I know is that one speaker sounds wrong). I don't think my speakers have treble or mid control pads, I do have brilliance and presence settings though. I'm not entirely sure what those do though.

EDIT: I think i found the problem. When adjusting the brilliance and presence dials I was able to get both the mid range tweeter and high range tweeter to work. Is there any way to service the crossovers or is it cheaper to just replace them? Thanks again.

| Hal

[macrojack]

Brilliance is tweeter and Presence is mid-range. If you were able to get everything working by moving those controls, you should work them more and if you can get some contact cleaner in there, that would help. The contacts must have corroded a little over time. Those speakers are likely more than 30 years old now.
I have a pair of L-200 from the same era. Hardly the last word in resolution but they will rock with the best.

[tanchiro58]

you should work them more and if you can get some contact cleaner in there, that would help. The contacts must have corroded a little over time.

o

That is absolutely correct. I bought a pair of Jensen RP302A super tweeters and they sound horribly harsh and dry. After replacing the new wires they sound more warmer and sweeter.

[HMayes]

Wow. That is great news. I believe my dad purchased the speakers in 1974, so I wouldn't be surprised if there were some rusted parts in there. I'll definitely try the contact cleaner and keep you posted.

| Hal

[macrojack]

Nothing so bad as rust, Hal. Just a little corrosive film. The first thing to go on those speakers is usually the foam waffle pattern grills.
Your contacts just need to be rotated vigorously a few times. That should be enough to rough them up and re-establish good electrical contact. If it is possible to spray a tiny amount of contact cleaner into the pots, so much the better but I wouldn't worry too much about that if they are working O.K. now.

[Wayner]

I had a pair of L100's. If I remember right, there was a dual capacitor that did a simple 12db roll off for the midrange and tweeter (different values for each driver). I also recall a plug and a outlet where the circuit was connected. I suggest taking out the woofer and have a look-see. If both midrange and tweeter are out, I would suspect a connection point in the cross-over. The woofer is rolled off naturally (which makes them great candidates for bi-wiring).

The midrange and tweeter are built extremely robust so unless someone sent gobbs of DC into them they should be OK. To check the midrange, put a 1.5 volt battery across the terminals for an instant and listen for a click. Do the same for the tweeter. If you have no sound the drivers may be bad.

Do not connect the tweeter directly to the amp. You will send full frequency to it and then you will have a blown tweeter.

 

P.s. I would wire out the L-pads or replace them as they may be past the point of sprays helping (they are 30+ years old).

[WOR Radio]

Actually it is an 8mf and a 3mf cap, 8 for mid, 3 for tweeter and it is a 6dB/oct slope.

All drivers are allowed to go "as high as they will" as the L100 contained "no" inductance coils in the x/o.

The two caps serve as HPF's and two L pads for balancing the "presence" (mids) and "brilliance" (tweeters)

There, you have the entire x/o schematic.