JBL L26 - bad crossover?

[sneakyimp]

I inherited my father's JBL L26 speakers. I had the woofers repaired last year and then played them too long/loud on my birthday and noticed the next day that all the top end was gone.

I purchased some replacement tweeters on Ebay only to realize that the problem appears to be in the crossover.

I'm wondering if this is expensive to fix? Worth it? Can anyone comment?

[Feanor]

I inherited my father's JBL L26 speakers. I had the woofers repaired last year and then played them too long/loud on my birthday and noticed the next day that all the top end was gone.

I purchased some replacement tweeters on Ebay only to realize that the problem appears to be in the crossover.

I'm wondering if this is expensive to fix? Worth it? Can anyone comment?
What makes you suspect it's the crossover that's the problem? Can you hear the tweeters at all? Are you sure they are hooked up properly?

Consider that the crossover values might need to change if the parameters of the new tweeters are different from the old.

However crossover components are relatively cheap, so repair might be a good option.

[cjpremierfour]

I inherited my father's JBL L26 speakers. I had the woofers repaired last year and then played them too long/loud on my birthday and noticed the next day that all the top end was gone.

I purchased some replacement tweeters on Ebay only to realize that the problem appears to be in the crossover.

I'm wondering if this is expensive to fix? Worth it? Can anyone comment?

The L26 is a nice sounding speaker. Caps and resistors for your crossovers are only a few dollars each, depending on the qualitly level of the cap. ( FYI) The LE25 tweeters can easily be blown at high levels.

Did you test your JBL LE25 tweeters out of the cabinet with an ohm meter or maybe even a 1.5 volt battery? I would think that the voice coil in the tweeters would let go before a fault would occur in the crossover.

[sneakyimp]

Thanks for the responses.

I am nearly certain it's the crossover because on one of the speakers, if I adjust the LPad with a screwdriver, the tweeter cuts in and out. If I jigger it just right, the tweeter comes on full volume. Additionally, I thought I had in fact blown the tweeters at first so I bought a replacement pair on eBay which were "working" and "removed from a pair of JBL L26 speakers".

On the other speaker, I also got the cutting-in-and-out behavior when adjusting the Lpad with a screwdriver. Unfortunately, it's a lot more finicky.

The bottom line is that I have a fairly strong hunch that there's something wrong with the crossover and I have at least one replacement pair of tweeters in my possession should I need a replacement. I don't have an ohm meter or any of the spray to clean the Lpads so I am wondering if it would be cost effective to take it to the local repair guy who's quite close. I know a crossover is not a particular complex circuit so I'm thinking it might be worth it to get that guy to look at it. If I can get them repaired for under $100, I think I'd be happy about that. Otherwise, I might as well buy some Klipsch KG4's for $200-300 or something.

[markw]

A can of deoxit would certainly be worth the investment particularly considering the money you've already thrown, and are planning to throw, at these.

[sneakyimp]

The problem is that I think at least one of the crossovers has more problems than just a dirty pot -- and I wouldn't even know what to do with a can of deoxit really. Just spray it in the front of the thing?

[cjpremierfour]

If you can get sound on both tweeters from both speakers, while playing with your pot's volume control, your crossover is problably good. This is just me and it may have some drawbacks, but I would run down to a local drug store and pick up some alcohol and try to get as much in the back of the pot as possible while turning the volume control.
There will be some little vents on the back of the pot that should allow you to get some alcohol inside the component. it's very possible that a dollar and the cost of gas may get your JBL's working again.

[sneakyimp]

I called the local repair guy and someone reassured me that crossover repair would be about $75. But then I drove over there and his wife tried to tell me it was going to be $170 for the pair. I'm now very crabby, having spent $75 for a pair of replacement tweeters that doesn't solve the problem.

I hope to try this pot cleaning but I think after that I'm about spent on these speakers. I'm fairly attached to them because they were my father's and I heard lots of good music on them for the first time. I'm nearly out of patience, though.

I'd like to be able to isolate the problem and make sure of a couple of things
* The tweeters are OK and not blown
* If it's the crossover, it's a dirty pot and not some other component.

Any tips would be most welcome. The crossover seems really hard to get at -- you can't open the back of the cabinet and removing the woofer sounds like a real chore. I can reach in and feel the crossover if I take the tweeters out, but I can't see anything. Advice welcome. I'm nearly at the end of my rope. For the time and money I'm spending, I could probably have purchased some old klipsch KG4's.

[sneakyimp]

Also...would WD-40 work on the L-pads or is that just going to catch on fire or something?

[cjpremierfour]

I called the local repair guy and someone reassured me that crossover repair would be about $75. But then I drove over there and his wife tried to tell me it was going to be $170 for the pair. I'm now very crabby, having spent $75 for a pair of replacement tweeters that doesn't solve the problem.

I hope to try this pot cleaning but I think after that I'm about spent on these speakers. I'm fairly attached to them because they were my father's and I heard lots of good music on them for the first time. I'm nearly out of patience, though.

I'd like to be able to isolate the problem and make sure of a couple of things
* The tweeters are OK and not blown
* If it's the crossover, it's a dirty pot and not some other component.

Any tips would be most welcome. The crossover seems really hard to get at -- you can't open the back of the cabinet and removing the woofer sounds like a real chore. I can reach in and feel the crossover if I take the tweeters out, but I can't see anything. Advice welcome. I'm nearly at the end of my rope. For the time and money I'm spending, I could probably have purchased some old klipsch KG4's.

No, Do not use WD40. Use need to clean electricial contacts ( Your Pot ) using isopropyl alcohol or another type of contact cleaner.

To test your tweeters: remove your tweeters, use a good know source of audio or a 1.5 volt battery
Connect your tweeter to the positive / negative sides of your receiver wires with the volume all the way down and your bass control all the way down ( below flat to take away bass ) SLOWLY turn up your volume control until you hear audio. ( DO NOT PLAY TOO LOUD or TOO LONG, just make sure it works and stop )
You can also use a 1.5volt household battery by hooking up a wire on both end and touching your tweeters terminals. They should click with every touch which would tell you the voice coil is not open.

You L26's crossover has (2) inductors, (1) 8UF capacitor and the (1) potentiometer per speaker. $75 per speaker is a complete robbery and you should avoid this guy. If both caps are blown, it shouldn't cost than a few dollars each for new 8uf caps. Potentionmeters cost just a bit more but can still be found starting at a few dollars. I would hope that contact cleaner would help the problem before you go shopping for anything.

The fact that you have tweeter sound playing with your pots volume would mean that your capacitors are good. If it was blown, you would have no signal to the tweeter at all.

***You will have to take out the woofer, you have no choice if you hope to find and correct this problem. You have to get to the pots in both speakers to pour or spray contact cleaner in both pots. It can not be done correctly using only your tweeter holes.

[sneakyimp]

Thanks so much for the detail, cjpremierfour. That sort of checklist sounds very helpful -- especially checking the tweeters. I'm aware that low-frequency, powerful current can damage them so I'll be careful.

I'm pretty concerned about getting a good look at the crossover -- I simply do not see how one might remove the crossover for repairs so I expect this must all be done with the crossover still mounted inside the cabinet.

Can anyone recommend any fundamental test on the various components (capacitors, inductor, etc.) for someone without an oscilloscope or any fancy gear? That schematic looks brutally simple and I can tell an inductor from a capacitor from a pot.

I have this sneaking suspicion there's a wire loose or something and would like to be able to check all the circuit connections.

[markw]

Before y'all get too far into the nuts and bots of this crossover stuff, check out post # 13 in this thread (http://forums.audioreview.com/amps-preamps/how-much-does-amp-circuity-design-affect-sound-35186.html#post379390"). Yep, it's the same guy. Methinks somebody's chain is being yanked.

[sneakyimp]

That other post (#13) is my post. Am I doing something wrong? I did minor in electrical engineering but it's been 20 years! I'm definitely not trying to fool anyone. I write software these days and haven't so much as looked at an oscilloscope or multimeter since college.

[markw]

That other post (#13) is my post. Am I doing something wrong? I did minor in electrical engineering but it's been 20 years! I'm definitely not trying to fool anyone. I write software these days and haven't so much as looked at an oscilloscope or multimeter since college.I just fined it very strange that you can come off as so knowledgeable and eloquent in that post and then appear here as an ignorant, clueless junior high kid playing with his daddy's' equipment.

For an engineer, even 20 years out, to not know how to inject contact cleaner into a pot is a bit much, doncha think? :rolleyes: Technology hasn't changed that much, and those speakers are 35 years old anyway.

If I wasn't so kind, I might suggest you''re just trolling.

[sneakyimp]

I think you've more than suggested I'm trolling. I assure you I am not. You have a good point about the other post and this one not really matching up. I'm not sure what to say in my defense. I had to post 5 times before I could make my own thread so I bravely ventured into perhaps the wrong thread and tried to sound smarter than I am. I hope I can be forgiven for that -- although the post was very heartfelt and based on years of non-technical experience. There is magic in the old analog circuits that just doesn't exist in the digital ones. And, if you force noobs to post in existing threads before they can ask their first question, you are likely to get stuff like that.

As for being an engineer, I'm a software engineer. I have never worked as an electrical engineer or any other hands-on type of electrician/circuit designer/repair guy. I've assembled my past 5 computers from the basic components and I've never once encountered a dirty pot or crossover. I'm also an amateur plumber when the pipes back up.

I did lots of time with circuits in college (mostly just simple one-transistor amps, frequency filters and logic circuits built from pristine new parts) but I have no experience (and no business) at all troubleshooting real audio circuits in vintage equipment. I'm familiar with scratchy pots on a guitar or a guitar amp, but have always just turned the knob up and down until it clears up -- and most of the pots I've seen are fully enclosed. I.e., no vents on the back as described here. I certainly don't have any hands on experience tearing down a crossover on some old speakers. I just haven't put in the time.

I have inherited my father's old speakers, I have invested way too much in trying to get them running again. I've taken them to two very reputable repair shops and have been quoted outrageous amounts of money to get them fixed -- one shop wanted $400 to have the tweeters re-coned. In retrospect, I don't think they even checked to see if the tweeters were blown, which pisses me off.

My experience (what little I have) tells me that it feels like a short rather than a dirty pot because rather than the sound cutting in and out as I sweep the pot back and forth, the circuit only connects for the tweeter at very very very specific locations in its range. On one speaker I can get it to more or less play steadily. On the other, I got some noise out of the tweeter a couple of times but it has since given up. This sounds to me like a bad solder job, a short, a fried component...something like that.

I do sincerely appreciate the advice and will likely give it one more stab. I almost bought an ohmeter today from newegg. Any advice about a methodical approach would be appreciated. If we can isolate a bad component, I might be able to replace it -- although the goop (hot glue?) covering the inductors looks tough to deal with.

[markw]

I was only an appications programmer, working in several vertical markets,from1983 to around 2001 so I really can't lay calim to being a "software engineer" but that doesn't mean I forgot my schooling as an electronics tech in the mifd seventies. You can't tell me you've totally forgotten everything youlearned.

A pot is a pot, be it in a guitar amp or a speaker crossover. I'm very surprised that in your long career as a musician you've never had to spritz a pot.

[sneakyimp]

I've never spritzed a pot (linear, exponential, ganged, or unganged) in my life. My approach has always been the twist-left-twist-right-repeat-ad-nauseam technique.

Sorry if I seem suspicious. Guess I'll try and follow instructions. One pot spritzing coming up.

[sneakyimp]

OK so I took the woofer out and snapped some photos of the inside. The pot has no vents on it as far as I can tell and the components all appear to be mounted on a piece of particle board which is glued and stapled (WTF??!) onto the inside of the front face of the cabinet. Seems to me if I need to make any repairs, I'll need to take the components out. Any suggestions about how to remove this without damaging anything? Obviously, the plan is to eventually return the components to the inside.

Based on the circuit diagram (thank you, cjpremierfour, there seems to be a bigger one here (www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/technicalsheet/L26 ts.pdf)), I believe the parts correspond as follows:
* 8-ohm pot - silver can on the left, duh
* 1mH inductor - coil stuck under the hotglue/glob of goop bottom center
* 0.5mH inductor - coil exposed near the insulation to the top
* 8uF capacitor - carboard tube on the right (with the part # stamped on it duh)

I tried the simple low-volume-no-bass test on all 4 tweeters. The new ones (LE25-4) work. The old ones (LE25) do not. It would appear that the speakers suffered some trauma -- at least enough to blow the tweeters, which may explain something about what happened to the crossovers.

I ordered a multimeter from newegg which will hopefully help with circuit diagnosis.

Any tips would be much appreciated. I'm wondering if it might not be easier to buy/build a new circuit like the one recommended here (http://www.troelsgravesen.dk/JBL-L26.htm).

[sneakyimp]

It looks like the problem with the other speaker crossover is pretty simple. One of the solder terminals on the L-pad has broken off. It looks like I'll need to replace at least one pot/L-pad (where to get?) and it also looks like I'm going to have to remove the crossover board (how to do this?). Any suggestions welcome.

[sneakyimp]

OK I managed to remove a crossover by applying tons of elbrow grease. I found a new one on eBay.

Am I really going to be ignored here?

[cjpremierfour]

JBL didn't install their crossover to be user friendly. They were glued very well to the cabinet and also sometimes glued across the components to keep them in place.

Sometimes, crossover boards will break on removal. You will have to work it up slow with different lenght screw drivers until it breaks free. Good Luck with that!

You can find any and all crossover components at a website called: Partsexpress.com.

If you already have the crossovers out, I would go ahead and replace the 8uf cap in both speakers. The cap's may be good but if you plan on keeping them much longer, I would go ahead and replace those caps with what ever "Hi End" 8uf cap they have on sale.
If cleaning your pots hasn't made them useable, I would go ahead and replace them too.

[sneakyimp]

Thanks for your response, cjpremierfour. The one crossover I have managed to remove is in a million little pieces. The components are more or less intact but the pot is in pretty sad shape -- it was the reason I chose to try and remove the crossover in the first place. I purchased a complete replacement on eBay for about $20 -- apparently JBL started to use screws instead of glue later so mounting it should be pretty easy. I appreciate the tip on the capacitor -- what advantage would a newer cap bring?

The other big question I have is about mounting the new crossover. I will obviously drill holes because the new xover comes with mounting screws, but I'm wondering if I should put some damping material between the new xover and the cabinet wall to minimze any potential vibration. Suggestions for material are quite welcome. Paper comes to mind.

I expect I'll probably try and rip out the other crossover too and buy a replacement for it also. I just don't see how I can perform any soldering or repair while the xover is in the cabinet :(

[cjpremierfour]

It wouldn't hurt anything to dampen the back of the crossover to the cabinet. I would think almost anything that would compress would work.
As far as replacing the caps, old caps can sometimes dry out and change the sound of your tweeters. However, your JBL L26 have a cap that has a form of wax around the ends to stop this from happening. Over the course of time, it is possible that it could leak. It may be OK, but if you plan on keeping them for a long while, ( like 10 more years ) I would go ahead and spend the money to replace them.
I wish I could say that new caps would open up the top end, make bad recording sound better or clear up the sound stage. If your caps have leaked, this is possible, but more than likely, you will not be able to tell much difference. It's just something that you may have to do down the road.

[sneakyimp]

I was unable to find any 8uF caps at Partsexpress.com. The closest they have is 6.8.

I did find this 8uF cap (http://thetubestore.com/ca-at-8uf-450v.html).

The upside of removing the old crossovers is that I can install new ones with a more sensible mounting scheme.

[cjpremierfour]

I was unable to find any 8uF caps at Partsexpress.com. The closest they have is 6.8.

I did find this 8uF cap (http://thetubestore.com/ca-at-8uf-450v.html).

The upside of removing the old crossovers is that I can install new ones with a more sensible mounting scheme.

That would work fine. I was hoping that you could find a pair on sale at Partsexpress. $6.60 each isn't bad, sometimes Partexpress will have them in the $3.00 each range. With them not having the correct value, that seems to be a good fit.

I'm just hoping that you can tell a before and after difference. Keep in mind, the wax sealed caps may still be OK. I'm just saying, down the road, the caps may start to degrade.

[sneakyimp]

OK first of two replacement crossovers arrived in the mail today. I put it in and it sounds pretty good! woofer works, tweeters work. I hear a tiny bit of distortion here and there, but I think it might just be the nature of the speakers. They are a 40 year old design, after all. I think it might have something to do with the bump in the woofer response and the sort of wonky crossover design as described here (www.troelsgravesen.dk/JBL-L26.htm).

Because the new crossover was from a new model (serial number 177750 -A), I had to drill 4 holes in the front panel of my speaker which is an earlier build, serial number 87709. I didn't mind at all, though, because it will make things easier to replace if something goes wrong with the crossover again.

[sneakyimp]

I'm happy to report that I was able to buy two replacement crossovers and install them and the speakers are working swell now. My speakers, which are the older L-26 models, had their crossovers *glued* and *stapled* to the inside of the front face of the cabinet. Ripping out the crossovers was hard until I figured that the key is to scrape a bit with a razor edger or spackle spatula until you meet a staple and then pull out the staple. Pliers work for staple-pulling, but you have to be careful not to smash the cardboard port tube.

I also had to drill mounting holes for the replacement crossovers -- this is pretty exacting work and one must be pretty careful.

Thanks for the suggestions guys. :thumbsup:

And markw, this one is for you: :dita:

[markw]

And markw, this one is for you: :dita:Gee for such a knowledgable tech you sure are a drama queen and a crybaby to boot. All you needed was to spritz the pots or, at most, new pots.

[sneakyimp]

Gee for such a knowledgable tech you sure are a drama queen and a crybaby to boot. All you needed was to spritz the pots or, at most, new pots.

Unfortunately, the pots were more or less stuck in place (corroded, etc. -- moisture?). One of them had broken loose and would turn around completely when you tried to turn the adjustment. So minimally new pots.

I don't know if you were paying attention, but the crossovers were *glued* inside. Not only am I not in possession of mirrors/cameras/arthroscopic surgery equipment, but the nut holding the old pots in place was on the other side of the glued-on board. To unscrew the nut would require that I remove the crossover anyway. Removing the crossovers was impossible without tearing them to pieces.

For such a self-professed elitist you sure do provide a lot of factually inaccurate detail and grief to well-intentioned posters. I think you are the troll.