JBL 123A Voice Coil Rub

[malden]

I was listening to my L88's hooked up to a Marantz 2330B receiver at a moderate listening level today when one speaker started to cut out. Not knowing if it was the receiver or the speaker I swapped the speakers from right to left and sure enough, it was the speaker. Gently pushing in on the woofer dust cap, I could feel the voice coil rubbing.

Is there any hope of having it repaired? They are mint condition.

[Eaulive]

If it was cutting out, I doubt it's the voice coil rubbing, I would check the connections (cat wiskers) from the cone to the push connectors, a bad connection can create a scratching sound when you move the cone under load (i.e: connected to an amplifier output.)

[malden]

Thanks, I'll pull the woofer out over the weekend and take a look.

[malden]

For some reason, the speakers have been fine for the past few weeks, but yesterday, I hooked them up to a different amplifier and the same speaker started to cut in and out again. I pulled both woofers out to look at the x-overs and it looks as though one of the capacitors is bulging at the top, the cap in the other x-over is flat.

The x-overs in my speakers consist of only a 8 ohm L-pad and one capacitor that has no value stamped on it.
Does anyone know what the correct value is?

[malden]

Well, I did a little web browsing and came across this thread...

http://forums.audioholics.com/forums/diy-corner-tips-techniques/23914-jbl-xover-cap.html

looks like the value of the capacitor (part number 10391) is 8 uF, just thought I'd pass it along...

[BMWCCA]

Yeah, what you need is also linked to from this site's library:

http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/technicalsheet/L88%20nova%20ts.pdf

[malden]

The link you posted seems to be for an earlier L88 model. I posted the same schematic in post #4 just for comparison. Compare it to the photo I posted, they are completely different crossovers.

[hjames]

That looks like the satellite board that would mount on the baffleboard behind the foilcal.
That has less parts than the schematic shown as correct.
Where is the rest of the crossover?
Have you followed the wiring within the cabinet to confirm that's all there is in there?

Are you the original owner and can you confirm it has not been "improved" by a previous owner ... (such things happen)

Perhaps you should add the parts shown in the schemo to make it match the specified design?


For some reason, the speakers have been fine for the past few weeks, but yesterday, I hooked them up to a different amplifier and the same speaker started to cut in and out again. I pulled both woofers out to look at the x-overs and it looks as though one of the capacitors is bulging at the top, the cap in the other x-over is flat.

The x-overs in my speakers consist of only a 8 ohm L-pad and one capacitor that has no value stamped on it.
Does anyone know what the correct value is?

[malden]

As far as I know, they are original. There are no other components inside the cabinets except for the drivers. I have 2 sets of L88's, a much earlier version and the pair in question. The earlier version has a crossover that matches the attached schematic and is also behind the foilcal.

There is currently an online auction for 2 pairs of L88 crossovers and they both look identical to the crossover in the photo I attached.

The thread that I linked also confirms that there was more than one version offered by JBL.

[hjames]

As far as I know, they are original. There are no other components inside the cabinets except for the drivers. I have 2 sets of L88's, a much earlier version and the pair in question. The earlier version has a crossover that matches the attached schematic and is also behind the foilcal.

There is currently an online auction for 2 pairs of L88 crossovers and they both look identical to the crossover in the photo I attached.

The thread that I linked also confirms that there was more than one version offered by JBL.

So - I gather you are not the original owner?
And you do not know if they have been tweaked before you got them?

I also gather there is no labeling on the yellow cap shown in your photo?

From what I have seen, JBL made running changes to improve a product (based on some of the dated charts for the Pro speakers).
Why not revise the crossover to the same design your other pair has?
Get the correct caps from a supplier, put them in the circuit and be done with it.

[malden]

I think it's obvious that I am not an authority on the L88's or JBL in general. I provided the information I have which may or may not be conclusive.

If you are trying to make a positive contribution to this thread, please provide some useful information.

[hjames]

I think it's obvious that I am not an authority on the L88's or JBL in general.
I provided the information I have which may or may not be conclusive.

If you are trying to make a positive contribution to this thread, please provide some useful information.

Gently gently ... I am not trying to ding on you - you just said "As far as I know, they are original."
and I was trying to find out specifically if you were the original owner or if you bought it used.
Either way, there is no need for anger, lots of us own speakers we did not buy new.

But the L88 was a lower price model - so if the caps have no writing on them, and it seems like its not a
well documented variation of the production version, I'm guessing you can go buy an 8 µF metalized polypropylene cap
from Parts Express (part 027-426) or Madisound like that other thread suggested.
http://forums.audioholics.com/forums/diy-corner-tips-techniques/23914-jbl-xover-cap.html
It seems to me like the best approach would be to make it match the documented version of that speaker.

That's all I am trying to get at here ... no flames meant.

[malden]

I know nothing about electronics but I just realized that the capacitor is probably a "high pass filter" and has no affect on the woofer.

Can someone please confirm this?

[malden]

If it was cutting out, I doubt it's the voice coil rubbing, I would check the connections (cat wiskers) from the cone to the push connectors, a bad connection can create a scratching sound when you move the cone under load (i.e: connected to an amplifier output.)

I came across a website the other day where someone reconed a 123A-1 because the voice coil was rubbing only to find that the foam filter inside the magnet assembly had deteriorated and some had got lodged in the voice coil gap. Can't find the link but will post when I do.

[malden]

Found it!...

http://ka7oei.blogspot.com/2013/01/dang-it-jbl.html

not sure if this pertains my driver...

[malden]

here's the flipside of the x-over. The model number was hidden between it and the rear baffle it was attached to

[kippers]

So, the voice coil is rubbing.
So, you have a mechanical rub? so it will be a mechanical problem and solution so I wouldn't worry about the cross over network.
The post on the foam deterioration is spot on and the probable cause of your woes. Ihave the 2213h and it suffers this same problem.
Take the speakers out and remove the metal plate with the serial number and wire mesh on the back of the magnet, get a torch and have a look into the hole.
If you can see foam it has not deteriorated....yet, so remove it before it does! (use your finger and a vacum cleaner)
If you can see the back of your dustcap.....it's too late! and you have your answer.

You can fix this problem by removing the dustcap and cleaning between the voicecoil and magnet. I think the easiest way to do this would be to just pour in isopropyl alchohol whilst moving the cone up and down, this should dissolve the deteriorated foam restoring the gap to normal operation. The Isopropyl Alcohol will evaporate and should cause no damage if you are careful not spill any on the cone itself as it will soften other adhesives, so you would need to be quick, don't want to soak, just a quick rinse.
The more brutal method, if you don't want to remove the dustcap, would be to cook the speaker, literally put it on an electric hob and gently heat the basket of the speaker through the magnet up to the point where the deteriorated foam will melt, this will be at a lower tempreture than the other adhesives used in the construction of the speaker would melt or burn, but you have to be really, really careful, heat it up too much and your driver will be ruined.

If you own these speakers then you need to get that foam out before it kills your speakers, should be a massive sticky on this which lists all the affected divers. Assertive, preventative action now will mean you can enjoy these woofers for years to come.

I've just checked my other 2213h driver, which just arrived today, and have discovered it has this problem, so I shall be working to remedy this today.

[malden]

Thank you for the thoughtful and informative post, kippers. I have a beat-up 2213 that's in need of re-coning so I will practice on it first.

Heating the speaker seems to be a last resort solution, I would be worried that the foam would gum up. Have you tried that method?

[kippers]

Well the problem is that the foam is already gumming up through deterioration, it becomes gummy and weak, falls away from the adhesive originally holding it on, it breaks up and bits get stuck between the VC and Mag. What is left of it will harden eventually but until then it is rubbing and gumming up the voice coil gap. Heating it up speeds this deterioration up and flattens the gummy residue out restoring the gap, I have my 2213h on the hob (number 2 setting) as we speak in order to remove the metal badge and get a better look. You can't use a hot air gun or hairdryer to soften the glue holding on the badge as you would just be blowing everything into the voicecoil magnet gap. So just heating it up enough to get the badge off and then I'll get the vacum and my finger into it and see if that is enough to fix it. Heating it up to get the badge off might in itself be enough to cure it, but when it cools I'm still going to use an artist brush my finger and the vacum on it to be sure nothing else gets in there. When it's all done I'll get a new bit of foam and insert it and stick the badge back on, good as new!
If anyone is mad enough to use my methods you need to remove eveything that could melt or destort, on the 2213h there is a rubber ring around the magnet (easy to take off and on) and the terminal posts as they use plastic washers to isolate from the speaker basket. I'v had on number 2 setting on my hob for 15 mins and hot enough to take the badge off and you can still use your hands to hold the speaker at it's outer edges, but the magnet will be hot where the badge is.
Been doing this as I've been writing this reply and glad to say that most of the foam came out in one piece with the vacum, still a bit hot to get me finger in to rub the edges and get it all out but 20 mins we should be good.

[kippers]

Hmmm, just had a look at pictures of your drivers and they are totally different from the 2213h, so problay my info is for another thread. Your drivers have alinco magnets, so wouldn't recommend heating them up. Looks like the magnet cover or possibly magnet itself is held in place with 4 screw head bolts?
Not sure if your drivers ever had foam inserts, none in the pictures I'm looking at.

[malden]

Thanks for the update. I'll take a look at my drivers over the weekend.