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View Full Version : Decade L36 woofer rattle



timothyone
01-01-2009, 04:43 AM
Hello all! Ijust picked up a pair of old L 36 decades that I've looked for since the very year they were first made. Couldn't afford them, then couldn't find them. Now that I have them I find they are exactly as I remember them so long ago, except that one woofer has a small rattle than appears with bass notes. I don't know when but they have had new surrounds added, and it looks like they did the jib without removing the old dust covers. The woofers move right, and with no obvious voice coil rubbing sounds. If I very gently place a finger on the cone it stops the rattle from happening. Does anyone know if there a common problem with this woofer that could cause this?
Thanks, and thanks to the site for being here for us, I really enjoy it!

clmrt
01-01-2009, 06:03 AM
If the voice-coil leads are too close to the cone, they could touch at certain times and cause noise. Remove the woofers to see that the leads are away from the cone.

lgvenable
01-01-2009, 10:10 AM
When I've worked on a few woofer surrounds,I have heard a slight rub or even (as in your case) perhaps a slight rattle. (in an acquired speaker)

The giveaway (to me) is the when you touch it lightly on one side of the surround, the sound stops.>>> It sounds like the woofer need to be re-surrounded, and then care given as the glue dries and the 30HZ tone is played to maintain the surround position to eliminate the sound.

With careful positioning,you could probably get rid of the rattle as the surround glue dried. I have two sets of L26's, which I got off eBay and Craigslist. One of them had severe VC rubbing, to the point of making the woofer unrepairable (ie recone).

In place of the standard copolymer glue I used 3M 92 spray glue, which I sprayed in a dish, and then applied under the new surround edge with a artists brush.

I clamped the surround in 12 spots around the outer edge, holding the surround down to the basket by clamping it. I was able to gently work around the surround edge, and like you find the sweet spot where a slight touch resolved the speaker rubbing/rattle.

I adjusted the small c clamps until the woofer played fine with no sound except the 30HZ tone. I then started turning the outer edge of the surround (between the clamps ) up, and gluing it down with the brushed on 3M92 glue. It dries very quickly, and if yu have to be careful, or you can slightly swell the surround.

If that happens allow the glue to dry, and as the offending solvent that swelled the surround evaporates..the swelling and distortion will disappear. Remember, several small applications of glue are better than one really thick one.

I use MEK to cut (dilute) the 3m 92 glue and get a fast drying smooth application.

I got to where I applied the glue to the basket, and after allowing the glue to dry, pressed the surround down into the highly tacky glue, seating the surround permanently. I did this and worked around the surround circumference.

The small c clamps allowed the surround to be maintained in the EXACT position where no VC rubbing or extraneous noise was heard. After allowing the 3M 92 glue to dry with the surround for a day, I was able to remove the clamps, and then followed with a liberal bead of co-polymer type vinyl acetate glue (what they give you with your surrounds) was applied

Finally you pressed the new gasket around the speaker, or if you saved them the original one you have to remove as you start the re-surround. Naturally, as you do this process you maintain a continuous 30HZ tone being played by the woofer, which will keep you from screwing up; and let you ascertain by ear the the vc is properly centered.

If you have access you can also use Air Products Airflex 7200, a high solids (~72%) of Airflex 400, both of which are tacky co-polymer type PVA based glues. (the very glue they give you when you buy the surrounds to do the re-surround yourself.

The method worked so well, that I was able to use it on 15 and 18" drivers as well, with perfect results. especially in those cases where I thought the surround was 3/16" too short. You are able to use a small ruler to position the surround evenly as it is glued down.

Obviously this mod of the standard re-surround method, require that the first thing you do is to glue the inner edge of the surround to the inside outer edge of the cone.

For this it is ideal to use the water based co-polymer glue, as it is the best glue for applying the foam surround to the paper cone and getting a perfectly seated application. Afterward you can use the above modded method to glue down the surround outer edge to the basket.

Again, it makes the 30HX tone method bullet proof, and since the glue dries very fast, it doesn't take nearly as much time as using the co-polymer type glue to seat the surround to the basket.

I have used both 3M 92 glue and 3M 90 glue with this method.

After the surround is completely attached I'll take 5 ml syringe with a blunt needle (not a sharp needle, but one which has no sharp tip). Then, by gently working around the inner edge of the cone, I apply a bead of glue to the cone outer edge and the foam surround inner edge to help make sure the cones outer edge is sealed perfectly to the surround. If need a (only slightly) damp wash cloth can help smooth the glue down, so you have smooth transition from cone to surround.

In all this follow one rule;

Take your time and be patient, and allow the glue to completely dry. I've had great results this way; but if I did it this way to make a living I'd eat beanie weinies...as it time consuming. In the end, my results have always been as good (if not better) than those where I sent a speaker to the repair shop, and had then do the re-surround.

FYI..the L26 I did this to >> is now on year 5 after the re-surround, and can be played at the full rated power without any sounds liike vc rubbing (or a rattle). That's pretty amazing to me, as it was originally so bad I thought it unrepairable . I mean it was REALLY REALLY bad.

SEAWOLF97
01-01-2009, 10:22 AM
I had an M&K sub that needed a new surround when I acquired it ...went thru the whole procedure and installed a new one ..no VC rubs. BUT , when played, it rattled too. Did the same thing, putting a finger on different spots all around, and one stop stopped the rattle....so I marked that spot and stripped all my new foam off to start over.

this time I only glued the marked spot only and applied a little outward pressure, when that dried, I glued all the rest of the surround. Works perfectly now. Daily use. :applaud:

timothyone
01-01-2009, 10:47 AM
I thank You both for the great and quick responses! You can definitely meet the best people here on sites like this one and Audiokarma! :) I just wish I had a few of you guys in the neighborhood, boy would it be great to have an audio club where a gang could meet and share ideas and do show and tells!! LOL! You know what I mean, like bring in tuners and receivers, or pictures of old girlfriends long before they were shipped off to the nursing home!

I only paid $113 for the pair on the bay as they were local, so I am surprised to find only one serious problem. I have done two pairs of surrounds before, and they both worked out well, but I did remove the dust covers and use spacers on the coils. I hate to do that with these because I don't know of anywhere to get those L36 covers, and I really like that look. Looks seldom matter to me, but these and that look have been in my heart a long time.

I was in the Army in Hanau Germany in an Artillery unit, and a roommate bought a pair. After a little wine (I think that was all, but I really can't remember everything from that time period:o:) that Pink Floyd sounded so good on those JBLs I swore I'd someday get some! I made the same oath about a particularly sweet and georgious bar girl, but had to break that promise to myself after she disapeared for a year and reapeared as an insane witch. She must have died after I left Germany because I could swear I married her incarnate self several years later:( I always wanted a wife that made real good money, and that's just what I got! :blink:

I'll post the results after I tear into this thing. I've waited 35 years, I can wait another few days.

toddalin
01-01-2009, 10:58 AM
Simple and free, you may be able to orient the speaker differently within the cabinet (i.e., turn it around to a different position) to alleviate this problem.

timothyone
01-01-2009, 06:38 PM
Do the surrounds on the 123a woofer attach to the inside edge or the outside? It seems the ones I've seen before were inside, but these I have here have been glued to the outside. I was wondering if this might cause my rattle problem. It only happens in one woofer, so far, so maybe not???

I'm sitting here listening to the new James Taylor cd "Covers". It's a good JT album. Well produced, and his voice is as good as ever. Years from now when I'm sitting in a nursing home with alzheimers I'll probably still be sending people out to buy the newest JT cd that he'll record in the recording studio he'll build at his nursing home.

I must be out of touch with modern music because I only know a few of these "covers". I have the bass turned down and am having no problems at all with the woofer, and I'm playing it on my Sansui 9090 loud enough to hear across the house and in my bedroom. Even up close I am hearing nothing but great clear sound as long as I keep the bass down to about 9:30 on the dial. If I turn loudness on it immediately begins to have small, light rattles with bass notes, and even pops with big bass hits. I like it with little bass with most music because I've lost so much of my high frequency hearing, but some of my soul and hard rock would burn out this voice coil, so I have yo fix it somehow.

Getting these JBLs was a little like having a new baby that has a birth defect.:o: Might cause problems, but I'm still gonna name him Little Timmy and tuck him in at night all the same. :baby: Did I mention that I'm nuts about my audio gear?

mech986
01-01-2009, 07:00 PM
Another thing to check although it doesn't happen often is the attachment of the spider circumference to the frame. Sometimes these come loose at some point around the frame circle they attach too. They then flap at certain frequencies or levels.

You'll have to pull the woofer(s) in any case to check on how they are playing in or out of the box.

Wait, why are you asking about the 123A woofer? That's the woofer that is used in the L100. Your L36/L36A should be either the 125A or 125H. See tech sheet here:

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/L36%20Decade%20ts.pdf

Pretty much 98% of all the vintage woofers had the surrounds placed on the back of the cone as OEM. A lot of resurrounds get placed on the front (its somewhat easier and faster). For many of us here, it is important to get them placed on the back for aesthetic and performance reasons (correct static position and symmetrical travel through the magnetic gap field).

If you need a replacement, the 125A/H models and the equivalent 127A/H do come up on the 'Bay. If possible, get the "H" Ferrite models as they are lower in overall distortion compared to the original "A" Alnico models.

Bart

timothyone
01-01-2009, 08:10 PM
I read so much on these JBL models that I get the numbers scrambled in my head. It's similar to when I call one grandbaby by another grandbaby's name.

I tried turning the woofer one screw distance to the right and it really does make a difference, but not a complete fix. Some of my good stuff still makes it rattle or hum a little.

I don't know if this is a simple matter of common sense, of which I may lack, or if it is indicative of the problem, but when I hook it up to a Sansui 4000, which is about 50 watts per, it sounds great. I can add all the bass and loudness I want and no rattles. The bass on the 4000 is naturally lower than with the 9090, but I am using much more than what I use of the 9090s bass. Could the 9090 be sending unclean signal to my speakers, or some such? Is it just the lower power? My HPM 60s sound good with the 9090, so I would guess that's not it. These are rated at 50 watts continuous, and I was probably giving it more than that much of the time. The funny thing is, I was cranking it much louder with the 4000 because it was not causing problems.

One thing I've learned from this is just how good the 4000 is. With these JBLs it sounds every bit as good as the 9090 with the treble turned up. I knew it was decent, but now I see it as one of Sansui's best. I have a 2000 I think I'll hook up to the JBLs and see how that sounds. I am falling ever deeper in love with Sansui and JBL. I am no longer giving that one to my son. He'll get an old Pioneer 9000 instead, or maybe a newer black plastic Sony that really impresses the kids. I can remember a time when I didn't know good stuff from bad. (I guess that explains the marriages too!)

Tomorrow I order surrounds just in case. I alrerady need them for another pair anyways. I get them from loonytunes2001, who I learned about on this site.

timothyone
01-01-2009, 08:16 PM
I got that pdf file. That will be of tremendous help now and in the future.

timothyone
01-01-2009, 09:36 PM
I pulled that 125a again. I put my glasses on this time and noticed that one section of the new surround had pulled loose. When i gave it a gentle tug with a flat screw driver it began to almost fall off the cone. It came completely off as if it had never been glued. Now the worst part: When I exercised the woofer it hung up and got stuck at one point for a few secs. I take that to mean the coil has been overheated and is now no good. After [laying with it awhile it loosened up, but it is still not right.
Well, now I'll have a well made speaker to play and learn with. I think I'll replace it when I find one, and then try to do a recone on this one. Even burned out I'm exited to have one of these great old drivers to deal with.

Does anybody know what is used to remove the spider? Is it just yanked out, or is there a certain way it's done? Are there chemicals to unglue these things? Ripping it out would feel too much like attacking an rare antique.

Am I wrong in my assumptions and plan?

hjames
01-02-2009, 06:17 AM
the worst part: When I exercised the woofer it hung up and got stuck at one point for a few secs. I take that to mean the coil has been overheated and is now no good. After [laying with it awhile it loosened up, but it is still not right.
Well, now I'll have a well made speaker to play and learn with. I think I'll replace it when I find one, and then try to do a recone on this one. Even burned out I'm exited to have one of these great old drivers to deal with.

Does anybody know what is used to remove the spider? Is it just yanked out, or is there a certain way it's done? Are there chemicals to unglue these things? Ripping it out would feel too much like attacking an rare antique.

Am I wrong in my assumptions and plan?

I would say yes, you are wrong in your plan.

Its one thing to replace a surround when the foam crumbles, but for most folks, anything further is too sensitive for beginners. Besides, JBL doesn't sell replacement cones and such to customers. Its too easy to get it wrong.

You can buy a used replacement woofer of unknown condition on eBay, of course, But your best bet is to get in touch with a pro and let them examine it, and, if needed, recone it for you, with new voicecoil, spider and cone.

There are folks here who have good reps and do such work, Edgewound in CA, Gordon in Atlanta, and plenty of others ...

I'm sure they'll chime in shortly ...

LRBacon
01-02-2009, 01:21 PM
I pulled that 125a again. I put my glasses on this time and noticed that one section of the new surround had pulled loose. When i gave it a gentle tug with a flat screw driver it began to almost fall off the cone. It came completely off as if it had never been glued. Now the worst part: When I exercised the woofer it hung up and got stuck at one point for a few secs. I take that to mean the coil has been overheated and is now no good. After [laying with it awhile it loosened up, but it is still not right.
Well, now I'll have a well made speaker to play and learn with. I think I'll replace it when I find one, and then try to do a recone on this one. Even burned out I'm exited to have one of these great old drivers to deal with.

Does anybody know what is used to remove the spider? Is it just yanked out, or is there a certain way it's done? Are there chemicals to unglue these things? Ripping it out would feel too much like attacking an rare antique.

Am I wrong in my assumptions and plan?

Hi timothyone,

I assume you excercised the cone manually?

There isn't a lot of room in the gap. With the one section of the surround not doing it's job, the voice coil will not be properly centered and will hang up or rub quite easily. I would wait until you get the new surround kit, use the special polymer glue to re-attach the section of the surround to the cone and then use the 30 Hz tone cd to proper align the voice coil in the gap while the glue dries. You may end having to replace the surround(s) if they weren't properly installed.

Larry

timothyone
01-02-2009, 09:16 PM
Hjames says I may simply need to redo the surround, and that i will try. Go with the cheapest idea first is a good idea. Thanks

LRBacon says to hire a pro. I think I'll do that once I try the resurround.

The thing is doing real well now, as long as I don't give it the bass. Bass at 12 o'clock does well. And it does really well with a lessor powered receiver, but not as well as the other one.

The woofer was sticking only at the point where it was furthest from the magnet. Every other I have tried to pull out that far went smoothly all the way in and out. This feels like it is meeting a larger section of voice coil, as if the bottom of the coil is somehow wider than the rest.

Again, Thank you. It's sure nice to have guys like you around. Makes the hobby so much more enjoyable.:)

rek50
01-03-2009, 09:12 AM
" Could the 9090 be sending unclean signal to my speakers, or some such?"

Yes

Electrolytic capacitors drift in value (uF) over time...Change in
Bias/Offset. Resistors can quit. Relays can fudge up.

Controls/Switches (Bass/Treble/Balance...) get dirty over time. (Deoxit)

Full Bass with Loudness activated will reveal :barf:

hjames
01-03-2009, 09:58 AM
Hjames says I may simply need to redo the surround, and that i will try. Go with the cheapest idea first is a good idea. Thanks

LRBacon says to hire a pro. I think I'll do that once I try the resurround.


Actually, you have us reversed, but what the hey?

timothyone
01-04-2009, 02:24 PM
the ones I used to listen to in 1974, they helped persuade me to try things that may have permanently reversed parts of my mind. And I may be getting flash-backs listening to these new ones. :blink:

hjames
01-04-2009, 02:29 PM
the ones I used to listen to in 1974, they helped persuade me to try things that may have permanently reversed parts of my mind. And I may be getting flash-backs listening to these new ones. :blink:
Yeah, the joys of Yes, the Dead and all of that on 4310s back in the day
are what encouraged me to get my pair of L-36s in '76 ...

Kept them 30 years until I found this site and got bigger ones!

timothyone
01-04-2009, 02:32 PM
" Could the 9090 be sending unclean signal to my speakers, or some such?"

Yes

Electrolytic capacitors drift in value (uF) over time...Change in
Bias/Offset. Resistors can quit. Relays can fudge up.

Controls/Switches (Bass/Treble/Balance...) get dirty over time. (Deoxit)

Full Bass with Loudness activated will reveal :barf:


I have considered having it recapped since I got it. It sounds great, but it seems to be a little weak in FM reception. I'd like to see if I'm missing anything. May as well as long as I have one. Took me long enough to get. Anybody have the name of a good Sansui guy in the Kentucky area. Anywhere close to Louisville would be great. Thanks!!

timothyone
01-04-2009, 02:38 PM
Yeah, the joys of Yes, the Dead and all of that on 4310s back in the day
are what encouraged me to get my pair of L-36s in '76 ...

Kept them 30 years until I found this site and got bigger ones!


But then I used to dream of being John Holmes, so I learned to dream more reasonably!

I would like to stuble upon a pair of L100s or L112s or even L200s one day. I have to keep it cheap though, because I have 9 grandbabies who all have a really special way of opening Pawpaws wallet. ;)

Audiobeer
01-04-2009, 04:49 PM
Is your 9090 a DB version? The 9090BD was notorius for having problems with the Dolby board. Easy fix! They sound great once the caps and cold solders and resitors are updated & resolved.

rek50
01-05-2009, 06:04 AM
Some info about Sansui 9090, 9090DB...

http://www.audiokarma.org/forums/forumdisplay.php?f=39