Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 31

Thread: JBL L20t3 woofer surround

  1. #16
    Senior Member SEAWOLF97's Avatar
    Join Date
    Jan 2006
    Location
    sheltering in place
    Posts
    9,892
    At Intel , we had a saying .... "If it ain't broke, fix it ..till it is"

    I like K's suggestion
    It's the new Mother Nature takin' over
    She's gettin' us all, yeah, she's gettin' us all

  2. #17
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    Quote Originally Posted by SEAWOLF97 View Post
    At Intel , we had a saying .... "If it ain't broke, fix it ..till it is"

    I like K's suggestion
    Earl K or Kay Pirinha? If Kay Pirinha, then yeah, that's the route I will go here.

  3. #18
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    I went at the surrounds with Dawn dish liquid in warm water. Seems to have gotten rid of most of the crap. They are still a bit tacky but then so am I.Name:  IMG_7917.jpg
Views: 92
Size:  79.3 KB
    Since I have these opened up, would it be to my advantage to replace the 31 year old capacitors or am I opening up a can of worms here with that suggestion?
    Attached Images Attached Images  

  4. #19
    Senior Member grumpy's Avatar
    Join Date
    Oct 2003
    Location
    SoCal
    Posts
    5,587
    To your advantage?

    Possibly lower resale value (not original and “had some work done”).
    The bipolar electrolytic (blue) doesn’t appear to be bulging or oozing from the ends.
    Do you hear something wrong, perhaps in one speaker only, to suggest a problem?
    Do you have a way to measure cap values? Let alone at the crossover frequency range?
    Is there room and budget to replace the blue cap with something “better”?
    You -could- spend more time and money on crossover mods (e.g., charge-couple) than your purchase price.
    (I hope not ).

    Thought/opinion: I’d save money for less gooey woofers.

  5. #20
    Administrator Mr. Widget's Avatar
    Join Date
    Apr 2003
    Location
    San Francisco
    Posts
    10,667
    Mylar caps are pretty stable. (The yellow 4uF cap.) The coils and resistors are likely in as new condition, so only the NP electrolytic would even possibly need changing. As Grumpy said, making a change could lower your resale value. I probably wouldn't bother. Then again, swapping in a pair of Dayton film caps won't cost much and could only be better... audibly? Hard to say.

    https://www.parts-express.com/dayton...SABEgKwoPD_BwE


    Widget

  6. #21
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    The photo shows a before and after comparison. The woofer on the right hasn't been cleaned and the one on the left has. So the "gooey" is as taken care of as it's going to get. Kinda hard to see it in the photo, but there is a substantial difference and I'm satisfied with the result.
    I did measure the caps and they are 16.1 at each lead. Because they are still in the crossover circuit, they are in parallel (along with a 10 ohm resistor and 0.4mH coil, plus a 4 Ohm resistor and 1.6mH coil in series). The cap values are 4 and 12 microfarads (plus two .01 bypass caps), so 16.1 makes sense.
    The speakers sound great, so I'm not looking to correct a fault. However I have them open and would have no problem spending some money on them as they are good speakers and I'm a hobbyist.
    I know electrolytics degrade over time and these are over 30 years old. The blue cap is the 12 microfarad bypass cap for the woofer so not as critical as the yellow mylar in series with the 035TiA tweeter.
    Or I could just leave well enough alone and open a beer.

  7. #22
    Senior Member
    Join Date
    Feb 2019
    Location
    Germany
    Posts
    388
    Hi,

    the blue 12 µF 'lytic most probably is the bypass capacitor in the woofer's low pass filter. Lift one leg, measure it's capacity and it's ESR and leave it alone if both are in specs. Anyway, the polypropylene cap suggested by Mr. Widget isn't that pricey and hence won't hurt .

    Best regards!

  8. #23
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    Quote Originally Posted by Kay Pirinha View Post
    Hi,

    the blue 12 µF 'lytic most probably is the bypass capacitor in the woofer's low pass filter. Lift one leg, measure it's capacity and it's ESR and leave it alone if both are in specs. Anyway, the polypropylene cap suggested by Mr. Widget isn't that pricey and hence won't hurt .

    Best regards!
    All I have in the way of measurement equipment is a Fluke 89 IV multi meter. So I can't measure ESR. And yes, the blue cap is the woofer bypass cap. Being in Canada, the closest I can get to what Mr. Widget suggested is a 400 volt Solen PB for 6 bucks Canadian. Or about $4.75 USD. So pretty cheap.

  9. #24
    Senior Member grumpy's Avatar
    Join Date
    Oct 2003
    Location
    SoCal
    Posts
    5,587
    Quote Originally Posted by Cozmo View Post
    All I have in the way of measurement equipment is a Fluke 89 IV multi meter. So I can't measure ESR. And yes, the blue cap is the woofer bypass cap. Being in Canada, the closest I can get to what Mr. Widget suggested is a 400 volt Solen PB for 6 bucks Canadian. Or about $4.75 USD. So pretty cheap.
    If you just have the jones, do the mylar with a pair of 2x value Solens in series and put a dc bias between them ... 1M and 9v battery is easy... can look up recent JBL schematics to see how with a diode instead of the battery.

  10. #25
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    Quote Originally Posted by grumpy View Post
    If you just have the jones, do the mylar with a pair of 2x value Solens in series and put a dc bias between them ... 1M and 9v battery is easy... can look up recent JBL schematics to see how with a diode instead of the battery.
    Sorry Grumpy but that went right over my head. You'll have to dumb that down a tad.

  11. #26
    Senior Member grumpy's Avatar
    Join Date
    Oct 2003
    Location
    SoCal
    Posts
    5,587
    Four 8uF (if the mylar/yellow cap is now 4uF). Each mylar would get replaced by two caps (Solen is a manufacturer) of double the value. Wire them in series. So far, this sounds like an unreasonably expensive way to make a 4uF cap, but stay with me... The joint where the two meet and aren't connected to the board goes to a 1Mohm resistor (new) then the resistor's other end goes to the positive terminal of a 9v battery. The negative battery terminal goes to the black speaker terminal. This results in the same value capacitance where the mylar cap was (series cap values work like parallel resistance values) so no change in crossover frequency, but inserts a DC bias between the two caps. Supposed to sound better ... Just looked up some old references... perhaps use a 2.2 or 3 Mohm resistor instead... the battery might last longer.

    Some light reading:
    https://theartofsound.net/forum/show...led-Crossovers

  12. #27
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    If I were to replace the 4uF mylar in the tweeter circuit, I would most likely go with something more simple and long lasting it think. Just a decent quality film cap.
    The best I can do locally; replace both caps in both crossovers with 2 Solen 12uF 630V PPE for woofer bypass and 4 Clarity Caps (a 1.8uF Clarity Cap SA 630V in parallel with a 2.2uF of the same, times two) in series with the tweeter. $30.40 USD.

  13. #28
    Senior Member grumpy's Avatar
    Join Date
    Oct 2003
    Location
    SoCal
    Posts
    5,587
    Quote Originally Posted by Cozmo View Post
    If I were to replace the 4uF mylar in the tweeter circuit, I would most likely go with something more simple and long lasting it think. Just a decent quality film cap.
    The best I can do locally; replace both caps in both crossovers with 2 Solen 12uF 630V PPE for woofer bypass and 4 Clarity Caps (a 1.8uF Clarity Cap SA 630V in parallel with a 2.2uF of the same, times two) in series with the tweeter. $30.40 USD.
    Hmm, I think I’d just leave it alone, for that price and effort, but will be interesting to get your take on how it goes. Good to experiment and have fun!

  14. #29
    Member Cozmo's Avatar
    Join Date
    Nov 2013
    Location
    Ontario Canada
    Posts
    53
    I realize that the whole "upgrading crossover capacitors" thing can be viewed as a bit of a B.S. / snake oil type topic, and to the JBL purists on this site, might be seen as sort of sacrilegious to mess with a factory design. And, that the mylar cap is likely just fine, as would be the two 0.01uF bypass caps in parallel with both the mylar and electrolytic. But the electrolytic is now over 30 years old and it may be out of whack or eventually will be, or so I've read many times. So...since I'm in there messing around anyways, "why not upgrade the caps" is my attitude. These small bookshelves are quite remarkable and deserve to sound their best. I'm a hobbyist who doesn't mind spending a bit of time and money on something in order to see an improvement. It keeps me out of the poolhalls and off the street corners.

  15. #30
    Administrator Mr. Widget's Avatar
    Join Date
    Apr 2003
    Location
    San Francisco
    Posts
    10,667
    I don’t think that quality components are snake oil, though there is plenty of that going around, and I certainly don’t think terribly highly of most vintage JBL crossovers, but unless you get pleasure messing around with this stuff, I’d call it a day and enjoy them as they are.

    That said, you seem to enjoy messing about with them, so go for it.


    Widget

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Woofer surround question
    By ngccglp in forum Lansing Product Technical Help
    Replies: 11
    Last Post: 01-23-2013, 04:37 PM
  2. L20T3 Woofer Repair in NYC
    By FBooth in forum Lansing Product Technical Help
    Replies: 11
    Last Post: 12-11-2011, 08:46 PM
  3. 4430 Woofer Foam Surround Repair
    By D Of Oxford in forum Lansing Product Technical Help
    Replies: 2
    Last Post: 07-06-2009, 11:00 AM
  4. Quick woofer surround repair
    By Ochoa in forum Lansing Product General Information
    Replies: 9
    Last Post: 03-02-2007, 04:38 PM
  5. Woofer surround issue
    By Nightbrace in forum Lansing Product Technical Help
    Replies: 4
    Last Post: 01-28-2006, 10:20 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •