JBL L19A Questions

The Dayton stuff is surprisingly good...I'd save the high quality stuff and the $$ spent on them for better speakers (like Magnepans for instance which really respond well to xover rebuilds).

Peete.

Quote:

Originally Posted by _Spanky_ 

Alright. I've also seen ClarityCaps for about the same price as Dayton. These are actually my best speakers so far (currently using the Best Buy $60-wonder Insignia bookshelf speakers) so I wanna get them fixed up as I'll be using them for quite a while. What about the ratings? The original schematic calls for 7uF and 18uF but I can only find 6.8uF and 20uF for the Daytons and 6.8uF and 18uF for the ClarityCaps. Is that a problem or is it ok?

Yep it's a problem...you need to find exact value (uf and V ratings) replacements...however you can use electrical theory to your advantage when selecting caps....for instance (IIRC) if you wire a cap in series it halves the value of it ( like 2 x 100uf caps in series become 50uf ) Parallel wring for the same 100uf pair would result in 200uf in total but raise the V ratings to double the stated amount (on the cap body). If you cannot source a 7uf cap look for something that adds up to that total (using series or parallel wiring scheme) to arrive at the target values. Remember to match V rating (or go above it which is fine). In your series or parallel wired caps the cap with the lowest voltage rating takes precedence.

What caps are you looking at  (besides Dayton and Clarity) ?...I may be able to suggest possible combinations for you to order that will work.

Are you sure the 18uf/7uf caps are non polarized (meaning electrolytic types which have a + and - pole rather than film types which have no polarity) ? If I had to guess I'd be willing to bet that 18uf cap is polarized in which case finding such a value should be very easy.

Could you post the xover schematic for your speakers please or let me know the exact model number of them ?

This combo would work for the 7uf value...clarity cap 4uf 250V + 3 uf 250V = 7uf 250V wired in parallel. The 18uf cap has an exact value replacement in the Clarity line....just double check that that 18uf cap (or even the 7uf one) are actually film caps and not electrolytic types.

Peete.

Quote:

Originally Posted by _Spanky_ 

Good thing I haven't gotten caps yet then :) 6.8uF isn't close enough to 7uF? The 18 to 20 I can understand. As for brand of caps, I'm not really looking at anything specific. I did look up some vishay on eBay but they only had one of the ones I needed. The Dayton caps will be about $40 shipped, I think if cost stayed under $50, I would be pretty pleased. I did test one speaker before redoing the surrounds (it had all of the surround still on it and I only used low volume) and it worked great. Do I absolutely need to recap?

 

I do have the schematic:

http://dl.dropbox.com/u/464376/L19%20ts.pdf

 

I really hope they are non-polarized :) I've recapped several PCB's that use electrolytic caps with the stripe so those are easy. On the crossover, I have no idea what's + or -. What are the minimum V ratings for caps in a crossover circuit?

 

Looking at ClarityCaps, I could go 6uF and 1uF in parallel, wouldn't raise the cost very much.

Judging by that schematic it looks as though that 18uf cap may be non polarized (but an electrolytic type). Is there any way you can post a pic of the xover parts themselves....have a close look at the 18uf cap and note all printing on it. I would suggest replacing the cement resistors with Mills wire wound non inductive types (12 W) and use HQ caps to replace the 18 and 7 uf sizes. If you change the value it changes the xover point and may effect phase response.....it's best to try and match the exact values (which isn't that difficult to accomplish with parallel wiring of 2 or more parts to arrive at those specific values). V rating of 250V is plenty...I bet the 18uf cap is 50 or 100V (maybe more but I can't say without seeing the actual part). If you want to further improve the xovers replacing the cheap stock inductors with Erse Copper Foil (16 awg in .4mh and 1.2 mh values which is exact match with your L19 xover) would complete the rebuild. You could use much cheaper Janzen Air core (from Partsexpress) inductors but the copper foil types are not that expensive and perform superbly (in concert with Mills resistors and HQ caps). I bet the old JBL's would be totally reborn with such an upgrade ...I'm fairly confident if you go the last mile with the rebuild you'll be scraping your jaw from the carpet floor after the first listen.

Peete.

Sounds like a good start spanky....yeah keeping the VC centered when replacing the surround is a tough one. You may need to do that whole process over. Another option is replacing the drivers with the Dayton Classic II woofers...they are supposed to be really good drop in replacements for old JBL's but that's a fairly costly upgrade (although a lot less $$ than buying drivers from JBL mind you).

As far as the inductors even the cheaper 18 awg Jantzen Air core would be a major improvement over the old stock units. That pic I can't quite make out the writing on it. It looks like (18uf) an axial lead NP (non polar) electrolytic. The paper film cap is likely drifted and dried up (along with the axial 18uf). The rebuild of your xo should really bring the JBL's back to life (once you have the VC issue sorted).

Keep us updated ......I have a set of LX44's that need some attention of a similar sort although the surrounds are still good as new. The xover sure could use an upgrade after gawking at it over this past weekend (out of curiosity).

Peete.

Nope, stick with 18uf...I'm fairly confident that the 18uf cap is non polarized but double check it to be sure (you should see a + symbol or a black stripe down one side if it is polarized). Double check that cap is my advice so no parts ordering mistakes are made.The film cap (7uf) is definitely not polarized. Indeed install direction does not matter with non polarized parts

Peete.

Well you could change the value to 16uf but you may not like the result...then again you might. My gut feeling is to stick with the stock value FWIW.

Peete.

Quote:

Originally Posted by _Spanky_ 

I'm thinking that since the 4301B is the professional/studio model that the 16.5uF cap might give a more level frequency response over the 18uF that the L19A (home model) has. If it does terrible stuff, I can always get some more 1.5uF caps of the same brand and raise it to the original 18uF.

That you could....give it a try...I would order the extra 2 x 1.5uf caps when you put the order in for the other parts (so you don't have to pay for shipping twice). I'm sure you could use those caps elsewhere if the 16.5uf sizes float your aural boat

Peete.