L88P question

[JBLRaiser]

Without the kit, can I still convert the two ways to three ways and how? If not. are kits still available? Thanks

[GordonW]

It is possible; what's required is an LE5-2 midrange, and someone who can custom-make you the "helper crossover" unit to convert the electrical network for 3-way mode...

I'm about to be performing this exact job, for a client of mine. Once it's done, I'll have more exact procedures on-hand about what's required to perform the entire job...

Regards,
Gordon.

[GordonW]

Just completed the change-over.

Parts list, for L88P "Plus 12" conversion (to L100 spec):

- one pair, LE5 type midranges (the client here used LE5-5s; LE5-2s are the original ones for this setup. LE5-5s, 2105Hs, LE5-9s or LE5-11s can be used, if necessary, with minimal sonic difference, in the end)

- one pair, 3uf mylar or polypropylene caps

- one pair, 8 ohm 30-50 watt L-pads (make sure they're NOT more than 2" in diameter, or they WILL NOT FIT).

- Two feet each, black, red and white, 18g wire

- two 1/2 inch length, 20 or 22g solid core wire leads (the cut-off ends, as long as they're 1/2" long each, from the 3uf cap leads, will work).

- a small length of rope caulk or automotive strip caulk

- if using LE5-5, LE5-9 or other midranges with the "faston" (flat blade plug terminals), two each, male and female 1/4" wide faston "spade" terminals, either crimp or solder-on type, for 18g wire (blue or red crimp terminal sleeves).

Procedure:

Disassemble the L88- remove the woofer, the blanking plate where the mid will go, and the foilcal (use a hot heat gun to soften the adhesive, at which point you should be able to EASILY peel off the decal. If it's difficult, use slightly more heat until it becomes easy to remove). Once you remove the foilcal, you should see an empty 3/4" hole, where the midrange L-pad shaft will go into, once it's installed.

Once the foilcal is removed, remove the four screws, holding in the blanking plate where the midrange L-pad will go. Remove the blanking plate, from the inside of the cabinet.

With an electric drill, drill a 5/16" hole in the center of the black paint "dot" (where the front panel paint "oversprayed" onto the blanking plate through the midrange L-pad hole) on the L-pad blanking plate. Bolt the new 30 watt L-pad in, through this new hole, where the knob side of the L-pad is on the painted (front) side of the plate. Before tightening the L-pad nuts, MAKE SURE the leads out of the L-pad will be facing DOWN (toward the woofer) when the blanker plate/L-pad assembly is bolted back into the cabinet. Depending on the L-pad, you may need to space the L-pad rearward (using either washers, or the second "jam" nut supplied with many L-pads) to space the L-pad so that only about 1/4" of threads are sticking out through the front of the blanking plate, before the top nut is installed.

Drill an approximately (it's not critical, as long as two 18g wires can pass through the resultant hole) 1/4" hole in the side or rear of the midrange enclosure, on the side nearest the L-pads, to allow wire passage into the mid enclosure.

Here's where it gets a little sneaky... but it's simple: Unplug the 4-pin plug-in connector (with the red and black wire) from the back of the factory crossover. Unclip and slide back the white cap from the 4-pin connector. Unsolder the RED wire from pin 2 of the inside of the connector, and slide the red wire out of the connector cap (we will be re-connecting it elsewhere, later).

Take the 1/2" long piece of solid core, and bend a "u" shape, so that it can bridge across pins 2 and 4 (diagonally opposed) in the connector. Slip the wire into the pins (2 and 4) and solder into place.

Take our new red 18g wire from the parts list above at the top, and cut about a 1 foot length. Slip the wire into the cap of the connector, to REPLACE the red wire we just removed. Strip and solder this red wire, into pin 3 (the only un-occupied pin at this point) of the connector.

Strip the other end of this new red wire. Take the 3uf cap, and solder one of the two red wires (the old and the new) to either end of the cap, so that the cap is in-line between the two red wires. Glue or otherwise mount the 3uf cap to either the rear of the cabinet near the original crossover, or to the masonite board of the orginal crossover, just above the original crossover (when the cabinet is sitting normally, as it will be used in service).

Un-wrap the previously un-used white and black leads coming from the factory L88 crossover. Cut off one foot each, of the new white and black wires, and strip both ends of both of them. Solder BOTH black leads (the new one and the previously unused one from the L88 crossover) to pin 1 of the L-pad. Solder the new white wire to pin 2 of the L-pad. Solder the previously unused white wire from the L88 crossover, to pin 3 of the L-pad.

Run the other ends of the new white and black wires, inside the cabinet, through the hole previously drilled in the midrange enclosure, so that the wires are run to the back of where the new midrange will go. Use the rope caulk or automotive strip caulk to putty in around where the new wires go through the wall of the midrange enclosure, in order to prevent air leaks from the main part of the box and the mid enclosure.

Most L88 speakers will have a small square of yellow fiberglass damping material, in the mid enclosure already. If they don't, you should "borrow" a small square (big enough to cover the rear wall of the mid enclosure) from somewhere in the main enclosure (near the top, around the tweeter, should be best), and place it in the back of the mid enclosure, loosely pressed against the back wall of the can.

Plug or otherwise connect (crimp or solder on the connectors as required if using a mid with faston connectors, using the MALE crimp/solder terminal on the WHITE wire, and the FEMALE crimp/solder connector on the BLACK wire), and bolt in the midrange, using the screws that previously held on the midrange chamber blanking plate.

Reach into the cabinet, where you can get to the terminals of the TWEETER L-pad (red and black wires, existing stuff). Bend these terminals AWAY from the front baffle, so that they are closer to the body of the L-pad (ie, they're no longer sticking straight out sideways from the L-pad, but instead "hug" the L-pad body). Then, using the original screws, bolt the midrange L-pad/blanking plate back into place.

Plug the woofer back in (remember, green goes to red, black to black), bolt the woofer in. You're done... time to repeat the procedure on the other speaker cabinet!

Once both speakers are done, fire both speakers up on an amp at moderate volume, and make sure all the drivers are playing. Once this is determined to be so, adjust mid and tweeter L-pad levels to taste. The levels will almost undoubtedly wind up different from the original tweeter level, so don't sweat it. The LE5 will help out, so slightly less tweeter level will usually be required than originally...

On the cosmetic front- you can aquire some of the L-pad knobs, from pretty much any JBL crossover of the era, to put on the new midrange L-pad shafts. Also, I have determined that L100 foilcals WILL fit the front panel and the L88 L-pad hole spacing...


NOTE: Please, if you see an obvious error in the procedure (doesn't make sense, etc) post here... I typed this from memory, of about an hour ago. I think I've got all the steps...

Regards,
Gordon.

[4313B]

Thanks Gordon!

LE5H too but they are the most rare on your list. I did see a pair not long ago on eBay though.

[JBLRaiser]

Thank you GordonW for taking the time to answer my question. Very useful quality information. I'm south of you about 75 miles . I have a brother and three sisters in Atlanta. One day when I'm up, I'd like to see your shop/store. William

[JBLRaiser]

As a follow up at the risk of exposing my lack of technical knowledge, would a L100 crossover fit in place of the L88 xover with screw holes added ..............'Laziness is the mother of invention':homer:

[GordonW]

Needs to be an L100A crossover (to work correctly with the drivers in the L88P)... but I THINK it will work. Can't guarantee about the clearance between the side of the cabinet wall, and the edge of the crossover board... but the L-pad spacing is the same.

But, once you have to re-make the rear input panel (the L88 crossover is made onto the jack plate) for the new crossover wiring, it'll probably take just as much time as my procedure above, to install L100A crossovers... AND it'll cost more money (L-pads and 3uf caps are CHEAP, compared to complete L100A crossover networks)...

Regards,
Gordon.

[billyboyJBL]

jblraiser,my thoughts to you are to get a pair of le5-5s or le5-2s ,drive them up to gordon ,and let him work his magic on them like he did mine. you will not regret it ,the man knows his stuff:applaud:. i am enjoying tower of power on mine right now,thanks again gordon!!!!!!

[epoch5]

Would LE5-8s work ok for this?

[Zilch]

http://audioheritage.org/vbulletin/showthread.php?t=5706

[epoch5]

Thanks I think I get it.

[Thom]

of all the JBL's out there the LE5 is not that special and not that efficient. An awful lot of the time if you get the urge to mix and match it's the efficiency that kills you. (why hook it up if you won't be able to here it). Some of you are going to scream about messing with what god I mean JBL put together. Thats a valid point of view, just make sure your not one who occassionally has an improvement on JBL. It's sacred or it's not.

[tbcyberzom]

Hi..it been a while..i found this jbl l88p in the garage sale for 10 bucks..the condition is not so nice but the drivers work beside a lot of stains and push in tweeters..i took them a part and clean everything and spray the pots and add a new speaker post because the original is brokens..i took the mindrange cover and i saw two wires black and white and i have a two midrange l5-2 and i hook them to the midrange wire (black and white) and i power up the speakers and the midrage doesnt work? so my question is ..why the wires are already in place ? is this supposed to be part of the upgrade?

[Robh3606]

You need the complete expander kit for it to work. It's all in the Library and the schemetics are on the Forum under consumer links. Read post 3 in this thread.

Rob:)

[tbcyberzom]

i got it figure out.now where do i get the proper L-PADS..please advise

[planetzany]

Hello all,

Would anyone know of a reputable speaker modification outlet for vintage speakers in West London (UK)?
Any advice would be great, thanks.