The Vintage JBL West Coast Sound becomes the…

[bwilkinson]

The parts list as well as where they can be purchased from are on page 4 of this thread, in a PDF. He also has supplied a layout that he used.

 

[Louie7]

Hi - I'm new. I'll be brief, as I plan to re-read this entire amazing thread again to get as much of it into my brain as possible.

My situation: A gift was made to me - a pair of JBL L88P speakers (aka 88 Plus) monitors. Grilles missing. Tweeters fried.

As most of you know, (but I'll state for the record), this is basically a two way version of the L-100 with cutouts for the M12 (midrange and L-pad) upgrade kit which magically(?) transforms the 88 Plus into an L-100.

I have purchased and will soon receive a pair of tweeters. At that point I will do my best to clean up the existing L-pad and possibly replace any capacitors.

... my long-range plan was to locate the mid-range speakers and either locate a used M12 L-pad or construct one to basically accomplish the 88 Plus to L-100 upgrade... (and yes, to install better speaker connectors)

But now, my whole concept has been turned around with the discovery of this incredible thread and the prospect of creating a 'better' crossover for all three drivers in the original cabinet.

What do you think ?

Suggestions ?

Thanks

 

[Swerd]

Hi - I'm new. I'll be brief, as I plan to re-read this entire amazing thread again to get as much of it into my brain as possible.

My situation: A gift was made to me - a pair of JBL L88P speakers (aka 88 Plus) monitors. Grilles missing. Tweeters fried.

As most of you know, (but I'll state for the record), this is basically a two way version of the L-100 with cutouts for the M12 (midrange and L-pad) upgrade kit which magically(?) transforms the 88 Plus into an L-100.

I have purchased and will soon receive a pair of tweeters. At that point I will do my best to clean up the existing L-pad and possibly replace any capacitors.

... my long-range plan was to locate the mid-range speakers and either locate a used M12 L-pad or construct one to basically accomplish the 88 Plus to L-100 upgrade... (and yes, to install better speaker connectors)

But now, my whole concept has been turned around with the discovery of this incredible thread and the prospect of creating a 'better' crossover for all three drivers in the original cabinet.

What do you think?

Welcome to the forum!

I think you'll be better off if you:

1. Build the new crossover - It will sound noticeably better than the original one.
   
2. Avoid using variable L-pads. Old and restored, or new, they oxidize easily, causing the sound to cut in and out.

Of course, all this depends on finding two midrange drivers at reasonable prices. Good luck .

 

[Louie7]

Thank you Swerd . . .

So, your design doesn't have any level controls for the sqwaukers and tweeters ?

I down-loaded your diagram and parts list, but I haven't had a chance to study them yet.

I presume it's just straight crossover at certain prescribed points with no pots at all.

My eBay LE25-2's arrived today. They 'appear' to be really dandy ( I realize that's not an audiophile term) and I'm going to measure and test them tonight before I post (eBay) feedback.

My immediate plan right now is to clean up the existing potentiometers and possibly replace amy caps, provided I have the correct ones on hand, and then install the tweeters and give the cabinets a trial run.

Next on the adjenda will be upgraded wire posts. The existing ones are wimpy; as you already know.

L7

 

[Swerd]

So, your design doesn't have any level controls for the sqwaukers and tweeters ?

I down-loaded your diagram and parts list, but I haven't had a chance to study them yet.

I presume it's just straight crossover at certain prescribed points with no pots at all.

The relative volume levels for the drivers are built into the crossover. In my opinion, no additional level controls are needed.

It might be nice to have variable level controls in speakers, but these variable L-pads always have a problem with oxidation. That's why you rarely see them in speakers. You have to trust the crossover designer to get the overall balance right.

My eBay LE25-2's arrived today. They 'appear' to be really dandy ( I realize that's not an audiophile term) and I'm going to measure and test them tonight before I post (eBay) feedback.

Dandy tweeter works for me .

 

[Louie7]

Those LE5-2's look really nice, and reports about them are glowing.
But I notice that all the subsequent LE5's, such as the -5, -8 and so on, are fitted with ceramic magnets.

I notice also that they are a fraction of the asking price.

How do they compare sound and performance wise ??

L7

 

[Swerd]

Those LE5-2's look really nice, and reports about them are glowing. But I notice that all the subsequent LE5's, such as the -5, -8 and so on, are fitted with ceramic magnets.

I notice also that they are a fraction of the asking price.

How do they compare sound and performance wise ??

The LE5-2 midrange that I have is hardly what I would call a smooth performer. Here is its raw frequency response curve.

The crossover had to do a lot to smooth that out.

If you get a different version of the LE5, it will very likely perform differently and probably will not work well with the crossover. Good crossovers are always custom made for the drivers being used. Substituting a different midrange driver will require a completely different crossover.

 

[Whitey80]

I know it's been quite a while since you were working on this, but I have some questions about it.

I recently picked up a pair of the 1st generation L100's (vertical alignment and a real crossover instead of basically L-pads as limiters, no boost on the pads, only cut, I might take a photo inside to show you what I mean)

Any ways, as it is, the mid seems to no actually put out midrange sound (very high in frequency, barely below what tweeter is doing, no voice comes from them, all from full range running 12" 123a. Not certain if this is how it is meant to be, or there is a problem with a crossover component.

Anyways, will likely be building a new one along the lone of yours or the Jantzen unit, but I believe the tweeter is a different driver in the first year of production that I have. Not a ton of info out there, as most people have the "a" models.

anyways, mostly just starting a dialog with you here, as I move forward with these.

 

[Swerd]

Any ways, as it is, the mid seems to no actually put out midrange sound (very high in frequency, barely below what tweeter is doing, no voice comes from them, all from full range running 12" 123a. Not certain if this is how it is meant to be, or there is a problem with a crossover component.

Anyways, will likely be building a new one along the lone of yours or the Jantzen unit, but I believe the tweeter is a different driver in the first year of production that I have. Not a ton of info out there, as most people have the "a" models.

You have what looks like a nice example of the original L100 Century from 1970. L100A models date from 1971-76, and another slightly different version of the L100A from 1977-79.

I found in my old files, a pdf copy of the Tech Sheet for the original L100 Century that you have. If you PM me with an email address, I can send it to you. It won't have enough info in it to help you design a new crossover, but you'll know everything that I know about them.

The tweeter in the L100 is a model LE20-1 (LE25 in the L100A). The woofer and midrange in the L100 have the same model numbers as in the L100A.

In the L100, the woofer runs full range, the midrange has a 2nd order high-pass filter (a cap and a coil) that rolls in at 2500 Hz but has no low-pass filter (upper frequency cut off), and the tweeter rolls in with a 2nd order high pass filter at 7500 Hz. In the L100A, the midrange and tweeter roll in at 1500 and 6000 Hz.

From the Tech sheets, the L100 and L100A have the same part numbers for the variable L pads.

If there is no sound coming from the midrange, my first guess would be that the variable L pad is corroded. Try a squirt of Caig Deoxit spray, and rapidly turn the knob back and forth several times. That may loosen some of the corrosion. Most of those old L pad potentiometers got hopelessly corroded.

As a guess, I'd suggest the woofer-to-midrange crossover from my rebuild should also work for you. But for the mid-to-tweeter, I really couldn't help.

 

[Whitey80]

Thanks for the info, I'll get a pic of the factory crossovers in these up soon, they are quite different from the A models, as I've said.
Apparently the mids work as they should. 2500hz seems so high for that driver, seems like they would be effective crossed over much lower.
PM'ing my email, would definitely like to see that tech sheet.

I will definitely be stealing your work, or the Jantzen.de stuff for the mid/woofer crossovers and on my own to work out the top end!

 

[STL.VOX.ROX]

JBL 88 Plus MODs

Just bought a pair of 88 Plus at a local thrift store for $15 each, and can't wait to do the L100 upgrade, as these speakers already sound AWESOME! My one question, which cabinet came with the 'waffle' foam face, the 88's or the 100's?

 

[Swerd]

The L100.

Do a google image search for JBL L100 and JBL L88 and you'll see plenty of examples.

 

[Swerd]

Thanks for the info, I'll get a pic of the factory crossovers in these up soon, they are quite different from the A models, as I've said.
Apparently the mids work as they should. 2500hz seems so high for that driver, seems like they would be effective crossed over much lower.
PM'ing my email, would definitely like to see that tech sheet.

I will definitely be stealing your work, or the Jantzen.de stuff for the mid/woofer crossovers and on my own to work out the top end!

In the new crossover, the woofer-to-mid crossover is about 950 Hz. That is pretty high for a 12" woofer, but the midrange didn't do well lower than that.

 

[Irvrobinson]

Yes, driver arrangement was a problem. I forgot to add part 6:

In this account I have repeatedly pointed out the problems caused by the driver layout of the L-100A. It has been a vivid lesson for me why almost all speakers today keep the drivers arranged in a vertical line. This photo (borrowed from a highly informative website on the history of James B. Lansing, his companies, and his speaker products: L100/4310) shows the four different layouts of the various JBL studio monitors made in the '70s.

The redesigned crossover I’ve described is designed specifically for the L-100A model (2nd from left). The L-100 model (3rd from the left) appears to have its drivers arranged in a vertical line. That might be a more desirable used model to buy if you can find one, but the redesigned L-100A crossover may not work as well for any of the other models.

And would the driver arrangement of the JBL LSR6332 cause similar issues? If not, why is the LSR6332 different?

 

[STL.VOX.ROX]

The L100.

Do a google image search for JBL L100 and JBL L88 and you'll see plenty of examples.

That is why I asked "The Guru". All of the 88 Plus images I found showed the flat colored grilles, but the pair I have [which are definitely 88's as they do not have the mid-range 5", and DO have the cover plate] have the 'waffle'-style grille. Thank you MUCH for sharing your knowledge and this information so that this already very good speaker may attain sonic greatness!

 

[Swerd]

And would the driver arrangement of the JBL LSR6332 cause similar issues? If not, why is the LSR6332 different?

I redo a crossover for speakers I bought in 1973, and now I'm the resident JBL expert . Well not really, but I can always speculate .

I had to look up the LSR6332 to see what it is. Although it and the L100A are both large boxy 3-ways, I doubt if there is much similarity between them. The tools for crossover design have changed significantly since those distant days. The drivers are almost certain to be very different. I hope the midrange is smoother that that of the L100. And JBL is not at all the same company today as it was in the 1970s.

The LSR6332 has its 3 drivers arranged in a vertical array, if the cabinet sits vertically on its narrow end as pictured. I read on the link that the midrange/high frequency sub-assembly may be rotated 90° for horizontal or vertical orientation. See the illustration on page 4 of the spec sheet. The frequency response curves on pp 2-4 look good, but they don't seem to show it measured both vertical and horizontal.

Most people who had L100s in the 1970s kept them horizontally, on their long sides. Way back when, I kept mine that way, but by the early 90s, I sat them vertically on stands. I once heard someone say that the L100 had its drivers arranged that way so it wouldn't matter whether they sat vertical or horizontal, they would sound similar. I don't know if that was true or not, but it sounded like a clever idea at the time.

So it does seem that both speakers had similar marketing goals. I suspect the modern speaker may do a better job, but I certainly have not heard it.

 

[Swerd]

All of the 88 Plus images I found showed the flat colored grilles, but the pair I have [which are definitely 88's as they do not have the mid-range 5", and DO have the cover plate] have the 'waffle'-style grille. Thank you MUCH for sharing your knowledge and this information so that this already very good speaker may attain sonic greatness!

Interesting. Maybe a previous owner bought L100 grilles for them.

The foam in my waffle grilles crumbled a long time ago. At the time JBL sold a cloth replacement kit, which I got.

Good luck with your rebuild project. Get some photos, and show them here.

 

[Irvrobinson]

I redo a crossover for speakers I bought in 1973, and now I'm the resident JBL expert . Well not really, but I can always speculate .

I had to look up the LSR6332 to see what it is. Although it and the L100A are both large boxy 3-ways, I doubt if there is much similarity between them. The tools for crossover design have changed significantly since those distant days. The drivers are almost certain to be very different. I hope the midrange is smoother that that of the L100. And JBL is not at all the same company today as it was in the 1970s.

The LSR6332 has its 3 drivers arranged in a vertical array, if the cabinet sits vertically on its narrow end as pictured. I read on the link that the midrange/high frequency sub-assembly may be rotated 90° for horizontal or vertical orientation. See the illustration on page 4 of the spec sheet. The frequency response curves on pp 2-4 look good, but they don't seem to show it measured both vertical and horizontal.

Most people who had L100s in the 1970s kept them horizontally, on their long sides. Way back when, I kept mine that way, but by the early 90s, I sat them vertically on stands. I once heard someone say that the L100 had its drivers arranged that way so it wouldn't matter whether they sat vertical or horizontal, they would sound similar. I don't know if that was true or not, but it sounded like a clever idea at the time.

So it does seem that both speakers had similar marketing goals. I suspect the modern speaker may do a better job, but I certainly have not heard it.

To be perfectly honest, I was only asking because GranteedEV and I were having a discussion in another thread about whether or not the 6332 would sound similar to the Revel Salon 2, and I randomly happened upon this thread that disses a speaker that grouped drivers similarly, the fact that they were both JBLs is a coincidence, and I figured this thread might give me some standing to continue the argument. Frankly, the issue isn't that critical.

 

[leesonic]

I recently picked up a pair of the 1st generation L100's (vertical alignment and a real crossover instead of basically L-pads as limiters, no boost on the pads, only cut, I might take a photo inside to show you what I mean)

Any ways, as it is, the mid seems to no actually put out midrange sound (very high in frequency, barely below what tweeter is doing, no voice comes from them, all from full range running 12" 123a. Not certain if this is how it is meant to be, or there is a problem with a crossover component

Please do take a picture of your crossovers. As I probably mentioned, mine had just a cap in series with both the mid and tweeter, there were no inductors as mentioned elsewhere. If you look at the schematic of my modified crossover, you'll see these two caps in the "original" part of the circuit. What I did with mine was wire the L-pads in with these, since the Murphy design crossover made no mention of using them.

Maybe your midrange is damaged in some way? You won't do it any harm if you remove it and connect it directly to your amp, but only use limited volume obviously.

Lee.

 

[Whitey80]

Maybe your midrange is damaged in some way? You won't do it any harm if you remove it and connect it directly to your amp, but only use limited volume obviously.

Lee.

Believe me, that was the first thing I did, within minutes of hooking them up for the first time! The drivers are fine. Swerd says they roll in at 2500hz, which, if he's right, sounds about like that, so high in frequency for a mid to be picking up, but oh well.

Anyways here's a photo of the crossover from the earlier L100