The Vintage JBL West Coast Sound becomes the…

[bwilkinson]

Schematic

Be careful of what you plan on doing there. If you look through the thread more, you will realize that you don't necessarily connect the positive out to the positive terminal with Dennis Murphy's crossover design. I am assuming that your drivers are the same as mine (not necessarily true, as I understand that JBL did change the drivers in their later L100A). In mine, I connected the positive out to the red terminal of the woofer, positive output of the midrange to the black terminal of the mid driver, and positive output of the high to the positive terminal of the tweeter.

The reason behind this is this - all the drivers are in phase in Dennis Murphy's design. As Swerd stated, test your drivers with a 1.5V battery. If the driver pushes outward with the positive end of the battery connected to that terminal, then that terminal is now "positive". JBL wired the speakers out of phase. If you connected a 1.5V battery to the red terminal on the back of the speaker, the woofer would push out, the midrange would push in, and the tweeter would push out. So not only would you need to swap between the Dennis Murphy electronics and the JBL electronics, but you would also need to reverse the polarity of the midrange.

 

[leesonic]

All 3 should have their true positive terminals (as determined by the battery test) wired to the positive side of the board, and their true negative terminals should be wired to the minus or ground side of the board.

I was thinking of putting three toggle switches on the terminal plate, so you can switch between the "west coast sound" (JBL) and "coast to coast sound" (Murphy). Think this is a good idea? Maybe even a switch to reverse the polarity of the midrange to get the authentic JBL sound?

I understand the original crossover had the midrange wired out of phase with regards the other drivers. That's why I mentioned before about having a switch to reverse to polarity of it. It would be easy to do, just a DPDT switch with the four corner terminals connected together in an X shape. The input would connect to either the top or the bottom of the X, and the driver would connect across the center two terminals.

 

[Swerd]

JBL apparently wired the polarity of some drivers differently over time. So the drivers you have might be different than mine were. Before you do anything, do the battery test with your speakers, and note which wires from the original crossover were attached to which terminals for all three drivers.

Once you know which terminal is positive on each driver, wire each driver as shown in the Murphy schematic diagram.

 

[bobbybluz]

JBL L-100's



I found this thread and now I want to try updating the L-100's I got for free several years ago. The cabinets have some battle scars and the front covers disintegrated a few decades ago but the drivers are in perfect condition. I don't have a problems with amps to drive them since I have a collection of vintage BGW's that can drive anything. I think a 250C will work just fine without much risk of damaging drivers.
I want to update the crossovers along with changing the inputs to binding posts for Pomona connectors.

 

[bwilkinson]

I found this thread and now I want to try updating the L-100's I got for free several years ago. The cabinets have some battle scars and the front covers disintegrated a few decades ago but the drivers are in perfect condition. I don't have a problems with amps to drive them since I have a collection of vintage BGW's that can drive anything. I think a 250C will work just fine without much risk of damaging drivers.
I want to update the crossovers along with changing the inputs to binding posts for Pomona connectors.

You will not be sorry you did - they are now incredible sounding speakers.

 

[zildjian]

I've been reading this thread since shortly after it was created, and it's still on my To-Do list to take my L-100's and start this project. They are still connected to the same Marantz 2275 receiver that has powered them since the mid 1970's. I know it will sound silly to say this, but even when the sound is improved with new crossovers, a small part of me will miss the sound they used to have if it changes much. These are the speakers I grew up with and first fired my love of audio equipment.
-Brad

 

[leesonic]

I've been doing some work on my L100s recently. The first problem I found was one of the woofers would make a scraping sound if you tapped the cone ("don't tap it then" should be the answer). It seemed to work OK playing music, but I didn't want it to become a problem later on, so I took the woofer out. Well, that was the plan, but the woofer wouldn't come out at first, so I removed the midrange and tweeter to see if I could get access to the back. I managed to squeeze my hand through the tweeter hole and eventually get the woofer out by pushing on the frame edge with my fingers. It turns out the voice coil had become detached from the spider. What makes these woofers great is you can remove the magnet to make repairs, and once I got the magnet off, I found a date stamp inside of September 18 1974.

After removing the dust cap, I re-attached the voice coil to the spider using some black glue purchased from Orange County Speaker. After some trial and error, I found a piece of glossy cardboard that was part of a magazine cover to use as a shim between the coil and the magnet pole. Since the spider wasn't in contact with the coil like it should be, once I got the glue around the edge of the coil, I used a coffee mug to push down on the cone, which brought the coil back in contact with the spider. Once this was done, and given a few days to dry, I tested the woofer using some music with long, low bass sweeps, and it seems to work perfectly! I reattached the dust cap using the same glue, and then gave it a couple of coats of black "Wet Look" speaker paint from Parts Express. Looks good doesn't it?

I then turned my attention to the crossover. I wanted to be able to switch back to the original spec crossover if I need to, so I modified the design to include three switches to switch between the Murphy and JBL spec crossovers. I was looking at Parts Express, and they stock a heavy duty 4 pole Double Throw switch that I could use for the mid, and use two DPDT switches for the woofer and tweeter. Two of the poles on the midrange switch would be to switch between crossovers, the other would be to reverse the polarity when using the JBL crossover. I could have used a 6 pole switch for everything, but finding one with a high current rating was a problem. Not that I planned on doing this, but you could in theory listen to the speaker with the JBL crossover on the woofer, and the Murphy crossover on the midrange and tweeter, or any other combination. Here you can see my modified schematic. It doesn't include the L-pads, but these will be used on the JBL crossover section.

Using parts from Parts Express and Erse Audio, I was able to build my crossovers. I did try using a big 5x9" circuit board from Parts Express, but it proved too small, it was mainly the big 25w resistors I was using. So I used a piece of scrap hardwood I had lying around the house, and hard-wire everything on the back. My next plan is to remake the JBL crossovers with some new capacitors and L-pads. I will then mount a 5x7" dished plate on the back of the speaker cabinet which will hold some chunky binding posts, and the three switches to switch between crossovers.

Watch this space for more updates...

 

[leesonic]

Got to spend some more time working on the JBL L100 restoration and upgrade.

Here is a picture of my "re-manufactured" factory spec crossovers. Since the Parts Express L-pads have a longer shaft than the stock crossovers, I cut a new piece of 1/2" MDF and mounted them on there.

And here are the new terminal plates I made, again using parts from Parts Express. The middle switch is the 4-pole double throw for the midrange, I'm going to wire two poles to switch between the Murphy crossover and the JBL spec crossover, and the other two poles to switch the polarity of the midrange driver, just like JBL did.

 

[Swerd]

Looking good Lee. Nice work and nice photos. Thanks! It looks like it won't be long before you install all your new work and get to listen.

I'm looking forward to your impressions of the comparison.

 

[leesonic]

I got one midrange switch wired up today, not mounted on the plate (see above) only another five to go. I did this first since they sit between the woofer and tweeter switches, and won't be as easy to get to when they're all together. I couldn't wait, I had to hear what the difference was, so I connected it up with wires twisted here and there.

What I can tell you is the difference between the Murphy crossover and the JBL is staggering. With the JBL, it sounds like the midrange is the tweeter as well, there is FAR too much treble getting to it. I've just posted a request on a Freecycle web site I'm on for a microphone. If I can get hold of one, I'll post a video up on YouTube of the differences between the two crossovers.

 

[Swerd]

What I can tell you is the difference between the Murphy crossover and the JBL is staggering. With the JBL, it sounds like the midrange is the tweeter as well, there is FAR too much treble getting to it.

With that original crossover JBL used, there was no low-pass filter for the midrange driver, letting it go way too high. And that driver's frequency response is not very smooth. The new crossover limits the midrange driver upper end to 5 kHz with 4th order roll-off slope.

 

[leesonic]

Here is another update on my L100 project...

I mounted the new upgraded Murphy crossover board to the back panel, drilling the top holes with a Milwaukee 1/4 in right angle adapter I got from Home Depot (part number 48-32-2100) with a Craftsman drill bit with a 1/4 hex shank. I used some strips of foam insulation behind the board to stop it vibrating. You can see the new JBL spec crossover L-pads in the top of the picture, this was mounting using the orignal screw holes in the baffle (for the moment, I might fill these when I refinish the cabinets).

Here is a close-up of the terminal and switch plate. I tried to run every common or ground wire back to the negative terminal in a kind of star-earth way, that's why there are so many wires : 2 to the JBL spec crossovers, 3 to the Murphy crossover, 2 to the woofer and tweeter, 1 to the midrange switch.

I also replaced the old fibreglass insulation with some new acoustic wadding or cabinet damping.

Here is a view of the back panel, looks more business like now doesn't it?

And here they are fully assembled. I had to pull out one of the tweeter domes with a pin, so I sealed it using some "Wet Look" speaker paint from Parts Express. I did the woofer caps as well, since I had to remove one.

Before everything was buttoned up, I was able to play each driver on it's own, just to make sure I wired the switches the correct way. This revealed some interesting results...

The woofer reproduces a lot more midrange frequencies using the JBL crossover, these are rolled off with the Murphy. From the factory, it has no crossover components of any kind, relying on it's natural roll-off. Likewise, the tweeter reproduces more midrange frequencies with the JBL crossover than the Murphy. I hate to point the finger at the little guy in the middle, but I've already mentioned the midrange reproduces a lot more treble than it should in JBL crossover mode. What is also interesting is it seems to get more low frequencies as well. This was noticed using nothing more high tech than some dust that just happened to be sitting on the cone. With just this driver connected (hence no vibration from the woofer), switching from Murphy to JBL caused the dust to bounce off the cone. Actually, the speaker doesn't sound all that bad with just the woofer and tweeter connected using the JBL crossover, in a loudness button "boom and tizz" kind of way, less midrange.

Connecting all the drivers and placing them back in the cabinet, it is easy to hear the difference when switching crossovers. Going from high to low, and with the switches set to the Murphy crossover, here's what happens. Switching the tweeter over from the Murphy to the JBL crossover, now there's more midrange. Switching the midrange now there's more midrange and even more treble, switching the woofer over adds even more midrange.

It's easy to see why this speaker is impressive when you first hear it, there's so much attack because all three drivers are having a go.

What's weird is the midrange interaction with the woofer. I don't know what you call it, but we all know the sound a pair of out-of-phase speakers make. That weird sound like it's coming from behind you, or inside your head, it's kind of hard to describe. I've been to peoples houses (who should know better) and told them one of their speakers is wired back to front. Of course they deny it, then when they check, it is. I've been to HiFi shops, record shops, heard car systems, and can easily tell when a speaker is wired up wrong. Well, I had each of these L100s lying on their backs on the floor with a piece of wood propping them up so I could switch between crossovers. Switching from the Murphy to the JBL crossover on the midrange, with the woofer set on the JBL crossover, sure enough you can hear the fact that the midrange is wired out-of-phase. This obviously isn't helped by the fact that they have such an overlap. This doesn't happen using the Murphy crossover.

These are just initial observations, I need to get them set up properly and get down to some serious listening...

 

[zildjian]

Great work Lee. Looks awesome. Can I send you my L-100's???
I really appreciate you sharing the sonic differences you heard in switching back and forth between the two crossovers. I listed to the L100's for so many years that I know their original sound well. I want to replace the crossovers some day when things calm down and I have time to more time to mess with it, and I think it would be neat to switch back and forth for nostalgia sake since they were my first "hi fi" stereo speakers, so I might copy your switching design if it's OK with you.
-Brad

 

[leesonic]

Great work Lee. Looks awesome. Can I send you my L-100's???

Well, I could make you a set of crossovers and plates like mine...

I really appreciate you sharing the sonic differences you heard in switching back and forth between the two crossovers. I listed to the L100's for so many years that I know their original sound well.

As I said before, they have a very interesting sound the way they are. Maybe it's right, maybe it's wrong, but they certainly hit hard. I wanted to be able to switch back to the original (albeit restored) crossover design. The cost of making new crossovers to the original spec cost a lot less than the Murphy design, and I sold my original crossovers to finance. A couple of caps and a couple of L-pads on a piece of wood, not complicated.

I want to replace the crossovers some day when things calm down and I have time to more time to mess with it, and I think it would be neat to switch back and forth for nostalgia sake since they were my first "hi fi" stereo speakers, so I might copy your switching design if it's OK with you.

Be my guest.

 

[Swerd]

Lee - Thanks for all the new photos.

When I did new Murphy crossovers for my L100s several years ago, I noticed in addition to the overall improved sound, that the new crossovers resulted in less volume. If I had to guess, it was roughly 3 dB less, but that was only an estimate. With your switches, is it possible for you to measure the relative difference in volume? I would appreciate knowing what you find.

When you do some more listening, try and find some music that excites the large 6-7 kHz peak with the original JBL crossovers. You'll recognize it because it sounds prominent and ugly. If I remember, trumpets playing high notes can do it, but so can other instruments. It was caused either by breakup of the midrange driver, or by strange diffraction artifacts because the midrange and tweeter are working together. Compare how it sounds going back and forth.

What's weird is the midrange interaction with the woofer. I don't know what you call it, but we all know the sound a pair of out-of-phase speakers make. That weird sound like it's coming from behind you, or inside your head, it's kind of hard to describe. I've been to peoples houses (who should know better) and told them one of their speakers is wired back to front. Of course they deny it, then when they check, it is. I've been to HiFi shops, record shops, heard car systems, and can easily tell when a speaker is wired up wrong. Well, I had each of these L100s lying on their backs on the floor with a piece of wood propping them up so I could switch between crossovers. Switching from the Murphy to the JBL crossover on the midrange, with the woofer set on the JBL crossover, sure enough you can hear the fact that the midrange is wired out-of-phase. This obviously isn't helped by the fact that they have such an overlap. This doesn't happen using the Murphy crossover.

This raises a question. The original crossover from my JBLs did wire all 3 drivers in phase with each other.

The problem was that some, but not all JBL drivers, made in the 1970s did not follow what later became an industry standard of using the red terminal as positive and the black terminal as negative. That's why I recommended using AA batteries to test the polarity of each driver. Some drivers were built with the black terminal as the positive, but that varied over the years. It has caused great confusion now that people are accustomed to the standard red = positive.

Are you sure your speakers came with the midrange driver wired out of phase with the woofer and tweeter? Or did it seem that way because of their non-standard color coding? It just might be possible that your speakers were mistakenly wired out of phase when they were built.

 

[leesonic]

Lee - Thanks for all the new photos.

You're welcome.

When I did new Murphy crossovers for my L100s several years ago, I noticed in addition to the overall improved sound, that the new crossovers resulted in less volume. If I had to guess, it was roughly 3 dB less, but that was only an estimate. With your switches, is it possible for you to measure the relative difference in volume? I would appreciate knowing what you find.

Wish I could help you there. I tried placing a "wanted" ad on a local FreeCycle board to see if anyone had a decent microphone they weren't using. Don't laugh, I got a Linn Sondek for free. I wanted to try and record what each driver sounded like through the different crossovers. No luck though. I don't have an SPL meter, so I can't take any measurements unfortunately.

Are you sure your speakers came with the midrange driver wired out of phase with the woofer and tweeter? Or did it seem that way because of their non-standard color coding? It just might be possible that your speakers were mistakenly wired out of phase when they were built.

Yes, it was definitely wired out of phase with the woofer. Had I not read about other peoples similar findings, I would have thought they were wired wrong from the factory, or a previous owner had messed with them. But the negative wire from the terminal block was wired to the positive terminal on the mid, and the positive wire from the L-pad to the negative terminal on the mid. I'm calling the positive terminal on the mid the one that makes the cone move outwards when tested with a 1.5v battery, not the red terminal as designated by the factory.

I could modify my original switch plates to separate the crossover switch and polarity switch on the midrange...

 

[Swerd]

Wish I could help you there. I tried placing a "wanted" ad on a local FreeCycle board to see if anyone had a decent microphone they weren't using. Don't laugh, I got a Linn Sondek for free. I wanted to try and record what each driver sounded like through the different crossovers. No luck though. I don't have an SPL meter, so I can't take any measurements unfortunately.

In the absence of any way to measure the loudness difference, your observations will suffice. I never thought that the lower sensitivity with the new crossover was a significant problem. Any amp I owned, ranging from 35-200 watts, could easily drive them.

Yes, it was definitely wired out of phase with the woofer. Had I not read about other peoples similar findings, I would have thought they were wired wrong from the factory, or a previous owner had messed with them. But the negative wire from the terminal block was wired to the positive terminal on the mid, and the positive wire from the L-pad to the negative terminal on the mid. I'm calling the positive terminal on the mid the one that makes the cone move outwards when tested with a 1.5v battery, not the red terminal as designated by the factory.

I could modify my original switch plates to separate the crossover switch and polarity switch on the midrange...

Don't make any mods based on what I say alone. I think you understand very well what is going on, and I trust your observations.

I'm trying to remember what exactly I saw when I modified my L100s four years ago. If I recall, when I removed the 12" woofer, I disconnecting the wires at the woofer's spring-loaded terminals leaving the wires attached at the crossover board. But I left the midrange and tweeter in place on the front baffle because I could easily get to those wires once the woofer was removed. The mid was isolated from the rest of the cabinet by a cardboard tube with a closed end. All I did was cut the mid and tweeter wires near the crossover board leaving about 5" of wire still attached to those drivers. When I tested their polarity, I used those wires and noted which color was positive. So I never did see the backs of those drivers or the markings on their terminals. So it is possible that the midrange was wired out of phase, but I never was aware of it. The frequency response curve with the original crossover doesn't seem to reveal anything obviously out of phase, but with all its ups and downs, I'm not sure I could recognize if the midrange was out of phase.

 

[bwilkinson]

When I wired mine, the mid was out of phase as well (per the wiring) with the JBL crossover. I wired it in-phase using the battery test when I used the Murphy crossover.

 

[Swerd]

When I wired mine, the mid was out of phase as well (per the wiring) with the JBL crossover. I wired it in-phase using the battery test when I used the Murphy crossover.

Thanks for the info. It does seem clear that JBL did wire the mid with opposite polarity.

 

[91boz]

Swerd, Where did you get the crossover components for the JBL 100's?

I have an account with Mousser but need more details on the Capacitor voltages and the inductors.