The Vintage JBL West Coast Sound becomes the…

[Kapitan_Nemo]

How long do you expect those 9 volt batteries to last

Batteries should last about 1 or 2 years. You can only use 1 x 9V.

 

[Kapitan_Nemo]

I've seen this mentioned before, but I've never understood the reasons behind the design. Do you have a link that would explain this?

As promised yesterday. Here you have one of the most interesting topics on this topic:

http://www.audioheritage.org/vbulletin/showthread.php?8111-Charge-Coupling-on-the-Cheap

 

[highfigh]

It would take a long time to write about it. I read once on one of the forums about powering the speakers with batteries. JBL has successfully applied this patent in some high models.
The JBL "charge-coupled circuit" replaces a single cap with a pair of series-connected caps of twice the value of the original single cap, the center-point between the cap-pair is attached to a battery in series with a 100K to 1M resistor, and the other side of the battery is attached to circuit ground. This polarizes both caps to the DC voltage of the battery, so the caps never go through zero-crossing. 9V is a better choice than 1.5V batteries, since loudspeaker-level signals fairly frequency pass through the 1.5V threshold, but 9V is getting pretty loud.
Building a new crossover I decided to try this patent. The effect exceeded my expectations.

What happens when you exceed 9V? That comes to about 10 Watts.

 

[Kapitan_Nemo]

What happens when you exceed 9V? That comes to about 10 Watts.

This does not affect the gain. After using a larger voltage, you will not hear more or less power. Rather, it is about strengthening the capacitor's polarization. This patent allows you to use cheaper capacitors. It is not without significance, however, which capacitors we will use. The MKP will behave differently and the oil will behave differently. Any voltage should be assembled based on the controller. There is no ready-made prescription for it. You must test yourself. I only know that this treatment gives us an amazing view and a soundstage similar to life.

 

[highfigh]

This does not affect the gain. After using a larger voltage, you will not hear more or less power. Rather, it is about strengthening the capacitor's polarization. This patent allows you to use cheaper capacitors. It is not without significance, however, which capacitors we will use. The MKP will behave differently and the oil will behave differently. Any voltage should be assembled based on the controller. There is no ready-made prescription for it. You must test yourself. I only know that this treatment gives us an amazing view and a soundstage similar to life.

Gain? What gain, from the speakers or crossovers? They don't provide gain!

Crossover caps are usually non-polar and speaker manufacturers had already used cheaper caps.

You're aware that any 'image' of stereo is an illusion, right? This sound isn't the actual placement of the musicians in a studio when most music was multi-tracked, it was created during mix-down and no, you won't hear it 'exactly the same as it sounded in the studio', for too many reasons to list.

If you short one cap, kiss your amplifier and/or driver(s) goodbye.

 

[Swerd]

I read some of those links, and I still don't understand just how using charged capacitors helps the sound quality.

If I understand what I read, the battery raises the voltage range at which the capacitors operate. Without a battery, voltage fluctuates as a sine wave between plus and minus voltages around zero volts, the dotted line in the figure below:

With the battery, voltage is offset above the zero voltage level, never crossing it.

Zero volts is a mathematical concept humans use to describe the voltage level between plus volts and minus volts. I don't think the electrons care that it's zero. And I don't understand how a DC voltage offset can affect sound quality in a speaker that uses charge coupled capacitors in crossover circuits.

Please, if anyone can explain this, I'd like to hear it.

 

[highfigh]

I read some of those links, and I still don't understand just how using charged capacitors helps the sound quality.

If I understand what I read, the battery raises the voltage range at which the capacitors operate. Without a battery, voltage fluctuates as a sine wave between plus and minus voltages around zero volts, the dotted line in the figure below:
View attachment 28570

With the battery, voltage is offset above the zero voltage level, never crossing it.
View attachment 28571

Zero volts is a mathematical concept humans use to describe the voltage level between plus volts and minus volts. I don't think the electrons care that it's zero. And I don't understand how a DC voltage offset can affect sound quality in a speaker that uses charge coupled capacitors in crossover circuits.

Please, if anyone can explain this, I'd like to hear it.

I did car audio for a long time and one night, hanging out with a couple of guys with electronics background (one, from college, who studied communications electronics and had started by building kits when he was about 7, and the other gad gone to the local tech school for TV/radio repair)- I mentioned that we could make a bundle by gold-plating fuses for audiophiles. We laughed and laughed. About six months later, they were on the market. DOH!

Zero, as a measurement, indicates a lack of something, although some cultures had no concept of this. This looks like what was done with low power car radios- since a non-inverting amplifier can't go below 0V, the signal to the speakers must be raised enough that it never hits that level AND avoid clipping it, a DC voltage is applied, just enough to give it, let's call it 'floor room', since it's below the signal average. It's not a high current supply voltage and it doesn't kill speakers or crossovers, but the first time I watched a speaker move to a fixed position when I turned the radio's power on, I measured the voltage and found this and then, I asked about it.

This looks like an "I hope this works" idea. I still don't know why people build this stuff when comments like " There are some things that just defy measurement and you wonder why it sounds so good for what it is." come with the explanation of the results. (that was copied from he link provided by the OP).

The builder installed these, made the connections, listened to them- not what I would call an 'unbiased' test.

 

[Kapitan_Nemo]

Gentlemen. It is not my intention to convince anyone of this project. I know from experience that many things in audio are irrational and yet what we hear (if we have this ability) often contradicts a rational definition. I do not know if without a battery power my crossover would sound the same. Now he plays very well. I also know a few people who also use CC (in other speakers) and are very happy. I think it's a waste of time to prove whether this makes sense. For me, it makes sense and we'll end it.

 

[Swerd]

@Kapitan_Nemo

Thanks for your posts. My comments were about the charge coupled capacitor design in general, which I do not understand, and not about your efforts. I do appreciate your intent.

I'm glad to see people are still inspired by this 13-year-old improved crossover design for speakers that were made more than 40 years ago.

 

[Kapitan_Nemo]

I listen to very different music. However, the upgrade of the crossover very clearly contributed to the exquisite play of rock music from the 70's, 80's. Talk Talk, Genesis, Pink Floyd play sensational. Recently, I listened to the Ten Years After record album "Recorded Live" - amazing experiences! I have never experienced this album before. There are a lot of such albums. There would be no parties to write about everything For lovers of progressive rock, I also recommend the album of the Swedish group Tasavallan Presidentti - "Tasavallan presidentti", which also plays with these loudspeakers very well.

 

[GrimSurfer]

Thank you Swerd, and other posters. This has been a very enjoyable and informative thread to read!

 

[jules gerfault]

Hi,

I ordered all parts to build the crossover, but unfortunately, I broke one of my le25... can I replace it with a le25-2, le25-4, or le26 ?
And has someone an idea of the sound of le25 clones sold by simplyspeakers ?

Thanks

 

[Alex2507]

With the battery, voltage is offset above the zero voltage level, never crossing it.

Clearly this is closer to what you want to hear because sometimes the voltage goes to ... E-L-E-V-E-N.

EDIT:

Taking a real look at what was going on in the original xo's, I could design a better xo than that. Holy smokes did somebody ever not want to work the day that design was put to paper. And that's all it takes to cross over at 1.5 and 6 KHz? That's probably enough info for me to open a xo company rivaling JBL. Gonna call it Simian Cross.

 

[Swerd]

I ordered all parts to build the crossover, but unfortunately, I broke one of my le25... can I replace it with a le25-2, le25-4, or le26 ?
And has someone an idea of the sound of le25 clones sold by simplyspeakers ?

Can you view, online, a frequency response curve of any of those tweeters? Pay close attention to the tweeter's behavior in the 1-5 kHz range, and don't worry about what happens above 10 kHz. The intended crossover frequency is 5 kHz, so if the replacement tweeter isn't identical to the original below 5 kHz, it shouldn't matter. If the frequency response curve is at all similar to the LE-25, see below, then you should give it a try.

If the new tweeter seems too loud compared to the mid range (too bright sounding) try adding a resistor, 1 or 2 ohms, between the tweeter and the rest of the tweeter XO network.

 

[downtick]

Nice thread. Much has happened since the thread started and the speaker was made.
A friend want to give me a pair of these, one with damaged mid and a base cone.
Looking at the orginal design makes you chuckle. Those rheostats and first order filters. What were they thinking.
The frequency response curves are really interesting. The woofer goes quite high but is pretty jagged at 6 KHz, the mid is very efficient but is very jagged. The tweeter is nice and flat, extends nice and low , but is dropping off early.
My first reaction, why that midrange? Corporate decision? Clearly the woofer and the tweeter has a flat overlap so a two-way crossover at 3KHz or so could work. Tweeter power handling?
I'd probably try to revive the speaker with new cabinets and retire the mids.

 

[Verdinut]

@Kapitan_Nemo

Thanks for your posts. My comments were about the charge coupled capacitor design in general, which I do not understand, and not about your efforts. I do appreciate your intent.

I'm glad to see people are still inspired by this 13-year-old improved crossover design for speakers that were made more than 40 years ago.

That irrational charge coupled capacitor design might have originally been promoted by a battery or a cap manufacturer to sell more of his products and make more profit. Maybe the founder was related to the founder of Audioquest.

 

[Swerd]

That irrational charge coupled capacitor design might have originally been promoted by a battery or a cap manufacturer to sell more of his products and make more profit. Maybe the founder was related to the founder of Audioquest.

As far as I have read, that design originally came from JBL speaker designers who were highly regarded. It was used in one or several higher-priced JBL speakers sometime during the 1980s. I can't remember which models. Later, it was dropped. I assume, but don't know for certain, that high cost was the reason. No other speaker manufacturer has been interested since then.

 

[Swerd]

Nice thread. Much has happened since the thread started and the speaker was made.

Thanks . I'm amazed at how this thread continues to get attention over the years.

Looking at the orginal design makes you chuckle. Those rheostats and first order filters. What were they thinking.
The frequency response curves are really interesting. The woofer goes quite high but is pretty jagged at 6 KHz, the mid is very efficient but is very jagged. The tweeter is nice and flat, extends nice and low , but is dropping off early.
My first reaction, why that midrange? Corporate decision? Clearly the woofer and the tweeter has a flat overlap so a two-way crossover at 3KHz or so could work. Tweeter power handling?
I'd probably try to revive the speaker with new cabinets and retire the mids.

Chuckle is a good way to describe the original L100A crossover.

Before any of that work was done, I had imagined the ancient 1½" cone tweeter was the source of the problem. I thought if I could replace it, the high-frequency noise would go away. Instead, as you noted, the tweeter was good, but the mid-range was a mess. Loud, but uneven.

Then I wondered if simply eliminating the mid-range would improve things. Dennis Murphy quickly talked me out of that idea. A 2-way speaker with a 12" woofer and a 1½" tweeter does look like it might be crossed around 3 kHz, but remember those frequency response curves were measured on-axis. The large woofer had lost most of it's off-axis sound well below 3 kHz, probably beginning roughly at 1 kHz or below. A 2-way speaker with that woofer would beam narrowly with a 3 kHz crossover point,. As soon as the tweeter took over, that beamed mid-range sound would immediately shift to widely dispersed. Dennis had long ago learned that such designs were poor at creating realistic sounding images, although they sounded OK on-axis. That widely dispersed mid-range was key to a really good sounding speaker.

Dennis said he thought that 12" woofer should be crossed no higher than 400-500 Hz, but the mid-range simply couldn't go that low. So he worked on it until he tamed that mid-range driver, and got it to blend well the woofer and tweeter.

 

[harry1867]

Swerd, after all this time I want to thank you for the posting that has breathed new life into my JBL L100s and my listening pleasure. And of course thanks to the designer Dennis Murphy.
As an electronics novice I prepared a couple of things before proceeding that may be of value to others who follow your lead with their old L100s. First I took the schematic and prepared an in/out spreadsheet of the components. I needed this to translate the schematic into a board layout. The spreadsheet has columns for Part Type, labelled and measured performance values, In and Out connections. Then I did a true size Visio to lay out the components and connections on the board. The visio includes the holes for drilling, for both cable ties (great suggestion Swerd) and some bottom side connections that didn't seem clean on top. Curvy lines are topside connections, straight bottom connections. I taped a print out of the visio to the board before drilling. This made assembly much easier. See attachments.
One thing that mildly concerns me is the measurement I got from the L2071 inductor. It was 0.47 instead of 0.55. If you think this is a problem I will consider replacing them.
In sum: I am enjoying the speakers more than any time since I bought them in 1974. Thanks for your diligence in following up in this thread and making this the most fun and rewarding project I have undertaken in many years!

 

[Swerd]

Swerd, after all this time I want to thank you for the posting that has breathed new life into my JBL L100s and my listening pleasure. And of course thanks to the designer Dennis Murphy.

In sum: I am enjoying the speakers more than any time since I bought them in 1974. Thanks for your diligence in following up in this thread and making this the most fun and rewarding project I have undertaken in many years!

You're certainly welcome. I'm always glad to see responses like yours for this crossover re-design. What a difference a crossover can make! And thanks for those attachments. I'm sure someone will find them useful.

One thing that mildly concerns me is the measurement I got from the L2071 inductor. It was 0.47 instead of 0.55. If you think this is a problem I will consider replacing them.

On face value, I don't think an inductor that is 0.08 mH lower will make much of a difference. It's part of the low-pass section for the mid-range driver, which is part of the mid-to-tweeter crossover at 5 kHz, with a 4th order acoustic roll-off. If that 0.47 mH inductor alters things just a little at 5 kHz, I doubt if it would be a noticeable problem.