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Green Wagon

JBL 250Ti - Charge of the capacitor brigade :D

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As some of you know, I just can't even begin to stomach electronic repairs anymore.

Speakers is where I want to spend my time now.

As such my first job under the new regime is an absolute doosey........

The only other person I know of that has done this job has vowed to never do another one.

I don't think it's that bad. Just time time consuming.

Between other things that needed my attention, these took me almost a full month.


 

Without further ado, I present you with the JBL 250Ti Charge Coupled Crossover build....
 


 

Were going from this. (As far as I'm aware no one has ever measured the inductor dcr's - This schematic is my edited version and also includes a resistor 'missed' from the original)

 

N250Ti Schematic.jpg
 


 

Too this..


 

n250ti biased.jpg

 

These are the actual speakers, The four way ones on the right. Minus the 14" bass drivers that were off for a rebuild. The ones on the left are his L212 JBL's.

 

1.jpg


 

Bass driver removed you can see the factory crossover.

 

2.jpg


 

The back of the speaker has the binding posts and the attenuator jumpers for the Mid, High frequency, and the Ultra high frequency drivers (As labeled by JBL)

 

3.jpg


 

BIG crossovers. Remember, thats a 14" hole. And as you can see from the gent behind the speaker, they are taaaaall.

 

4.jpg


 

Old crossover removed with the old 3 way crossover for the L212 for reference (The L212 is the other 'wide baffle' speaker in the above pic).

 

5.jpg


 

Just a few parts required.

 

6.jpg

7.jpg


 

Original crossover is a two layer beast. This is the upper board lifted to show the connections to the attenuator posts.

 

8.jpg


 

Close up of the posts.

 

9.jpg


 

After removing the top board and most of the inductors.

 

10.jpg


 

Back board finally stripped to the point I wanted.


 

11.jpg


 

Several screws had to be cut from the inside. To prevent rattles I used a little super glue then epoxy to lock them solid.


 

12.jpg


 

To make the new binding posts fit I had to 'press' some washers onto the shaft first.


 

13.jpg


 

Then glued them to the back board with epoxy which fills in the gap and make it a solid assembly..

 

14.jpg


 

Before reinforcing the whole lot with more epoxy and 9mm plywood before bolting it all together.


 

15.jpg

16.jpg


 

Inductors glued to back board with liquid nails.


 

17.jpg


 

New top board is 9mm ply. Original fiberglass pcb obviously had issues with rattles as they had been 'packed out' with bits of foam blocks.

 

18.jpg


 

Um, would you like a resistor with those capacitors ?

 

19.jpg


And after the bypass caps had been installed.


 

20.jpg


 

The charge coupling resistors.

 

21.jpg


So here comes the time consuming part. Part one that is. Wiring the inductors to the top board.


 

22.jpg


 

Followed by the second part of the time consuming part. Wiring the attenuator studs to the everything else.


 

23.jpg


Almost done. I used a bit of wadding folded in half to make sure none of the wire could rattle.


 

24.jpg
 


 

Fold the two halves together, and screw it in place from the other side of the back board.

Old crossover, New crossover.

 

25.jpg


 

Old crossovers weigh in at 3.466Kg.


26.jpg


While the rebuild is 5.07kg.


 

27.jpg


 

And finally, after I dressed the connection leads for the drivers.


 

28.jpg


The back. Cleaned and ready to be reinstalled into the cabinets. Complete with a 9v battery holder and terminal clip.


 

29.jpg


 

Now don't go asking me how they sound.

I never heard them with the original crossovers, and I haven't heard them (yet) with the new crossovers.

So any A/B comparison from me is just useless at best.

But, I'm sure the owner will be along to make his thoughts known.

He only just picked these up this arvo, so needs to let the rebuild bass drivers and the crossover break in.


 

In case you were wondering, and even if you weren't, these monsters I believe tip the scales at around 75kg. Each.

 

Edited by Green Wagon

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Gulp! Awesome work there mate. keen to hear the owners thoughts. These JBLs get a lot of good press.

 

Cheers

 

M

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You would have to be a passive [crossover] aggressive to tackle that!

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Thanks guys.

Thomo make funny :D LOL.

Yes it was a daunting task.

But I practiced what I preach to others when doing large jobs.


 

How do you eat an elephant ?

One bite at a time. :D


 

Oh yes. I couldn't see any way of removing the two upper tweeters so was concerned about how to get at their wires.

Then the owner showed me JBL's neat trick.


 

A sub panel held in place with a few screws.

Brilliant. Allows easy access to the very top tweeter, and the one under it (in it's own sub enclosure).


 

30.jpg


 

Owner has said to me that they sound nothing like any JBL he has ever owned before in his life. And thats quite a few.

I'm dying to hear them myself. But I know the parts and rebuilt bass drivers will take time to settle down.

So I'm trying to leave him alone so he can enjoy them in peace.

And break them in for me ;)

 

Edited by Green Wagon
Trying to compensate for site formatting issues.

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Holy cow, having recently rebuilt my own JBL crossovers I can feel your pain however mine was a mere flesh wound compared to that job!

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A very interesting speaker.  Here's a contemporary (1985) review that pitches the opinions of J Gordon Holt against Anthony H Cordesman:

 

http://www.stereophile.com/content/jbl-250ti-loudspeaker#P5KK8urcEcDfwXXI.97

 

The concept of "live-sounding but harsh" vs "polite but boring" speakers really resonates with me.  I suspect electronics and source technology have improved to the extent that the choice is less stark now and you can get more of a nice "live-sounding but not harsh" compromise, which is the ideal I'm striving for.

 

But I still recognize that dichotomy of listener preferences and I think it's part of the reason there's such diversity in speaker design.  We all seem to need a different blend of qualities/compromises for music to sound "real".  Sometimes, the difference in preferences can be quite stark and it's the fundamental reason speakers are such a personal choice.

 

I guess it makes this hobby more interesting that we don't all enjoy exactly the same flavours and textures.

Edited by Tony M

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So I have been running the caps and the new woofers in for a bout 15 hours or so this weekend.

 

I think the caps have started settle in but I suspect woofers will need a little longer for the spiders and foams to loosen up properly.

 

As per my initial listening sessions with these they are huge departure from the traditional JBL sound. They are so well balanced from top to bottom, not one frequency outshines the other. Everything is equally as balanced. But not lets get carried away, they are dynamic as hell and the bass is prodigious.

 

They image superbly and the soundstage, as you would expect is incredibly tall. The most impressive aspect of them is the detail in the soundstage, instruments are clearly defined and layered. The older JBL's can get a tad cluttered with demanding material.

 

Since the charge coupling I am very impressed with the mid-range, the bottom range of male vocals is now completely full. There is no real tonal difference which i expected but there is certainly less grain. The tweeters are very crisp and superior to the older JBL titanium tweeters. I would say I prefer them to 2405 which is a fantastic tweeter.

 

From left to right I feel like I am being presented with a humongous image of the performance. Its like going to watch a movie at the Imax theatre when you are use to your 50" tv at home.

 

I could carry on about how great they are but my literary skills and ability to express what I hear are not the greatest.

 

They are excellent speakers and have been taken to an entirely new level. As with my L212's they will be with me forever.

 

Regarding that stereophile review. I would take that with a grain of salt. Gordon Holt would be in the minority of people who are not impressed by these speakers.

 

As usual Nigel did a fantastic job, I installed them and they worked first go. A statement to Nigels workmanship. He is a beast.

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So glad your happy Chris.

With all the wiring I was worried I'd get something wrong. Even after checking them 3 times.

Guess it's like a new born. Your always worried something isn't quite right :)
 

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As most of you know, I am a bit of a crossover tinkerer and I would like to say that's a fine looking job 

 

 

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7 hours ago, Zaphod Beeblebrox said:

Best.JBL.speaker.ever.

 

With a passive Xover like that...:unsure:

 

Surely active is the way to go...Blimey!!

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3 minutes ago, Tasebass said:

 

With a passive Xover like that...:unsure:

 

Surely active is the way to go...Blimey!!

 

I was thinking this also. But a 4-way? No thanks......

 

I would only consider doing it if I had a Deqx and then you need 2 for a 4-way. Your looking at over 6k just for the Deqx. Than factor in the extra amplifiers. It would cost well over 10k.

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