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sweet212
11-21-2018, 06:57 PM
Hi Everyone.

I have a pair of 250ti's - the later gloss black early 90's versions.

They sound great except for the top end. The best way to describe it is shreaky/steely - particularly on vocals.

What can I do? Perhaps new caps may help or what about charge coupling the xovers?

What do the experts here suggest?

Thanks in advance.

rdgrimes
11-21-2018, 07:29 PM
The foam damper pads in the 044ti are known to degrade and fall apart. Replacing them requires taking the driver apart. There are a few threads around here about the process if you search.

sweet212
11-22-2018, 07:18 AM
The foam damper pads in the 044ti are known to degrade and fall apart. Replacing them requires taking the driver apart. There are a few threads around here about the process if you search.

Thanks for your reply. I will take your advice.

I think these have the 035ti tweeters - could be wrong. Many years ago the Stereo Review article regarding the 250ti's raved about how sweet the top end was. I expected better.

Mr. Widget
11-22-2018, 08:56 AM
Many years ago the Stereo Review article regarding the 250ti's raved about how sweet the top end was. I expected better.Many years ago they probably did. Speakers do age. Yours may need servicing.


Widget

rdgrimes
11-22-2018, 01:51 PM
Thanks for your reply. I will take your advice.

I think these have the 035ti tweeters - could be wrong. Many years ago the Stereo Review article regarding the 250ti's raved about how sweet the top end was. I expected better.

Ah yes, you have the Special Edition models. Those originally came with the 035ti and I think they even came later with something like a 052ti, but I could be wrong about the later. The same holds true in either case, they age. Although the 035ti is much easier to find to buy used than the 044ti. I'm pretty sure there are still some new reproductions of the 035ti being sold.

Look at your crossover boards for any obvious signs of age like bulging caps. If you want to rebuild the tweets, I'd first find a used pair to buy and experiment on. The good news is that the 035ti is 10 times easier to remove than the 044ti models are.

sweet212
11-24-2018, 04:31 AM
Ah yes, you have the Special Edition models. Those originally came with the 035ti and I think they even came later with something like a 052ti, but I could be wrong about the later. The same holds true in either case, they age. Although the 035ti is much easier to find to buy used than the 044ti. I'm pretty sure there are still some new reproductions of the 035ti being sold.

Look at your crossover boards for any obvious signs of age like bulging caps. If you want to rebuild the tweets, I'd first find a used pair to buy and experiment on. The good news is that the 035ti is 10 times easier to remove than the 044ti models are.

Thank you RD. When you say reproductions - you mean copies of the tweeter by 3rd parties? I had a look at the boxes - they are "Classics" and also marked BQRC or BGRC - hard to read.

Would replacing the caps be an improvement? Made a definite improvement with my old 212's.

sweet212
11-25-2018, 06:24 PM
Thank you RD. When you say reproductions - you mean copies of the tweeter by 3rd parties? I had a look at the boxes - they are "Classics" and also marked BQRC or BGRC - hard to read.

Would replacing the caps be an improvement? Made a definite improvement with my old 212's.

Unscrewed the tweeters - they are 035tia's. For some unknown reason the authorized JBL service center will not recondition these speakers - 035ti's yes but not the 035tia's. What can the difference be, apart from contact placement?

I have 2 options. Buy a Chinese drop in clone or repair the old tweeters. I prefer to keep the original components. Especially as their DC resistance checks out at 3.8 ohms, which I assume is OK.

So how hard can it be for a novice like me to replace the foam?

Who here has re foamed a 035tia tweeter?

Please let me know.

SEAWOLF97
11-25-2018, 09:11 PM
Unscrewed the tweeters - they are 035tia's. For some unknown reason the authorized JBL service center will not recondition these speakers - 035ti's yes but not the 035tia's. What can the difference be, apart from contact placement?

I have 2 options. Buy a Chinese drop in clone or repair the old tweeters. I prefer to keep the original components. Especially as their DC resistance checks out at 3.8 ohms, which I assume is OK.

So how hard can it be for a novice like me to replace the foam?

Who here has re foamed a 035tia tweeter?

Please let me know.

this thread ==>>

http://www.audioheritage.org/vbulletin/showthread.php?29325-044Ti-questions-Help-needed&highlight=044ti+help

is about replacing the foam in 044's, but same procedures for 035 (I think)

BMWCCA
11-26-2018, 03:37 AM
Be very careful when removing the 035ti from your 250ti's not to bend the terminals as you pull off the Faston connectors. The very fragile diaphragm wires inside can be broken if the terminal tabs are disturbed by wiggling the wire connectors. Hold the terminal in place gently with small pliers as you remove the connectors. Don't be tempted to straighten "crooked" terminals! You'll see what I mean after you get them apart. Just be careful and the job should not be that difficult.

sweet212
11-27-2018, 06:11 AM
Be very careful when removing the 035ti from your 250ti's not to bend the terminals as you pull off the Faston connectors. The very fragile diaphragm wires inside can be broken if the terminal tabs are disturbed by wiggling the wire connectors. Hold the terminal in place gently with small pliers as you remove the connectors. Don't be tempted to straighten "crooked" terminals! You'll see what I mean after you get them apart. Just be careful and the job should not be that difficult.

Thank you both. This is not an easy job especially for a ham fisted and impatient one as myself.

The best course is perhaps to buy some renovated 035ti's. The terminals are in a different position being 180 degrees apart. So the top of the cabinets will have to be cut out to accommodate the terminal.

BTW: There is a fluid called ferrofluid - supposed to smooth out the sound of tweeters. Will this work on a 035ti?

sweet212
12-11-2018, 12:06 PM
Well these 035TIA's came apart very easily. The grilles prized off with a ball point pen and the 4 screws were a snack.

They look to my untrained eyes to be in great condition. The foam is 22 x only 3 mm thick, I believe they should just touch the titanium dome. Can that be right? Wouldn't touching the dome mute the sound?

The replacement foam pieces should arrive tomorrow.

Thanking you in advance for any advice.



829818298082979

Earl K
12-11-2018, 12:14 PM
Yes, the function of the foam is ( by lightly touching the inside of the dome ) to mute spurious resonances made by the titanium dome .

:)

SEAWOLF97
12-11-2018, 03:57 PM
Well these 035TIA's came apart very easily. The grilles prized off with a ball point pen and the 4 screws were a snack.

They look to my untrained eyes to be in great condition. The foam is 22 x only 3 mm thick, I believe they should just touch the titanium dome. Can that be right? Wouldn't touching the dome mute the sound?

The replacement foam pieces should arrive tomorrow.

Thanking you in advance for any advice.



be best to take compressed air and blow anything out of the mag gap as long as it's opened.

Don C
12-11-2018, 05:48 PM
I think that your foam is much thinner than it was when new. It's supposed to press up against the back of the dome and conform to it's shape. it should feel springy, not gooey.

sweet212
12-12-2018, 06:05 AM
I think that your foam is much thinner than it was when new. It's supposed to press up against the back of the dome and conform to it's shape. it should feel springy, not gooey.

Thanks for your replies. The maker of the replacement foam says the foam should made hemispherical to match the shape of the dome and about 10mm thick. OK that will definitely touch. Too much contact and too hard will just about cancel all sound and too little will have no damping effect on resonances - a bit arbitrary. The trick is to get light contact - I assume.

However I will try and let you know. I have to solder on new leads as the original leads are too short and just reach the tweeter and make it very hard to install.

Malefoda
12-14-2018, 07:00 AM
Look at JBL's kit.https://www.midwestspeakerrepair.com/wp-content/uploads/2014/08/product_f_i_file_16_15_1.jpg
I've cut mine around the same specs (found other pics at that time) and it pushed quite hard on the dome. Scary but sound was just great. And is still! Just to barely touch is not enough, you want a tad amount of pressure.
http://www.audioheritage.org/vbulletin/showthread.php?35182-4313B-s-066-in-need-of-a-miracle&p=358810&viewfull=1#post358810
Good luck!

sweet212
12-14-2018, 07:07 PM
Look at JBL's kit.https://www.midwestspeakerrepair.com/wp-content/uploads/2014/08/product_f_i_file_16_15_1.jpg
I've cut mine around the same specs (found other pics at that time) and it pushed quite hard on the dome. Scary but sound was just great. And is still! Just to barely touch is not enough, you want a tad amount of pressure.
http://www.audioheritage.org/vbulletin/showthread.php?35182-4313B-s-066-in-need-of-a-miracle&p=358810&viewfull=1#post358810
Good luck!


Thank you Malefoda.

Your story gives me more confidence.

Looking at the domes today I was surprised that there is no spider kind of suspension for the domes. As compared with lower frequency drivers.

Still waiting for the foam replacements in the mail - I think they've got lost.

sguttag
12-15-2018, 02:53 PM
Sorry to temporarily hijack this thread, but a quick question. Did the L250 HF driver (044-1) have the foam or was it just on the titanium stuff as used on the 250Ti?

sweet212
12-16-2018, 07:54 AM
Thank you Malefoda.

Your story gives me more confidence.

Looking at the domes today I was surprised that there is no spider kind of suspension for the domes. As compared with lower frequency drivers.

Still waiting for the foam replacements in the mail - I think they've got lost.

Having bought these speakers a year ago and noticed someone has worked on them. I checked the polarity of the tweeter with the wiring diagram. Sure enough, whoever worked on them connected the black strip wire to the + terminal of the tweeter. According to the 250ti BQ schematic the black stripe connects to the - terminal. I assume I can check the other drivers polarity with a battery at the speakers main input terminal.

rdgrimes
12-16-2018, 09:24 AM
Having bought these speakers a year ago and noticed someone has worked on them. I checked the polarity of the tweeter with the wiring diagram. Sure enough, whoever worked on them connected the black strip wire to the + terminal of the tweeter. According to the 250ti BQ schematic the black stripe connects to the - terminal. I assume I can check the other drivers polarity with a battery at the speakers main input terminal.

On the JBLs, the black stripe always goes to the "-" (black) terminal on the driver.

grumpy
12-16-2018, 05:32 PM
Sguttag... 044 series had foam also.

sguttag
12-17-2018, 06:53 AM
Sguttag... 044 series had foam also.

Thanks for the information...though it sucks. I haven't fired them up in a long time (been a couple of years) but they will go on line in 2019. Since I've reconed the woofers once already and they look like they aren't too far away from needing a refoam job, I'd have to think that the tweeters then would be due for a new set of foams.

Any additional complications on this model versus the others?

sweet212
12-17-2018, 07:25 AM
On the JBLs, the black stripe always goes to the "-" (black) terminal on the driver.


Thank you RD.

sweet212
12-17-2018, 07:30 AM
Thanks for the information...though it sucks. I haven't fired them up in a long time (been a couple of years) but they will go on line in 2019. Since I've reconed the woofers once already and they look like they aren't too far away from needing a refoam job, I'd have to think that the tweeters then would be due for a new set of foams.

Any additional complications on this model versus the others?

I'm still waiting for the foam to come in the post but it should be easy enough to put back together. Would be worth your while to refoam your 044's. I'll let you know how different or not my 250ti's sound.

grumpy
12-17-2018, 08:09 AM
Would be worth your while to refoam your 044's.

Agreed. Last set I had open, the foam had turned to a little pile of goo.

Even if not so completely degraded, the old foam will likely have lost resilience after 30+ years
with little support or damping provided. Patience in disassembly is your friend.

sweet212
12-21-2018, 05:51 PM
On the JBLs, the black stripe always goes to the "-" (black) terminal on the driver.

Someone has messed around with the terminals. The black stripe lead with female spade terminal connects to the positive (+) speaker connection. This means the tweeter is in anti-phase - unless the connection to the xovers is not also swapped around.

8305283051

rdgrimes
12-21-2018, 07:46 PM
Someone has messed around with the terminals. The black stripe lead with female spade terminal connects to the positive (+) speaker connection. This means the tweeter is in anti-phase - unless the connection to the xovers is not also swapped around.


If you're trying to suss out the crossover wiring, the tech sheet links found here (http://www.audioheritage.org/vbulletin/showthread.php?10661-JBL-Consumer-Tech-Sheet-Links) should help. Shows polarity, pin numbers and color codes.

sweet212
05-23-2019, 06:23 AM
I resurrected this thread to let you know the results.

I have been very busy but my 250ti's are finally back together.

Re-foaming the 035's was easy. The tweeters are now less prominent - they sound better. Excellent result.

However someone who owned these speakers before rewired them and the color coding does not match. Its almost impossible to trace the polarity through the crossovers because speaker resistance for either polarities is almost identical.

The only way to ensure that the speakers are correctly connected IMHO is with a sound level analyzer.

Your comments and ideas are most welcome.

Robh3606
05-23-2019, 07:59 AM
You should verify with measurement. But be careful with the polarity as in the tech sheets. If you look closely at the TBQ it is actual driver acoustic polarity. Looking at the sheet it looks like your tweeter might be correct. You would want a negative on the positive to get a negative acoustic driver output. It would be nice if we knew if the 035 is plus on plus.

Rob:)

opimax
05-23-2019, 10:06 AM
I worked with some 250s have 4 all TI now , new xovers in one set that are Charge Coupled that was not the original Xover for that model. I remember finding the diagrams very confusing and possibly incorrect. Make sure you have the correct diagram too. There 3 or 4 version of 250 speakers, 3 TIs i think including European version and 1 set that was Charge Coupled from the factory. Part of the confusion comes from JBL switching to the current standard or polarity during the time the 250 series was built. Original woofers went inward when touched to a battery to test, positive terminal to the positive battery . It switched at some year but i would think your version is past the switch. I was never (and still am ) sure if I have polarity each driver 100% correct.

you have gold tweeter , never let it go!! rare

sweet212
05-24-2019, 07:40 AM
I worked with some 250s have 4 all TI now , new xovers in one set that are Charge Coupled that was not the original Xover for that model. I remember finding the diagrams very confusing and possibly incorrect. Make sure you have the correct diagram too. There 3 or 4 version of 250 speakers, 3 TIs i think including European version and 1 set that was Charge Coupled from the factory. Part of the confusion comes from JBL switching to the current standard or polarity during the time the 250 series was built. Original woofers went inward when touched to a battery to test, positive terminal to the positive battery . It switched at some year but i would think your version is past the switch. I was never (and still am ) sure if I have polarity each driver 100% correct.

you have gold tweeter , never let it go!! rare


Yes thanks Opimax and Robh.

I changed the connections to the drivers according to the resistance through the crossovers but that was not conclusive as the resistance was almost exactly the same. Only changed one speaker and left the other as it was. Actually they sound almost identical - with the modified crossover sounding less boomy.

I think the only way to be sure is to test the speakers with a sound level meter. Can anyone recommend a decent setup to do this?

Robh3606
05-24-2019, 08:22 AM
I think the only way to be sure is to test the speakers with a sound level meter. Can anyone recommend a decent setup to do this?

You should really use a proper measurement system if you can to look for suck outs to verify if the drivers are connected improperly. You might be able to tell if you used a tone/band limited noise at the crossover frequency and checked the spl level and then reversing the phase to see which way is louder. The louder one is the correct one.

Rob:)

Malefoda
05-25-2019, 09:56 AM
I think the only way to be sure is to test the speakers with a sound level meter. Can anyone recommend a decent setup to do this?

MiniDSP claibrated (compensation file) https://www.minidsp.com/products/acoustic-measurement/umik-1 then the software of your choice =)

sweet212
05-26-2019, 12:46 PM
MiniDSP claibrated (compensation file) https://www.minidsp.com/products/acoustic-measurement/umik-1 then the software of your choice =)


$75 - very reasonable thanks Malefoda and Robh.

What about software? What is the most economical and use-able software?

Odd
05-26-2019, 01:07 PM
REW
Room Acoustics Software (https://www.roomeqwizard.com/)

Free and very good.
A lot of info online.