KEF NT25 Tweeter Refurbishing (with Pictures) - and a question

Use adhesive to re-join the Voice Coil and Diaphragm?

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Hmm, don't think so, I made pictures before starting disassembly and put all wires back into the same position

Any idea if there was an issue in the crossover before attempting repair?

Anyway, sounds like the crossover just needs a recap. There are full cap kits for the 103.2, not sure how different that is from what you have. May want to contact falcon acoustics directly. Recapping a crossover should be easy if you can replace caps on a PCB. Have you taken a look at the crossover for any obvious issues such as evidence of heat issues?
 
Furriofluid removed, tonight regluing the one VC that came loose from the diaphragm when dismantling.

This step is my biggest point of stress.
 
All seems to have went well.

Removed old pasty furriofluid, reattached the one loose VC, replaced furriofluid and re-assembled.

Now let's see if they still have continuity and make noise:)
 

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Bought 103/4s in 1994. Always loved the sound. A few years ago started sounding really muddy. Read the forums. Figured it was ferro fluid. Took them apart. Refoamed all 4 woofers. Cleaned and replaced ferro fluid. One tweeter diaphragm was disconnected from voice coil AND a red tiny wire that connects to voice coil was disconnected. Tried to resolder it. Put them back together. Hooked up to amp with mixed results.still mostly muddy.

1. Potential issue - positive (red) tiny wire was still not connected to the tweeter.
2. Potential issue - when I reattach d the diaphragm to the voice coil glue might have bled to the dome of the diaphragm itself.
3. Potential issue - capacitors could be bad. Eyeballing them they seem okay. But they are 24 years old.
4. Potential issue - too much new ferro fluid in cavity in magnet.

Thoughts on prioritizing these? I'm thinking new caps all around as a first attempt.
 
Bought 103/4s in 1994. Always loved the sound. A few years ago started sounding really muddy. Read the forums. Figured it was ferro fluid. Took them apart. Refoamed all 4 woofers. Cleaned and replaced ferro fluid. One tweeter diaphragm was disconnected from voice coil AND a red tiny wire that connects to voice coil was disconnected. Tried to resolder it. Put them back together. Hooked up to amp with mixed results.still mostly muddy.

1. Potential issue - positive (red) tiny wire was still not connected to the tweeter.
2. Potential issue - when I reattach d the diaphragm to the voice coil glue might have bled to the dome of the diaphragm itself.
3. Potential issue - capacitors could be bad. Eyeballing them they seem okay. But they are 24 years old.
4. Potential issue - too much new ferro fluid in cavity in magnet.

Thoughts on prioritizing these? I'm thinking new caps all around as a first attempt.

1- Can you read continuity and impedance from the connection wires after reconnecting the red wire?
2- Glue bleeding to the diaphragm shouldn't make much of a difference unless it added significant mass, afterall a doped fabric soft dome is just this
3-Capacitors could be bad, but no way to know for sure unless you have a capacitance measuring device (these aren't cheap), the replacement caps you can buy from falcon acoustics will be 5% tolerance, and not 2% like the originals.
4-too much fluid would probably lower output, do you have a way to run and measure a signal sweep? You'll need a calibrated measurement mic, a USB audio interface with mic preamp, a laptop and a copy of REW
 
1- Can you read continuity and impedance from the connection wires after reconnecting the red wire?
2- Glue bleeding to the diaphragm shouldn't make much of a difference unless it added significant mass, afterall a doped fabric soft dome is just this
3-Capacitors could be bad, but no way to know for sure unless you have a capacitance measuring device (these aren't cheap), the replacement caps you can buy from falcon acoustics will be 5% tolerance, and not 2% like the originals.
4-too much fluid would probably lower output, do you have a way to run and measure a signal sweep? You'll need a calibrated measurement mic, a USB audio interface with mic preamp, a laptop and a copy of REW


Thanks for input. I'm doing a frequency response test tomorrow and will post results.
 
positive (red) tiny wire was still not connected to the tweeter.
If this is right - this could be the end of the coil. If its loose, it will need to be resoldered to wherever it came off - either a tag or another wire. The red is copper insulation which will need to be very carefully scraped off to allow soldering of the wire underneath
 
U can also find the N25 tweeter in other speakers. I sourced a replacement in a 100c center channel. They usually run cheaper then the tweeter by itself...
 
I found a pair of Q15 locally for a good price, and met the seller today. He demo'd them for me, and I thought great, everything works, I won't need to do anything.

Got them home, put them into my desk setup, and right away I noticed one had lowered output in the highs. Listened more closely, and found that one's also buzzing in the tweeter a little. Looks like I'll have to open up these tweeters regardless.
Anyone else notice the Q15 are boomier than the Q10?
 
I had the Q15.2 for a few years and these were far from boomy, I must say. Even a bit too dry for my taste, and that was the reason I parted with them in the end. Partnering them with a REL sub didn't solve this. I'm talking about the Mk2 version of course, but I don't think these differ much from the original Q15. Perhaps the decreased treble makes the sound balance more boomy, making bass and mid too strong by comparison?
 
Pair of 103/4 from 1994. Muddy tweeters. followed these forums to clean and replace ferrofluid. Worked on one speaker. One of the small voice coil wires came off when I was pulling the tweeter apart. I tried to reattach and think I failed. See attached freq response test. Using freeware so its not a smooth sine wave. Questions:
1. What are the crossover frequency settings on the speaker? I have not been able to find it anywhere.
2. Could the drop off in frequency be from a capacitor?

Free software I usedLeftFreqResp.png
Audio pick up on Spectroid app for Android with attached mic
AudMes frequency generator
 
Literally refurbing the NT19 my KEF Model 90C center channel right now!

After getting the hang of this, I should be done in about 20 mins. Should have enough time tonight to refurbish the NT19s in my C55s downstairs too!

I'll post a detailed write-up for both

How did you manage to separate the magnet? I have my nt19 tweeter in front of me and I'm applying plenty of force but they won't budge a milimeter.
 
How did you manage to separate the magnet? I have my nt19 tweeter in front of me and I'm applying plenty of force but they won't budge a milimeter.

I found the diaphragm / voice coil assembly came off the magnet with copious isopropyl alcohol and careful razor blade surgery. Be VERY careful, it is VERY easy to slip and harm the voice coil. Additionally, because the voice coil is now cast in cemented ferrofluid, it has a high chance of bending / breaking if removed without due care. Maybe others used different methods; good luck.
 
I found the diaphragm / voice coil assembly came off the magnet with copious isopropyl alcohol and careful razor blade surgery. Be VERY careful, it is VERY easy to slip and harm the voice coil. Additionally, because the voice coil is now cast in cemented ferrofluid, it has a high chance of bending / breaking if removed without due care. Maybe others used different methods; good luck.

Is it glued on?
 
I'm changing the ferrofluid in my SP1240's and was wondering if you used super glue to reattach the phenolic to metal when re-assembling. I'm going back and forth on different adhesives, the super glue may set up too fast. You also want to be able to service the tweeter again. Looks like a very thin clear glue was used originally. What did you use?
 
I'm changing the ferrofluid in my SP1240's and was wondering if you used super glue to reattach the phenolic to metal when re-assembling. I'm going back and forth on different adhesives, the super glue may set up too fast. You also want to be able to service the tweeter again. Looks like a very thin clear glue was used originally. What did you use?

I used Aileen's tacky glue but very thin applied with my finger tip. I did not however glue the screen on. I felt that the magnetic force was good enough.

IMG_20190315_211717.jpg
 
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