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

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

  • Yes, absolutely (but carefully)

    Votes: 3 100.0%

  • No

    Votes: 0 0.0%

  • I honestly have no idea, but I want to vote

    Votes: 0 0.0%
  • Total voters
    3
  • Poll closed .
I have a pair of Q10 with this issue. One tweeter had a VC that was rubbed open. The other one VC detached from diaphragm due to sticky ferrofluid.I did try rubber cement on the detached one, and the fix seemed to work fine. Call to KEF said they don't have any replacements left.

I saw these and decided to give it a shot http://www.ebay.com/itm/New-10-pcs-ID-19-43mm-4-ohm-19-43-mm-tweeter-silk-diaphragm-speaker-voice-coil/282494040806?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Perfect fit, and I decided to just replace diaphragm/VC on both tweeters. They measured 4.8ohm on my cheapo multimeter, which is the same as what my one good VC measured.

Sounds great right now, I'll probably try to measure them in REW later tonight. Unfortunately, I don't have before measurements since I bought these damaged.

*Update, measured with the following results
VTOVP8q.jpg


You can see some of the other speakers I've measured here https://imgur.com/a/J5yNn

Notice how 3 of the speakers have 3 dips in the same region. I think that's a room node that happens with dome tweeters. The BG speakers don't show the same dips, since that one's got a planar tweeter.
 
Last edited:
Those are beautiful KEF speakers! I also have a pair of C55s that I want to recap (I started another thread on this). Just out of curiosity, do the tweeters have ferrofluid? I'm scared to do this after reading about your experience. :oops:
 
TerryB123 said:
It's unclear from the eBay ad, Are These single voice coils or are they selling lots of ten each?
Click to expand...

Yes, lot of 10, the seller also sells them in pairs. But I figured I'd get some extras just in case I messed up, and shipping takes around 3 weeks. It was a last resort for me as KEF no longer carried replacements, and used examples on ebay were expensive, and beat up visually. The fit was perfect, lined up the edges with the housing, and VC dropped right into the gap, even the leads lined up right with the stock solder points.
 
bigx5murf said:
Yes, lot of 10, the seller also sells them in pairs. But I figured I'd get some extras just in case I messed up, and shipping takes around 3 weeks. It was a last resort for me as KEF no longer carried replacements, and used examples on ebay were expensive, and beat up visually. The fit was perfect, lined up the edges with the housing, and VC dropped right into the gap, even the leads lined up right with the stock solder points.
Click to expand...
Thanks, that's what it looked like. I ordered a stash this morning.
 
TerryB123 said:
Thanks, that's what it looked like. I ordered a stash this morning.
Click to expand...

Just to be sure, you need them for NT19 tweeters right? I think for NT25 you'll need 25mm, and I'm not sure if you need 4ohm or 8ohm, I'm also not sure how those will fit.
 
Great blog on this matters, it is not ease to find answers to this questions.

From "B160 woofer and NT25 Tweeter assembly - to remove the tweeter, one must first desolder the leads running to the HF terminals, then carefully remove the three perimeter screws holding the magnet to the basket. Then removing the tweeter is as easy as removing the center screw and carefully pulling it off the magnet."

It seems to me that you are unmounting the magnet from the woofer, to access the tweeter. Maybe I misundertood, but I thik it is dangerous. In my case, Kef Q60, it is possible to take the tweeter from the front, only remove the central screw and push to overcome the magnets attractions (not much)

SANY5240.JPG

SANY0684.JPG
This is the old ferrofluid
SANY0687.JPG
The clean magnet
SANY0688.JPG
The magnet refilled with new ferrofluid
SANY0690.JPG
Some measurements, before and after. Green is before repair. Blue is without ferrofluid. Yellow is with new ferrofluid. The relative levels of the measurements are correct, not the absolute.
Reparacion respuestas.png
 
Has anybody tried this donor voice coil?
The former material, looks aluminum, like the original. I can't see the number of turns in the pictures. NT25 has arround 9.
I only have one with the voice coil damaged, but I can't reconect it. When I disassembled it, i broke the wire to the coil, because the ferrofluid separated the coil from the diaphragm. I do not forgive myself

SANY0691.JPG

Does anybody know how to tear a small piece of coil wire to solder it again?.

It would be a pitty, spend time and money to replace, and finally get an obvious difference between both channels.
 
Last edited:
Raul Perez said:
It would be a pitty, spend time and money to replace, and finally get an obvious difference between both channels.
Click to expand...

That's why when I successfully repaired my NT19, I decided to just do the swap on my good one as well. Although in my case, my good one was damaged as well and I had to add mass and glue the diaphragm back onto the voice coil. I did briefly compare the two a little bit. I actually thought the replacement sounded more detailed than the original. In hindsight, I probably should've measured them both first. Anyway, diaphragm/vc swap is obviously a last resort repair when you have no other options.
 
Raul Perez said:
Great blog on this matters, it is not ease to find answers to this questions.

From "B160 woofer and NT25 Tweeter assembly - to remove the tweeter, one must first desolder the leads running to the HF terminals, then carefully remove the three perimeter screws holding the magnet to the basket. Then removing the tweeter is as easy as removing the center screw and carefully pulling it off the magnet."

It seems to me that you are unmounting the magnet from the woofer, to access the tweeter. Maybe I misundertood, but I thik it is dangerous. In my case, Kef Q60, it is possible to take the tweeter from the front, only remove the central screw and push to overcome the magnets attractions (not much)

View attachment 1031173

View attachment 1031174
This is the old ferrofluid
View attachment 1031176
The clean magnet
View attachment 1031177
The magnet refilled with new ferrofluid
View attachment 1031178
Some measurements, before and after. Green is before repair. Blue is without ferrofluid. Yellow is with new ferrofluid. The relative levels of the measurements are correct, not the absolute.
View attachment 1031181
Click to expand...
Hi, I've just replaced the ferro fluid in my NT25's from my 103/4's.
I also didn't remove the magnet, just the tweeter retaining screw. I must admit I had to play around with one due to a strange destorsion sound. Seemed like the tweeter was rubbing on the mid range unit/too close to the gap.?
Just repositioned it and everything is fine now. Not much room for error on these.
Anyway the diffence is quite astonishing.
Going to do my Ref Model ones next.
 
bigx5murf, do you have any of those ebay domes left? I'd like to buy some but dont want to wait 3 weeks! BOTH of my diaphragms ripped in the same way, prob because the ferrofluid locked up the coils.
20171128_105030.jpg 20171128_105043.jpg
 
Just want to say thanks to all the info in this thread. One of my Q90 tweeters was completely inoperable and it looks like this was probably due to the voice coil no longer attached to the diaphragm. Either way, i cleaned up and added new fluid, reattached the VC and it sounds fantastic. Now my left speaker seems dull, time to repair the other tweeter too. I used elmers glue. It worked perfectly.
42cadd.jpeg
 
Just scored a pair of these reference speakers locally. Havent inspected them yet - they look OK cosmetically however havent heard.

I was lucky enuf to score a pair of Q80's that the seller thought a tweeter had blown on for $50 - turns out it was just a loose linking plate on the bi-wiring plate at the back. Those tweeters work fine so I have a backup pair of tweeters, I will pull those speakers apart and try to sell of the mid/bass driver and xover.

So the only mystery to sort out is the condition of the foam on the internal bass drivers in my new 103.4's. I also have a pair of 104.2's, so I really dont need more KEFs! But I do love the coincident driver arrangement......
 
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