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KEF 105/3 Tweeter Ferrofluid Replacement - NT25 SP1240

Randy Master

Randy Master

New Member
Acquired a pair of KEF 105/3 a couple of months ago. The mid and bass sound fantastic, but not the highs. It feels kind of dull and not as lively as the 107's tweeter (T-33) - I AB'd the two speakers. After reading a lot of postings from the internet, I suspect the FF may be the culprit. I was told that 105/3's tweeters are very fragile and very hard to replace the FF without damaging them.
I started this thread for people have the subject experiences to share the information regarding the FF replacement for the KEF T25 tweeters especially SP1240. Hopefully this can help others who also want to replace the FF for their beloved KEF Uni-Q tweeters in the future. In the meantime, I will also try to replace the FF for my 105/3. I will post my experience here no matter successful or not... :)
 
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First off Welcome to AK . There are a few threads on how to replace the FF on Kef speaker . I did a couple pairs , 104.2 and 103.4 speakers not difficult. I would check out the speaker forum here and on utube . Good luck
 
@greymatter Thanks for the advice. I found a few threads talking about the FF replacement on NT25s, but they are not SP1240. Based on the observation, the SP1240 has the wires glued to the side of the unit, to replace the FF you need to ply loose the very thin wires in order to detach the voice coil from the magnet, I think that may be the hard part and need to be very careful not to damage the unit. Attaching a picture of it here to illustrate...
 

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Did you checkout Utube ? have not done this specific model . Maybe someone with experience with your model will chime in .
 
I completed both tweeters (NT25 SP1240) and now they sound fantastic (in fact, I replaced the donuts for all four woofers as well). I am going to upload some pictures of the tweeter FF replacement photos just in case someone out there also want to do the same. Hope this will help. I also have a few videos, if anyone need to watch them, please let me know and I will upload them as well.
 

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It only allows me to upload 10 pictures per message posting. So I will upload the second batch here.
 

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Thanks Randy. I have the 105/4's and I think they have the same tweeter. This will shure help when I change the ferro fluid.:banana:
 
Thanks for sharing. It takes some guess work to figure out what every photo is about. Can you explain how you removed the tweeters and separate the voice coil from the magnet??
 
@kwingylee You are very welcome. Sorry for not adding explanations for each photo. I will add them when I have time (may be create a step by step instruction). :)
Separating the tweeter's voice coil and magnet is the trickiest part of the FF replacement. The way I did it is to use a pocket knife aiming at the correct separation point (I put a red arrow in the pic 006) then use a miniature hammer (or something similar) to tap on the knife. I would strongly suggest to firmly hold the knife with 2 fingers at the right depth to prevent the knife cutting too deep into the tweeter and damage the voice coil. Do this on all sides of the tweeter (and also be patient, you don't need to separate it in one shot). Keep on doing it until one spot started separating then move on to the next spot. It may take a few minutes to complete the separation task but it is definitely doable. Good luck. :beerchug:
 
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Randy Master said:
@kwingylee You are very welcome. Sorry for not adding explanations for each photo. I will add them when I have time (may be create a step by step instruction). :)
Separating the tweeter's voice coil and magnet is the trickiest part of the FF replacement. The way I did it is to use a pocket knife aiming at the correct separation point (I put a red arrow in the pic 006) then use a miniature hammer (or something similar) to tap on the knife. I would strongly suggest to firmly hold the knife with 2 fingers at the right depth to prevent the knife cutting too deep into the tweeter and damage the voice coil. Do this on all sides of the tweeter (and also be patient, you don't need to separate it in one shot). Keep on doing it until one spot started separating then move on to the next spot. It may take a few minutes to complete the separation task but it is definitely doable. Good luck. :beerchug:
Click to expand...

Thank you. I left out the next most important question. How did you re-assemble it to ensure the coil is fitted perfectly into the gap. Figure I ask before you forget :)
 
Great job!

I'm also wondering how you make sure the coil is centered.

Did you also do the fluid in the 107's ?

My 107's sound great but I have not done the fluid. I'm mostly afraid of wrecking a tweeter that was working fine. The tweeters were clearly not ok in the case of your 105/3 Kefs, but I can't see myself successfully pounding a tweeter with a hammer and a knife.
 
@kwingylee In fact, KEF did a good job for SP1240. Normally tweeters will have alignment pins for centering the voice coil, but not this one. The only thing you need to do is to make sure the wires are positioned at the open notch and then use your fingers to center the voice coil by making sure the rounded edges for the upper and lower parts are aligned. I do have a recording of gluing the voice coil back into the magnet, but AK doesn't allow me to upload because the size is too big... :no:
 
@Shawnnnn Thx! I do have a pair of 107 Head Assembly which contains the T-33 tweeters. I redid the cabinet based on the LS3/5 specs for the head assembly and they sounded really nice. I will do the FF for T-33 at a later time. I think it should be a lot easier since they are much larger and not as fragile. If I have the time and get the T-33 done then I will create a new thread just for that. BTW, have you searched the forum? There could be others have already done so for their T-33s. :)
 
Randy Master said:
@kwingylee In fact, KEF did a good job for SP1240. Normally tweeters will have alignment pins for centering the voice coil, but not this one. The only thing you need to do is to make sure the wires are positioned at the open notch and then use your fingers to center the voice coil by making sure the rounded edges for the upper and lower parts are aligned. I do have a recording of gluing the voice coil back into the magnet, but AK doesn't allow me to upload because the size is too big... :no:
Click to expand...
Can you post the video on youtube?
 
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