Substituting KEF Uni Q Drivers

[tothehilt]

I am wondering how detrimental to the sound it would be to substitute a B160 SP1322, from a Q30 for the B160 SP1345 in my KEF Reference Model 2. they have different tweeters, NT 19 and NT25, respectively. Would the substitution discombobulate the crossover? Is this something that can only be determined by trial, or is there a way to predict the outcome?

[a_tewinkel]

You'll have to measure. There's really no way to know how it will turn out. Most probably the crossover will have to be modified.

[AndrewT]

I thought the Uni Q range, all had the crossover mounted directly on the back of the driver.

[tothehilt]

"I thought the Uni Q range, all had the crossover mounted directly on the back of the driver."
Not on my Model twelve, its right behind the binding posts, very easy access compared to the 104/2 which are a bear. I don't know about any others.

[tothehilt]

"You'll have to measure. There's really no way to know how it will turn out. Most probably the crossover will have to be modified."

I was afraid of that, I think I am going to give it a try, as the voice coil on one of mine is stuck and replacements are not east to find. Going to take it to my local repair shop today to see how feasible a repair is, but I am not hopeful.

[tothehilt]

So I visited the local stereo repair shop. The fellow there told me it would cost about $150 to repair the voice coil on the driver, then he upped it to $250 when he realized there was a tweeter installed in the middle of the midrange. Turns out the tweeter is easily removed, one screw and an easy desolder. I could buy the Uni Q drivers up for auction on Ebay right now and replace the tweeters in them (NT19) with the Model 2 tweeter (NT25) and basically, I think, have the same thing as the midrange is the same on both. However, I decided to take the magnet off the driver and look at the VC. Nothing to lose right?

Paint thinner and a razor blade did the trick. Next step will be to straighten all the bent copper wires and the foil surrounding them.

Somewhat tedious but doable. The final, and trickiest part, will be to get the magnet positioned back onto the VC. Here is a link to a jig someone made for that purpose.
As promised Pics of the magnet Jig - AudioKarma.org Home Audio Stereo Discussion Forums
I am hoping I can get away with just the PVC pipe and a dowel.

The Uni Q drivers go off today. Hopefully I am not missing my chance at an easy repair, after finding out that the VC repair is more difficult than I thought.

[phivates]

You have what I have. Except I have no hope of succeeding at this enterprise. So the Q70s I got for fifty bucks will end up costing a bit more. I have wanted a uni-q set for some time so I got what I wished for, plus a little something extra, as usual. I may try planting my Fostex 6.5 coaxes in place of the kef mid-tweet if the crossover is easy to sort. Probably not.

Edit: the 19 and 25 tweeters must be different sizes, no?

[tothehilt]

Don't give up untill you make a thorough search of Ebay. I passed on a pair of UniQ drivers because i wanted to do this myself, but there were more than one. I would think any driver with a B160 midrange would work.

As for fixing them yourself, they are easier than most as there is no need to disconnect the voice coil, surround, etc., since the tweeter screws right out. If you can bend the wires back in shape the main thing is to make a jig to place the magnet back in correctly. I finally hit upon the idea of screwing the magnet to a wood plank, and then screwing the driver to another plank. then with the 4 screws that hold the driver to the plank I can slowly lower it into the proper alignment.

My T25 is 1 10/32" diameter at the base. what is the T19?

[phivates]

I measured 1 7/32nds at the base so hopefully the two will interchange. I have to say these latter day KEFs are not so impressive once the coaxial configuration is set aside. Nothing special cabinet wise, but then they were only 1200/pair in the mid 90s. I'm guessing they invited being overdriven, meaning overheated, thus our separated voice coils. Stamped baskets, electrolytic caps, chipboard...ordinary.