Kef 105/3 crossover

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hello I have a pair of these speakers and have been reading about people replacing the capacitors due to ageing. I have had a quick look inside my cabinets and the caps look fine i.e not swollen, but I have read that they dry out. If it is advisable to replace them, what caps would any one recommend? I have a schematic of the crossovers and there a total of 23 caps per speaker :eek: The values on my schematic are as follows;(value times total)
240 x 2
100 x 7
80 x 4
60 x 1
50 x 3
20 x 3
15 x 1
7 x 2

Any advise would be greatly appreciated, I think these are fantastic speakers and about 18 months ago all the bass units were re-foamed complete with new centre doughnuts so they should be okay for the future...I hope. I know Kef do not have any more drivers for this model now, that is why I am asking if it would be worth all this extra work and would I notice any improvement? thinking along the lines if it ain't broke etc...

Cheers
 
Hello sbx, I have just joined the diyaudio group so forgive me if I am over stepping boundaries. I too have just acquired a set of 105/3's and I have just had the bass units re-coned. My problem is that it appears I am missing the highs from one side. I swapped the speaker wires to eliminate the source and then opened up the cabinet. No swollen capacitors or apparent open circuits but one of the capacitors has lost its plastic identification cover. On closer examination the capacitor was leaning (incontact) with what looks like a ceramic block resistor. Between them was some of what was left of the capacitor cover (somewhat melted and discoloured). All this to ask where can I get a copy of the schematic for the board and does anyone have a simple test to check the function of the board and I'm assuming the tweeter?

Toolman
 
sbx,

as there are so many capacitors, and a lot are high capacitance values, it is going to be expensive to replace them all with new high quality,
long life capacitors.

I you are able to Post the Schematic of the crossover, I will advise you which ones are the most critical to spend money on,
and which ones will be OK to replace with lower price caps.
Either the KEF printed schematic, or your own hand-drawn, will be OK,
but do show which cap values are where, and show all inductors' and resistors' positions, and the connection points for the drivers.

*****************************************************************

Toolman,

I'll comment more on yours after we see what sbx can Post here,
though you can look in the other 105/3 at its crossover to see what is printed on the equivalent position cap there
-the one which corresponds to the burnt cap in the missing highs' 105/3 - and Post that information here.
The melted cap has likely gone Open-Circuit and is no longer passing signal.
 
Last edited:
Alan, and Inductor, thank you for the information. I have done a bit of testing and determined that the tweeter isn't working. (applied signal directly and no output). I then applied signal to the HF board and there is output. The cpa may not be toast but I will replace it any way as it has been exposed to excessive heat anyway. I include a photo of the board in question.
 

Attachments

  • DSC_0716.jpg
    DSC_0716.jpg
    423 KB · Views: 1,328
Toolman, when using components (new) for repairs, always make it with a new matching pair and repair the other speaker too for a perfect match in sound output. Unless it's the same exact component/tolerance. (As someone said before, there are exceptions, like a pair of speakers fine-tunned different from each other to achieve for the same result/sound footprint).
 
Last edited:
KEF 105/3 crossover

Inductor, good point ref the balance of new components. I note as well that the schematic you directed me to shows the capacitor in question to be 15 mfd, the one on my board (and confirmed on the other cabinet) is a 16 mfd.
As I have eliminated the board as the source of no output I now have to figure out how to separate the tweeter from the woofer without causing further damage. There is a nut in the top but when I turn it so too does the whole tweeter. Any thoughts.
 
send to KEF

Toolman,

my uniQ drivers are later models than those in the 105/3,
however they also have a screw on the back.
I haven't turned it because the drivers are working well,
though I think it is possible the inner tweeter section unscrews.
Safest is to send the entire driver to the authorized KEF service centre in your country ...
{and not simply to a KEF selling shop's technician - beware, some ruin complicated components}.
Look under:- KEF Global for service details, or email to them.

I'll Post more about that crossover when I have time available - hopefully soon.
 
Toolman,

my uniQ drivers are later models than those in the 105/3,
however they also have a screw on the back.
I haven't turned it because the drivers are working well,
though I think it is possible the inner tweeter section unscrews.
Safest is to send the entire driver to the authorized KEF service centre in your country ...
{and not simply to a KEF selling shop's technician - beware, some ruin complicated components}.
Look under:- KEF Global for service details, or email to them.

I'll Post more about that crossover when I have time available - hopefully soon.

Hi Alan, I have bought some of the later 4th generation UniQ from Kef purely as back up for the future, I know what you mean about the slightly different fitting, a friend of mine replaced his last year and came across this issue, which he has successfully worked around :)

Cheers for the reply(I am in the UK BTW and dealt direct with Kef support who offer a very good service)

All the best
 
Thank you both (Alan and sbx) for the info. I figured out how to remove the tweeter from the driver. Once the back cover is off the driver hold what looks like a large nylon washer in the center back and then remove the single screw. Next de-solder the black and red lead from the side connector. Lastly push the nut (that the screw came out of) straight out and the tweeter and leads come out. In my situation one of the leads had come detached I have re-soldered and it appears to work. I still have to do some testing to ensure the board doesn't have any other bad components. I have replaced the 16 mfd 50v 10 % ALCAP capacitor with an MKP 16 mfd 250v 5%.
 
Hello I have a pair of these speakers and have been reading about people replacing the capacitors due to ageing. I have had a quick look inside my cabinets and the caps look fine i.e not swollen, but I have read that they dry out. If it is advisable to replace them, what caps would any one recommend?

Cheers

Not to rain on anyones parade but be aware that KEF Reference Series models achieved high matching within a pair by "customizing" each crossover to the drivers used.

I worked as an engineer in the Maidstone factory in the early 80's. The practice was to buy fairly wide tolerance capacitors, sort them into a number of tight groups and then match up each group with slightly different value inductors. That means that any crossover schematic is likely to be slightly at odds with the values you see on your circuit board, and the values on the capacitors may be the nominal value while the exact value was chosen to be off nominal!

It might be a good time to leave well enough alone, unless you had a good reason to believe that capacitors had degraded. I think the best advice would be to unsolder one end of each cap and measure its value. If it has a value within the printed tolerance on the cap then you are better off leaving it alone rather than replacing with an exact nominal capacitor. New close tolerance capacitors will actually degrade the pair matching.

David
 
Not to rain on anyones parade but be aware that KEF Reference Series models achieved high matching within a pair by "customizing" each crossover to the drivers used.

I worked as an engineer in the Maidstone factory in the early 80's. The practice was to buy fairly wide tolerance capacitors, sort them into a number of tight groups and then match up each group with slightly different value inductors. That means that any crossover schematic is likely to be slightly at odds with the values you see on your circuit board, and the values on the capacitors may be the nominal value while the exact value was chosen to be off nominal!

It might be a good time to leave well enough alone, unless you had a good reason to believe that capacitors had degraded. I think the best advice would be to unsolder one end of each cap and measure its value. If it has a value within the printed tolerance on the cap then you are better off leaving it alone rather than replacing with an exact nominal capacitor. New close tolerance capacitors will actually degrade the pair matching.

David

Hi David, cheers for the info, I had read something similar somewhere else but was not too sure until now, its good to hear info like this from someone who has actually worked with this kit. I am happy with the way my pair perform but was just exploring the possibilities if I decided to refurb the cabinets. I have purchased a pair of the 4th generation Uni Q from Kef as an advised upgrade, I thought they might be getting scarce but when I ordered them I was informed there were still over a 100 in stock :confused:, I haven't fitted them yet. Will new tweeters have any bearing on the matching? Saying that,mine have very slightly different serial numbers on the back so I don't know if they were a true matched pair, there are two very old black labels on top of the white label stating 18697a and 18897b which could have been a mis print or some else has tried to make them look like a matched pair. I would find it strange if they weren't because where would one cabinet come from?

Anyway thanks for your input

All the best
 
The pair matching and crossover adjustment only pertained to the Reference Series systems. They would build drivers in batches of 96 units and let the computer sort through and find the best 48 pairs. Then 48 woofer pairs would be linked up to 48 tweeter pairs, based on sensitivity, etc. Crossover capacitors would be balalnced against inductors as I described before.

If you blew a tweeter then they could send you a second one matched to its mate, by pulling up the record of the one you still had and sorting it through a batch again. I think after a couple of years they found the process too tedious though and started sending out middle-of-the-batch universal replacement tweeters.

Replacing tweeters with new ones will effect exact pair matching, but really, when a product is over 20 years old, its just nice if it plays!

Enjoy,
David
 
And here are the characteristics of the woofers and the official xover schematics.

Still looking for the same for the other drivers. Will keep you posted.

And here is a site that carries the components used in the filters and a lot of information on them:
Audio Grade Electronic Components for Loudspeakers
 

Attachments

  • bass.PNG
    bass.PNG
    687.1 KB · Views: 303
  • b200-sp1014.gif
    b200-sp1014.gif
    50.1 KB · Views: 275
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.