KEF 103.2 crossover upgrades

leesonic

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I thought it was time I did a write-up on my KEF 103.2 crossover upgrades. I think I'm on my third or forth one now. You can still buy the original Alcap capacitors from Falcon in the UK, but in my opinion it's not the best and/or only route to take.

Here is a picture of the stock crossover board. The relay (blue rectangle at the top in the middle) and the components to the right are for the S-STOP protection circuit. Lots of Alcap brand non-polarized electrolytics on the board, and all iron cored inductors. Those weird looking red things are merely encapsulated circuit boards for the protection circuitry.

KEF103-2crossovers01.jpg
This shows a close-up of the underside of the board, and where a lot of problems start with these speakers. The capactitors for the protection circuit leak, and corrode the PCB tracks underneath. I have actually seen crossovers where the tracks are totally rotten through, causing the woofer to appear dead.

KEF103-2crossovers02.jpg

Not only this, but look at the path the signals have to take. The "postive signal" (well, not really, because it's AC) has to go through a long track at the top of the board to the two 300uF caps. If this isn't bad enough, look at the path the "negative" signals have to take for the tweeter, all the way around the outisde of the board, just so it can pick up on the protection relay on the way. Note also that the tweeter is wired out-of-phase, as is the case with a lot of 12dB and higher crossover designs. The woofer "negative" signal doesn't go so far, but still has to go along a thin copper track, right by an area prone to corrosion by leaking capacitors.

KEF103-2crossovers03.jpg

Here is the board after I recapped it, I used film caps from Erse Audio, plus a couple of their non-polarized electrolytics. There is no real reason for using the Pulse-X (black) caps instead of the MET (yellow) ones, it just depends on what they had in stock. For the two 300uF caps right at the input of the crossover, I used two electrolytics with a 10uF film cap bypassing them.

I also re-routed some of the wiring. Instead of using the long track at the top to feed the two 300uF caps, I drilled the PCB and ran my input wire right here. I also drilled the board close to where the tweeter positive connection is (remember, tweeter is out-of-phase) and attached my input wire here, rather than go right around the board. Not immediately obvious from the picture, but I also ran a black jumper wire from this negative input to the negative woofer terminal, so the signal doesn't have to go through the copper trace.

Keen eyed viewers will notice this isn't the same board as in the first picture, but that's just how things turned out, I forgot to take pictures. You may also notice I removed the protection circuit at the request of the customer. All you have to do is remove all the protection components, and jump across the relay poles with a short piece of wire.

KEF103-2crossovers04.jpg

Here is another pair I did, the picture below shows the stock board.

KEF103-2crossovers05.jpg

Once again, extensive corrosion of the PCB tracks by leaking protection circuit capacitors (circled in yellow). In this case, the owner reported that the woofer stopped working completely.

KEF103-2crossovers06.jpg

Here is the completed crossover. As I said before, there is no real reason for using Pulse-X capacitors, this time Erse had all the values I needed in stock in the MET line of caps. Careful use of hot melt glue keeps everything together. I replaced the leaking caps on the protection circuitry with Nichicon FW series, just because that was what I had in stock at the time. You can see the black jumper wire more clearly for the woofer in this picture.

KEF103-2crossovers07.jpg

The underside of the board. I made good the broken PCB tracks using the lead-out wires from the protection circuit caps. You can see the link wire for the woofer negative, I also soldered the woofer positive directly to the back of the board.

KEF103-2crossovers08.jpg

Lee.
 
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Hi Lee. I just came across this post and thought that I would share my thoughts on the 103's that you recapped for me. I had posted this in another thread (KEF 103.2 Recap Question):

"I just picked up my walnut 103.2's from leesonic after he did a recap and fixed some traces that were lifting/shorted by a leaking cap and sitting
here now listening to them I can tell you that they sound spectacular. I've had these for about four years now and although I have considered
having them recapped due to the many recommendations here on AK, I didn't want to risk ruining their sound with a recap. I had read that KEF
matched caps within certain tolerances and didn't want to risk not being happy with the results. Well, I don't know if it was the recap or leesonic's
work or both but I'll tell you that they sound a lot better than before the recap and, they sounded great before the recap. Although they are still
every bit as wonderful and three dimensional as before and still retain all of the magic that I fell in love with in the first place, they sound more
lively with a definite improvement in the lower frequencies. The mids and high's seem to sparkle more (haha) and oh, what a sweet mid range it is.
I am not sure which caps Lee used but they retrain all of the sonic characteristics that appealed to me in the first place but with improvements all
around. Now I know what they must have sounded like when they were new and I wish that I would have had them recapped years ago."

Anyway, now I know what you replaced the caps with and I'll tell you that they just keep sounding better.
 
It is interesting to compare the schematics of the KEF 103.2 crossover with those of the Constructor Series CS3, which also uses a B200G woofer and T33 tweeter. The tweeter circuit has a slightly different shunt capacitor and resistor, but the other values are the same. The woofer circuit has the 300uF caps at the input on the 103.2 and at the woofer on the CS3. The CS5 design which has the above woofer and tweeter, plus a BD139 passive radiator, the crossover is exactly the same as the CS3.

The question is, which crossover sounds better? Having heard the 103.2s, I would be reluctant to buy the CS3 components just to find out. Now how about a 103.2 design, but in the larger enclosure of the CS5 with the passive radiator?

Lee.

KEF 103-2 crossover schematic.jpg

KEF CS3 crossover schematic.jpg
 
I'm not having any luck finding capacitors for my re-cap project...although honestly I haven't put in more than an hour's worth of work yet. I was set to order the exact list Lee had above, but the very first one I checked was out of stock. I emailed Erse to see if they would have stock anytime soon.

I've been emailing with Falcon Acoustics back and forth since March 2015 and have yet to be able to get any capacitors from them.

If anyone has a good source of capacitors, let me know! Would it be a big issue to go with poly caps throughout (just to maybe make it easier to find caps...Dayton, etc)? I'm new to this whole re-capping thing. It is appealing to not have to deal with future leaking electrolytics, but I don't want to compromise sound quality. I think my Kef 107's were rebuilt with a lot of poly caps. I've never heard another pair of 107's to compare, but mine sound good!
 
I picked up a pair of Kef 103.2s in April. I was powering them with 2 bridged NAD 2155 amps (150 WPC, 250 on program peaks). After a couple of hours of loud listening (easy listening music), I noticed a noise coming out of the right woofer. I tried flipping the speaker upside down and changing the amplifier, but the noise was still there. I'm guessing crossover issues? leesonic, I live in Northern NJ; do you offer repairs on Kefs? Thanks.
 
The speaker may have been damaged. Put the system in mono & swing the balance control. If the problem doesn't move from 1 spkr to the other, reverse the speakers. See if the problem persists. I really doubt this is a crossover issue, however rebuilding crossovers has become a fad on many forums.
 
I picked up a pair of Kef 103.2s in April. I was powering them with 2 bridged NAD 2155 amps (150 WPC, 250 on program peaks). After a couple of hours of loud listening (easy listening music), I noticed a noise coming out of the right woofer. I tried flipping the speaker upside down and changing the amplifier, but the noise was still there. I'm guessing crossover issues? leesonic, I live in Northern NJ; do you offer repairs on Kefs? Thanks.

If the noise you're hearing is sort of a faint buzz or distortion...sort of a light, static-y sound...for me...it was the crossover. An electrolytic leaked fluid and started eating away at the board. This has happened in both of my 103.2 speakers now. I would not have guessed it was the crossover...I was guessing the "woofer sag" issue. But repairing the crossover fixed it! Stupidly I only had the one speaker fixed, I didn't do the other one...two years later, the other one is having the same issue.

I am currently in process of re-capping, but having trouble finding capacitors (I'm new at this!). I checked the Erse website but they were out of stock on what i needed/wanted.
 
There's several other sites that carry audio grade NPE capacitors. But, one site never seems to carry all the values that I want. So, you usually have to mix and match, to get everything that's needed. Here's some of my go-to sources:

Bennics from Parts Express and Madisound.

https://www.parts-express.com/cat/non-polarized-electrolytic-capacitors/1385

https://www.madisoundspeakerstore.com/bennic-capacitors/

Mundorf E-Caps from Sonic Craft and Parts Connexion.

http://www.soniccraft.com/index.php/mundorf-ecap-ac-c-23_318_358

http://www.partsconnexion.com/capacitor_ele_mundorf_bipol.html

Hope this helps?
 
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There's several other sites that carry audio NPE capacitors. But, one site never seems to carry all the values that I need. So, you usually have to mix and match, to get everything that's needed. Here's some of my go-to sources:

Bennics from Parts Express and Madisound.

https://www.parts-express.com/cat/non-polarized-electrolytic-capacitors/1385

https://www.madisoundspeakerstore.com/bennic-capacitors/
Mundorf E-Caps from Sonic Craft and Parts Connexion.

http://www.soniccraft.com/index.php/mundorf-ecap-ac-c-23_318_358

http://www.partsconnexion.com/capacitor_ele_mundorf_bipol.html

Hope this helps?

I'll check that out, thanks very much!
 
I just checked the speaker again, only the right one has the background distortion, noticeable on quiet passages. I don't have balance controls on my Yamaha RXV1500, which I'm using as a pre amp to drive the NAD 2155s; when I just swapped the KEFs L&R, the noise followed the speaker. I'll swap the woofers next, but that's a soldering job and I don't have a couple of hours to mess with it right now.
 
I finished re-capping the four boards in a set of 105/3's. A total of 42 caps! Being cautious I contacted KEF of America and spoke with thei lead bench tech. I explained to him that I was typically measured caps that were 20+% out of tolerance. As opposed to replacing just the bad ones, he suggested a full recap, not with the polys that I wanted, but with good 10% or less electrolytic caps.

Respecting that I needed so many caps, I went with a bulk purchase from Erse & used their 5~6% tolerance electrolytic caps! I finished the recap and they sound much improved when tested and compared to an original board set.

Congrats on your successful re-cap. I see there are noted differences in our respectful re-caps, glad to know your method could be a viable option.
DC
 
Lee - I enjoyed reading your post, I have had 2 pairs of the 103.2's, gave one pair to good friend, now my other pair is suffering from crossover degradation. Almost no output from one speaker. I am wondering if you currently perform recaps for folks, and if so, could you be recruited to help with mine, or if not, could you recommend someone else?
Thank you for your consideration.
Tom White
 
Lee - I enjoyed reading your post, I have had 2 pairs of the 103.2's, gave one pair to good friend, now my other pair is suffering from crossover degradation. Almost no output from one speaker. I am wondering if you currently perform recaps for folks, and if so, could you be recruited to help with mine, or if not, could you recommend someone else?
Thank you for your consideration.
Tom White

Hey Tom, did you ever find someone to work on your speakers? I am in the middle of the same type of crossover restoration. Not too difficult, if you can solder. Luckily I have a "professional" solderer in my corner. We just completely re-capped my speakers, but the problem remains. I'm going to have to do the "circuit surgery"...repair the corroded traces in the board.
 
I just finished with my second sets of 103/5 crossovers. It a task that demands a lot of attention to say the least. If I can help let me know as well. The 4 boards per set had custom cut and made to fit KEF's particular caps, so if you end up using another cap brand, like the 5% Erse 'lytics, you probably will have to get a bit creative with your cap mounting exercises!

The sonic difference is starling! Erse makes some excellent grade 5% caps and a lot more. The bad news is you have to buy in quantity to make it worth their wild. I would suggest going in with a buddles to get the order minimum. Should not be too hard with needing 42 caps to do all 4 boards. Another thing is their shelf stock may be limited too. Be prepared to double up a size or two yo get close to the value needed. The smaller values you can find in their Poly brand caps as well and Parts Express has 10% grade caps that are "OK" too.
DC
 
Or you could just have Lee do it. As you have probably have figured out, he is an expert. My speakers have been performing flawlessly since getting them back. The big three dimensional sound still surprises me sometimes. I also have one of Lee's NAD 3020's and it too has performed flawlessly over the past year.
 
I am available to do crossover work. I just have a backlog of work right now, but I can get them done if you want/need them doing.

Lee.
 
Just wanted to report back that the KEF 103.2's are now fully functional! Did a full re-cap, then repaired the broken/corroded traces on the PCB's. They sound great now. Well worth a few hours of work. Happy that I have a "pro" in my corner to do the soldering...my mom has built airplane boards for 30-40 years now...not that I think I COULDN'T have done the soldering myself, but she sure made it look easy and got it done in no time. Lee's posts were quite helpful in just helping to confirm exactly "what" we were fixing.
 
Hi Guys,

I've recently bought a recap kit from Falcon Acoustics. I also have a resistor that is heavily corroded (R9). Unfortunately the resistor cannot be read anymore on either crossover. The 1st picture posted by Leesonic Shows it as a 1.5Ohm 2w resistor, the schematic I've located here says its a 2.2Ohm resistor. I cant confirm it as neither physically look the same.

http://audiokarma.org/forums/index.php?threads/kef-103-2-recap-question.576578/

The black circular one highlighted in the middle of the crossover below (posted here by Leesonic) looks right, can anybody check the value of it for me? I've been looking for weeks for this and it would be so helpful!

upload_2017-2-5_20-0-5.png

Heres the thread I started on it a couple weeks ago if you guys need any more clarification or details,

http://audiokarma.org/forums/index.php?threads/kef-103-2-recap-question.753379/#post-10257380

Thanks!

Matt
 
I just completed a recap of the crossovers in my 103.2's and I have a question about the crossover circuit. I ordered parts from Erse, and I am kicking myself for not ordering a couple of extra capacitors. The question I have is about the 2.2 uF cap in the tweeter portion of the circuit. The crossovers in my 103.2's, which are SP2011A models, had 1.5 uF caps in those positions, so that was what I ordered for replacements. However, on pulling the old ones out, they actually both measured at 2.08 uF, closer to the 2.2 uf value in the circuit diagram posted. The new caps in my setup measure at 1.50 uF. Can someone explain what effect this would have on the circuit and/or sound characteristics of the speakers? I did some digging on google, but this crossover design is a bit more complicated than the simple examples I found explanations on...

While the speakers appeared to be working well before the change out of parts, there was some leakage and circuit damage on the board of one of the speakers from the little caps in the protection circuit. The blue Allcap caps all looked OK and measured out OK, but they were all replaced, in addition to the three polarized caps in the protection circuit.
 
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