Salbreth1
Active Member
KEF 103.2 budget crossover rebuild, completed
Hello guys,
So I made a big score at a local flea market last week and got this pair of Kef 103.2's for $50! Their in excellent condition including the grilles. Lucky me!
These were built from 1980-1985 according to kef. So after 30+ years the electrolytics are likely out of spec or worse. After some research, I also found a common problem with the caps in the S-stop circuit eroding the board.
My plan was to replace all of the electrolytic capacitors with metalized polypropylene films which wont deviate so much from their capacitance with frequency and temperature, and replace all the resistors with non inductive high tolerance wirewounds. all without going broke.
These drivers in these were matched to their crossovers for their target frequency response. I would't recommend changing the values of these parts. That said, the values were identical in each cabinet.
The original cans have a tolerance of 10% and resistors 5%.
For about $50, I was able to achieve this from available parts at digikey!
So first, The original crossovers have a center nut as well as double sided tape on each corner. Don't pull straight up or you may damage the board. Once the nut is off, carefully twist left and right to break the bond. then 2 nuts for the wires to the binding posts, spade connectors pull off for the LED, and I snipped the wires at the woofer and at the crimp connection to the tweeter. The woofers have different serial numbers and though the parts are identical , I would mark them so they go back into the same cabinet.
As you can see, there is erosion from the bad caps in the s-stop circuit. The trace was actually eaten away. After cleaning it, I pushed a thick resistor lead through the holes to make sure all the acid was out.
After checking all of the original parts, I found that most of them were within their tolerance range. Of course the leaking caps were shot, but both of the 1.5uf cap were about 150% out! Also both of the 7uf caps were just out of the 10% range.
The lead spacing on these parts was almost to good to be true. Everything seemed to fit snug with a little offset of the leads here and there. The 4.2uf cap was piggied with a 3.9uf, .22uf and .1uf to get me to 4.22uf and in tolerance. The 2 big 300uf cans are a 35hz high pass filter and were dead on when checked, so I left them alone.
I used the capacitor leads to repair the eaten traces and cleaned everything up with isopropyl alcohol, then added some new double sided tape.
I cleaned up the binding post connectors, and soldered the tweeters, getting rid or the crimp connectors
The dense foam was a pain. It catches on everything so readjusting the side foam is a must once its finally in. Be careful not to put tension on the wires to the tweeter. This only took a few hours, but will yield excellent results. I will let these settle over night with the radio on and do some critical listening tomorrow. stay tuned for the results!
Parts:
Nichicon XH series, PP films - 4pc. 10uf, 2pc. 7uf - $25
Panasonic ECW FA, PP films - 2pc. 3.9uf, 2pc. 1.5uf, 2pc. .22uf, 2pc. .1uf - $11.50
Vishay Dale ALVR wirewound resistors - 2pc. 12ohm 7w, 2pc. 1.5ohm 5w - $7.25
Ohmite 40 series wirewound resistors - 2pc. 680ohm 10w - $3.50
Ohmite WN series wirewound resistors - 2pc. 10ohm 5w - $3.25
Hello guys,
So I made a big score at a local flea market last week and got this pair of Kef 103.2's for $50! Their in excellent condition including the grilles. Lucky me!
These were built from 1980-1985 according to kef. So after 30+ years the electrolytics are likely out of spec or worse. After some research, I also found a common problem with the caps in the S-stop circuit eroding the board.
My plan was to replace all of the electrolytic capacitors with metalized polypropylene films which wont deviate so much from their capacitance with frequency and temperature, and replace all the resistors with non inductive high tolerance wirewounds. all without going broke.
These drivers in these were matched to their crossovers for their target frequency response. I would't recommend changing the values of these parts. That said, the values were identical in each cabinet.
The original cans have a tolerance of 10% and resistors 5%.
For about $50, I was able to achieve this from available parts at digikey!
So first, The original crossovers have a center nut as well as double sided tape on each corner. Don't pull straight up or you may damage the board. Once the nut is off, carefully twist left and right to break the bond. then 2 nuts for the wires to the binding posts, spade connectors pull off for the LED, and I snipped the wires at the woofer and at the crimp connection to the tweeter. The woofers have different serial numbers and though the parts are identical , I would mark them so they go back into the same cabinet.
As you can see, there is erosion from the bad caps in the s-stop circuit. The trace was actually eaten away. After cleaning it, I pushed a thick resistor lead through the holes to make sure all the acid was out.
After checking all of the original parts, I found that most of them were within their tolerance range. Of course the leaking caps were shot, but both of the 1.5uf cap were about 150% out! Also both of the 7uf caps were just out of the 10% range.
The lead spacing on these parts was almost to good to be true. Everything seemed to fit snug with a little offset of the leads here and there. The 4.2uf cap was piggied with a 3.9uf, .22uf and .1uf to get me to 4.22uf and in tolerance. The 2 big 300uf cans are a 35hz high pass filter and were dead on when checked, so I left them alone.
I used the capacitor leads to repair the eaten traces and cleaned everything up with isopropyl alcohol, then added some new double sided tape.
I cleaned up the binding post connectors, and soldered the tweeters, getting rid or the crimp connectors
The dense foam was a pain. It catches on everything so readjusting the side foam is a must once its finally in. Be careful not to put tension on the wires to the tweeter. This only took a few hours, but will yield excellent results. I will let these settle over night with the radio on and do some critical listening tomorrow. stay tuned for the results!
Parts:
Nichicon XH series, PP films - 4pc. 10uf, 2pc. 7uf - $25
Panasonic ECW FA, PP films - 2pc. 3.9uf, 2pc. 1.5uf, 2pc. .22uf, 2pc. .1uf - $11.50
Vishay Dale ALVR wirewound resistors - 2pc. 12ohm 7w, 2pc. 1.5ohm 5w - $7.25
Ohmite 40 series wirewound resistors - 2pc. 680ohm 10w - $3.50
Ohmite WN series wirewound resistors - 2pc. 10ohm 5w - $3.25
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