KEF 103.2 rebuild

[Eppie]

@Mark Caudill One more note. I did some research and there are several different versions of the crossover for the 103.2. I found the schematics for the SP1144 but mine, for example, are the SP1121. Keep that in mind if sourcing parts or replacement crossovers. Also, some crossovers were installed with military strength 3M two sided tape. If your boards are held down with tape, remove them very carefully as the tape can be surprisingly strong.

 

[Eppie]

I didn't see this thread until a few minutes ago, but I have to comment on "crappy binding posts". Those are absolutely fine and are easy enough to use, as you know how- a hex socket will fit onto the red and black nuts, so that's no big deal. They were also made to accept banana pugs that were paired in a piece of plastic so the wires could be connected in one motion, rather than using all metal plugs that can touch. They're still available in that configuration and until the marketing BS storm of the '80s, this type (not the ones in the photo) were the standard unless they were used to connect equipment that didn't have pairs.


View attachment 60154

I did make a pair cables with banana plugs which I included with the speakers. Bare wires were a PITA.

 

[highfigh]

I did make a pair cables with banana plugs which I included with the speakers. Bare wires were a PITA.

Get skinnier fingers.

 

[TLS Guy]

@Mark Caudill One more note. I did some research and there are several different versions of the crossover for the 103.2. I found the schematics for the SP1144 but mine, for example, are the SP1121. Keep that in mind if sourcing parts or replacement crossovers. Also, some crossovers were installed with military strength 3M two sided tape. If your boards are held down with tape, remove them very carefully as the tape can be surprisingly strong.

I could not find a crossover schematic either. A wide flat blade does less damage to the woodwork, as it is wider. They bend a bit, and above all, are wider. So that means less pounds per square inch on the wood, and less damage.

If all else fails, you can drill a hole in the back, opposite the magnet, and pass a brass drift through onto the magnet and rap it hard with a hammer, best to use a large soft impact hammer. I have a very nice collection of brass drifts. They have persuaded a lot of obstinate objects to shift over the years without doing damage.

 

[highfigh]

I could not find a crossover schematic either. A wide flat blade does less damage to the woodwork, as it is wider. They bend a bit, and above all, are wider. So that means less pounds per square inch on the wood, and less damage.

If all else fails, you can drill a hole in the back, opposite the magnet, and pass a brass drift through onto the magnet and rap it hard with a hammer, best to use a large soft impact hammer. I have a very nice collection of brass drifts. They have persuaded a lot of obstinate objects to shift over the years without doing damage.

You want him to hit a ceramic magnet with a brass drift and hammer? This isn't a wheel bearing race, it's a speaker frame that's made of stamped steel. A couple of woodworking clamps and a caul pressing on a large dowel would be a much better method, as long as it's not just cranked until it comes out.

Also, using a straight/flat tool to press against a round edge isn't a great way to do this without leaving marks.

This is a tricky repair- heat might help, but too much will cause the surround to become loose, or worse. Patience will be the best tool for this.

 

[cpp]

I could not find a crossover schematic either. A wide flat blade does less damage to the woodwork, as it is wider. They bend a bit, and above all, are wider. So that means less pounds per square inch on the wood, and less damage.

If all else fails, you can drill a hole in the back, opposite the magnet, and pass a brass drift through onto the magnet and rap it hard with a hammer, best to use a large soft impact hammer. I have a very nice collection of brass drifts. They have persuaded a lot of obstinate objects to shift over the years without doing damage.

On another forum of a guy doing some updates. He got his crossover diagram from the KEF Tech team for the 103.2. I haven't looked it over.

 

[MrBoat]

Never saw this thread before today. Hat's off to a job well done. That had to be a satisfying repair to do.

 

[TLS Guy]

You want him to hit a ceramic magnet with a brass drift and hammer? This isn't a wheel bearing race, it's a speaker frame that's made of stamped steel. A couple of woodworking clamps and a caul pressing on a large dowel would be a much better method, as long as it's not just cranked until it comes out.

Also, using a straight/flat tool to press against a round edge isn't a great way to do this without leaving marks.

This is a tricky repair- heat might help, but too much will cause the surround to become loose, or worse. Patience will be the best tool for this.

If you use brass drifts and a good quality soft impact hammer you can get a lot of obstinately stuck delicate machinery apart without doing damage. My brass drift set is one of my most prized possessions in my tool chest. It would do no damage to that magnet.

 

[highfigh]

If you use brass drifts and a good quality soft impact hammer you can get a lot of obstinately stuck delicate machinery apart without doing damage. My brass drift set is one of my most prized possessions in my tool chest. It would do no damage to that magnet.

Well aware- I'm also a boat mechanic and if you have worked on boats, you know how stubborn some of thier parts can be. I just don't like the idea of striking speaker magnets.

One question I would ask before assuming that no harm would come to the magnet- how is it attached to the frame? If it's bolted on, I would be less hesitant, but I still might be inclined to use some kind of press. This probably comes from having serviced speakers for customers and it's a bit like the medical profession- at least do no harm. Better to take more time than break something that would be very difficult to replace or repair.

Want to show the drifts? I'm a bit of a tool addict, myself.

 

[TLS Guy]

Well aware- I'm also a boat mechanic and if you have worked on boats, you know how stubborn some of thier parts can be. I just don't like the idea of striking speaker magnets.

One question I would ask before assuming that no harm would come to the magnet- how is it attached to the frame? If it's bolted on, I would be less hesitant, but I still might be inclined to use some kind of press. This probably comes from having serviced speakers for customers and it's a bit like the medical profession- at least do no harm. Better to take more time than break something that would be very difficult to replace or repair.

Want to show the drifts? I'm a bit of a tool addict, myself.

I will get around to photographing them when I get time. Those magnets are screwed on. If there is a chance of doing serious damage to the front of the cabinet, I would follow my plan. Brass drifts are totally different from steel ones. I think it is because it is springy and compressible. Together with a really good well designed sift impact hammer you can free up stuff you would not think you could without causing damage.

 

[TLS Guy]

On another forum of a guy doing some updates. He got his crossover diagram from the KEF Tech team for the 103.2. I haven't looked it over.

View attachment 60176

That circuit is interesting. It is second order low pass and third order high pass, with the Q of the filter modified by R2. I can see some of Raymond Cooke's impedance compensation at work here. The protection is from C2 and C3, C2 largely. This type of circuit was common back then to protect the bass driver from amp DC off set. There were quite a few amps that did not have DC offset protection from output transistor failure, back then.

I would advise removal of C2 and C3. Connect the R3 L1 connection to the +ve speaker terminal. B & W used to do this back then, and those caps used to fail. I bet that is what has happened to the OP's speaker. The speaker will sound better with those caps removed. They negatively affect the sound.

 

[Eppie]

That circuit is interesting. It is second order low pass and third order high pass, with the Q of the filter modified by R2. I can see some of Raymond Cooke's impedance compensation at work here. The protection is from C2 and C3, C2 largely. This type of circuit was common back then to protect the bass driver from amp DC off set. There were quite a few amps that did not have DC offset protection from output transistor failure, back then.

I would advise removal of C2 and C3. Connect the R3 L1 connection to the +ve speaker terminal. B & W used to do this back then, and those caps used to fail. I bet that is what has happened to the OP's speaker. The speaker will sound better with those caps removed. They negatively affect the sound.

That's different from the schematic I found for the SP1144 on this website. It's not provided by KEF though and was hand drawn. I have yet to find a schematic for the protection circuit.

 

[Eppie]

Never saw this thread before today. Hat's off to a job well done. That had to be a satisfying repair to do.

Thanks Boat! I had one major gaff. A review on the 103.2 said the veneer was walnut, so I purchased some, not doing more thorough research. When I brought it home I knew the species was different. Some more digging and I learned that there were 3 veneer options. I'm pretty sure these were teak. Had to play with the stain and oil to match it up so that it would not be obvious. Could not get teak veneer locally any way. The top seemed to blend in ok in the end. My daughter better not sell these. If she wants something different I want them back.

 

[TLS Guy]

That's different from the schematic I found for the SP1144 on this website. It's not provided by KEF though and was hand drawn. I have yet to find a schematic for the protection circuit.
View attachment 60191

The protection circuit on that Schematic are the two 30 mfd. caps C2 and C3. That circuit also involves the high pass crossover, which is redundant as and high pass circuit will not pass DC. The caps are the protection, but I suspect there was some type of device that was probably a relay shunting those caps to disconnect when those caps were charged and then slowly discharged them though the light. That would cause an auto reset of the protection circuit. The DC protection is C2 and C3 in both circuits, and that is the essence of the protection. I don't think the protection was for audio overload, but for DC offset protection. That was common in that era.

 

[Eppie]

The protection circuit on that Schematic are the two 30 mfd. caps C2 and C3. That circuit also involves the high pass crossover, which is redundant as and high pass circuit will not pass DC. The caps are the protection, but I suspect there was some type of device that was probably a relay shunting those caps to disconnect when those caps were charged and then slowly discharged them though the light. That would cause an auto reset of the protection circuit. The DC protection is C2 and C3 in both circuits, and that is the essence of the protection. I don't think the protection was for audio overload, but for DC offset protection. That was common in that era.

Advertising and KEF archive pages say that it was for overload protection, although it could have been intended to protect from DC offset as well. On my crossovers there were four 150mfd caps next to the relay. I regret not taking the time to make a schematic while I had the crossovers out. If I replace the caps down the road I'll be sure to make a proper schematic next time and post it.

 

[TLS Guy]

Advertising and KEF archive pages say that it was for overload protection, although it could have been intended to protect from DC offset as well. On my crossovers there were four 150mfd caps next to the relay. I regret not taking the time to make a schematic while I had the crossovers out. If I replace the caps down the road I'll be sure to make a proper schematic next time and post it.

As I think about it, your handwritten circuit is likely correct, as a peak voltage sensing relay with the caps on the front end, would allow for a peaking relay circuit to protect against DC pass through and peak signal overload. The bulb would cause auto reset in either circumstance.

 

[highfigh]

I will get around to photographing them when I get time. Those magnets are screwed on. If there is a chance of doing serious damage to the front of the cabinet, I would follow my plan. Brass drifts are totally different from steel ones. I think it is because it is springy and compressible. Together with a really good well designed sift impact hammer you can free up stuff you would not think you could without causing damage.

Brass is softer and while it's being hit, it has some elasticity, but it goes back to its original shape unless, as many have found, it's hit with something much harder and then, it won't return. I don't know how many pieces of soft brass that were used as a drift by hitting it with a steel hammer and the ends mushroomed.

You're referring to using a dead blow, the type filled with lead or something else that doesn't recoil? I would agree that one of those would be a good choice. That arrangement would provide a good impact, but it loses some of the energy due to the materials. I have been watching YouTube videos by a musical instrument repairman and he shows how he repairs all kinds of damaged horns and some of them look as if they were thrown down a set of stairs, then stepped on. He uses metal rods to expand & straighten the narrower sections, then steel balls mounted on the end, to remove dents. On larger diameter curved sections and tuning slides, he uses steel balls of different sizes and what looks like a mallet, but the end has several large rare earth magnets and it acts like an English wheel without the outer roller.

 

[TLS Guy]

Well aware- I'm also a boat mechanic and if you have worked on boats, you know how stubborn some of thier parts can be. I just don't like the idea of striking speaker magnets.

One question I would ask before assuming that no harm would come to the magnet- how is it attached to the frame? If it's bolted on, I would be less hesitant, but I still might be inclined to use some kind of press. This probably comes from having serviced speakers for customers and it's a bit like the medical profession- at least do no harm. Better to take more time than break something that would be very difficult to replace or repair.

Want to show the drifts? I'm a bit of a tool addict, myself.

Here is the picture you wanted. This is my brass drift set and soft impulse hammer. The head of the hammer is full of small steel beads.

 

[highfigh]

Here is the picture you wanted. This is my brass drift set and soft impulse hammer. The head of the hammer is full of small steel beads.

I have several brass and steel drifts that I got from my dad and I have a dead blow mallet that looks the same as yours- I have several, for different jobs. Sometimes, it doesn't need to be so large and I have a few hammers with plastic & hard rubber heads, one with a brass head and several steel hammers.

As my tool variety grows, I sometimes think about when I didn't have many and how difficult various repairs and tasks were.......

 

[Eppie]

I have several brass and steel drifts that I got from my dad and I have a dead blow mallet that looks the same as yours- I have several, for different jobs. Sometimes, it doesn't need to be so large and I have a few hammers with plastic & hard rubber heads, one with a brass head and several steel hammers.

As my tool variety grows, I sometimes think about when I didn't have many and how difficult various repairs and tasks were.......

As my dad passed away early due to cancer I really cherish the tools I inherited. He was a master organ builder by trade so learned to do wood work and sheet metal. When we moved to Canada he joined a German organ builder who was a very good businessman. As organs went electronic, the company transitioned to a tool and die shop and small manufacturing. My dad became a capable machinist and millwright over the years and the company was one of the first to invest heavily in CNC equipement. MIkado463 might be interested to know that the company also built and tested throttle control systems for GM diesel locomotives.

I inherited some woodworking tools which I shared with my brother, but I received the bulk of the machinist tools, including some Mitutoyo measurement and setup equipment. I don't have room for a lathe but a table top clock makers lathe would be very cool to have for machining brass parts. My grandfather was also a master organ builder and I have a few of his tools as well. (The lathe isn't mine but a good example.)