Kef KM1 in need of repair.
- Thread starter James46
- Start date
Paul Marchant
pfm Member
And this week's update...
I've been over to the lockup where the bass cabs are languishing, and gently caressed my cones (ahem).
Two only slightly rub now, a considerable improvement from last week. The third appears to have completely fixed itself.
Another couple of weeks, and I reckon it'll be time to get everything together once more and run them up.
I've been over to the lockup where the bass cabs are languishing, and gently caressed my cones (ahem).
Two only slightly rub now, a considerable improvement from last week. The third appears to have completely fixed itself.
Another couple of weeks, and I reckon it'll be time to get everything together once more and run them up.
foxwelljsly
Me too, I ate one sour too.
These are, without a doubt, the most extraordinary items I have ever seen resuscitated on a thread here. Amazing. I can only imagine the thunder they will be capable of.
Paul Marchant
pfm Member
I've once again visited the lockup where the LF enclosures are living and tickled my transducers (ahem).
Some improvement has been noted over last week. There's less rub on the two that haven't yet fixed themselves, but not a big change. The third one appears fine.
Soon....
Some improvement has been noted over last week. There's less rub on the two that haven't yet fixed themselves, but not a big change. The third one appears fine.
Soon....
Paul Marchant
pfm Member
And this week's predictable update...
I've gone over to the lockup where the bass enclosures are hiding, and manipulated their moving parts (ahem).
Some further progress is apparent. Of the two that rubbed last week, one now only rubs at the extreme of its excursion and appears OK if just tickled gently. The other still has rub at all points in its movement range.
We're getting there gradually...
I've gone over to the lockup where the bass enclosures are hiding, and manipulated their moving parts (ahem).
Some further progress is apparent. Of the two that rubbed last week, one now only rubs at the extreme of its excursion and appears OK if just tickled gently. The other still has rub at all points in its movement range.
We're getting there gradually...
Paul Marchant
pfm Member
I bought it, and it's slowly working it's way from the USA to me.
It was an awful lot of money for what it is, but there are schematics shown in the auction pictures for the filter circuits in the crossover. They're not present in either of the two scanned copies of the manual that I've acquired so far. Would I ever need them? Probably not, in that if I had a failure in that part of the circuit on one of the amps it's the sort of electronics repair that I'm good at (am PCB repair guy for a living) and I'm pretty sure I could fix it without the schematic, but rather than tempt fate it'd be easier to have that information.
I've been watching that listing for a few months, and had decided that if and when I got the KM1s to working condition I'd pay the money and buy it. I'm more-or-less there now and eventually yielded and haggled him down in price a bit.
Paul Marchant
pfm Member
I didn't get a chance to visit the lock-up this week, too busy at work.
When I had the bass cabs out, a few weeks ago, I noticed that one of the grilles was slightly warped and wouldn't clip all the way into the body of the loudspeaker.
Knowing nothing at all about remedial woodworking, I've brought it home and laid it on the kitchen table with some 3/4" drive sockets as weights in an attempt to straighten it.
No idea if it'll work, but if not I can make a replacement grille. We'll see what comes over the next week.
When I had the bass cabs out, a few weeks ago, I noticed that one of the grilles was slightly warped and wouldn't clip all the way into the body of the loudspeaker.
Knowing nothing at all about remedial woodworking, I've brought it home and laid it on the kitchen table with some 3/4" drive sockets as weights in an attempt to straighten it.
No idea if it'll work, but if not I can make a replacement grille. We'll see what comes over the next week.
Hi Paul,
I've just stumbled over your thread, fascinating that a pair of KM1s have survived and are in good hands! I worked in R&D at KEF during my university holidays in 1983/84, and in the summer of '84 I was the KM1 production line. I assembled the first 10 production units or so, IIRC 4 went to the BBC and the rest to rich arabs.
I recall lifting a pair into the upstairs demonstration room - they were a 4-man lift - I stayed on after work when the factory was quiet, and listened to them until my ears fell off - I briefly compared whatever the current best CD player was at that time (Meridian's first 14 bit player, Philips based??) with a Sondek, but the speakers volume and hence dynamic range made the vinyl sound compressed vs CD, so I worked my way through the entire CD collection.
Laurie Fincham was Kef's R&D director at the time, now at THX apparently, and has some youtube content out which I must look at!, and Rick Ciccone plus a Canadian guy whose name I don't recall were the project team, with me on assembly duties. Kef did the cabinets and drivers, any electronics issues the amps were pretty much standard Quad 405s IIRC. We matched the drive units carefully (as was common practice at KEF), there was a 10mx10mx10m measuring room where the drivers went through individually, then a mini computer did an FFT analysis on the output produced by a 'click' input (delta function) and the results were sorted into matched pairs for response & sensitivity.
I've seen a couple of inaccuracies in various sources that are worth mentioning - the bass drivers were individually driven by their own 405, not bridged as some sources say. The midranges likewise were driven directly, and just the tweeter was bridged - so 8x 405s total in spite of what the science museum website says! (but you'll know that..) The tweeter was ferro fluid cooled, not the midranges - and we had some problems in testing that when the tweeters were driven too hard, the ferrofluid pissed out and overcooked the voice coils. I think the tweeter 405s were down-specced power-wise as a result.
I assembled the tweeter/ midranges in their little wooden box, which was damped inside with polyol (sp?), then they got tested again before the box got bolted into the internal frame that carried the electronics, with the bass boxes bolted on either side.
I got the gig at Kef having worked holidays previously at Boothroyd Stuart/ Meridian - Bob Stuart put me in touch with Laurie. Meridian used pretty much wall to wall KEF drivers, and it wouldn't surprise me in the least if Bob had some input on the KM1 design - not least the crossovers. Bear in mind this was KEFs first active speaker, and Meridian had been doing the M2 & M3s for a while (I still have a pair of both. M3s still in use!)
I'll be watching your thread with interest - all the very best on getting them going again! I'm not sure I can be of any use in the rebuild - it was so long ago, and I was both junior and part-time - but feel free to pm me if I can help. I'll try to find the couple of photos I have of a brand new one on the shop floor at the Tovil factory....
regards and best of luck!
Martin
I've just stumbled over your thread, fascinating that a pair of KM1s have survived and are in good hands! I worked in R&D at KEF during my university holidays in 1983/84, and in the summer of '84 I was the KM1 production line. I assembled the first 10 production units or so, IIRC 4 went to the BBC and the rest to rich arabs.
I recall lifting a pair into the upstairs demonstration room - they were a 4-man lift - I stayed on after work when the factory was quiet, and listened to them until my ears fell off - I briefly compared whatever the current best CD player was at that time (Meridian's first 14 bit player, Philips based??) with a Sondek, but the speakers volume and hence dynamic range made the vinyl sound compressed vs CD, so I worked my way through the entire CD collection.
Laurie Fincham was Kef's R&D director at the time, now at THX apparently, and has some youtube content out which I must look at!, and Rick Ciccone plus a Canadian guy whose name I don't recall were the project team, with me on assembly duties. Kef did the cabinets and drivers, any electronics issues the amps were pretty much standard Quad 405s IIRC. We matched the drive units carefully (as was common practice at KEF), there was a 10mx10mx10m measuring room where the drivers went through individually, then a mini computer did an FFT analysis on the output produced by a 'click' input (delta function) and the results were sorted into matched pairs for response & sensitivity.
I've seen a couple of inaccuracies in various sources that are worth mentioning - the bass drivers were individually driven by their own 405, not bridged as some sources say. The midranges likewise were driven directly, and just the tweeter was bridged - so 8x 405s total in spite of what the science museum website says! (but you'll know that..) The tweeter was ferro fluid cooled, not the midranges - and we had some problems in testing that when the tweeters were driven too hard, the ferrofluid pissed out and overcooked the voice coils. I think the tweeter 405s were down-specced power-wise as a result.
I assembled the tweeter/ midranges in their little wooden box, which was damped inside with polyol (sp?), then they got tested again before the box got bolted into the internal frame that carried the electronics, with the bass boxes bolted on either side.
I got the gig at Kef having worked holidays previously at Boothroyd Stuart/ Meridian - Bob Stuart put me in touch with Laurie. Meridian used pretty much wall to wall KEF drivers, and it wouldn't surprise me in the least if Bob had some input on the KM1 design - not least the crossovers. Bear in mind this was KEFs first active speaker, and Meridian had been doing the M2 & M3s for a while (I still have a pair of both. M3s still in use!)
I'll be watching your thread with interest - all the very best on getting them going again! I'm not sure I can be of any use in the rebuild - it was so long ago, and I was both junior and part-time - but feel free to pm me if I can help. I'll try to find the couple of photos I have of a brand new one on the shop floor at the Tovil factory....
regards and best of luck!
Martin
Paul Marchant
pfm Member
Good to hear from someone else who's been involved with the KM1s. Information, and people have been hard to find.
I have a question for you, if you were the 'putting the midrange enclosures together' chap. I'm having difficulty getting the midrange drivers centrally located in the slightly oversized baffle recesses. Was there a trick you used to get them accurately located?
Cheers,
Paul
I have a question for you, if you were the 'putting the midrange enclosures together' chap. I'm having difficulty getting the midrange drivers centrally located in the slightly oversized baffle recesses. Was there a trick you used to get them accurately located?
Cheers,
Paul
Hi Paul, now you're asking - really getting me to cast my mind back! Having a proper look through the thread and seeing all the pics brings back happy memories - although the ported version wasn't a thing when I was there.
Ref centering the midrange units, I don't fully recall, although I vaguely remember a plastic up-stand insert - sort of a skirt thing - that went around the driver hole in the baffle, to stop the polyol mastic damping sludge from messing up the driver mounting. The polyol went in as a custard-thick gloop that started to set in 10 secs or so, it was pretty runny so needed keeping in place. Is the back of the baffle covered in it? If the insert were left in place while the driver was installed, then discarded, that would account for a mm or so?
Also I see you've made contact with one of the KEF team - do pass on my regards if you're in touch - I was reading electronics (comms engineering) at Canterbury and worked at Tovil in the easter & summer holidays in 1984. I have a feeling I know who your contact is - I don't recall his name but can picture him - he was one of those rare people who retains knowledge without any seeming effort!
Ref centering the midrange units, I don't fully recall, although I vaguely remember a plastic up-stand insert - sort of a skirt thing - that went around the driver hole in the baffle, to stop the polyol mastic damping sludge from messing up the driver mounting. The polyol went in as a custard-thick gloop that started to set in 10 secs or so, it was pretty runny so needed keeping in place. Is the back of the baffle covered in it? If the insert were left in place while the driver was installed, then discarded, that would account for a mm or so?
Also I see you've made contact with one of the KEF team - do pass on my regards if you're in touch - I was reading electronics (comms engineering) at Canterbury and worked at Tovil in the easter & summer holidays in 1984. I have a feeling I know who your contact is - I don't recall his name but can picture him - he was one of those rare people who retains knowledge without any seeming effort!
If you raise the two ends slightly and make them say 3-5mm higher, then the weights in the middle will better be able to push the centre down. There will be a small tendency for the grill to spring back so you need to go slightly over centre to take this into account . Follow this link for the general idea https://www.baileymetalprocessing.com/techmatters/blog-category-1/2018/12/17/springback
links here:
in the dem room
drive.google.com
on the shop floor with yours truly at right, Dave(?) the Canadian on the left
drive.google.com
on the hydraulic lift in the middle of the test room. That was nerve wracking as it went up I can tell you - balance problem.....!
drive.google.com
in the dem room
KM1-1.jpg
drive.google.com
on the shop floor with yours truly at right, Dave(?) the Canadian on the left
KM1-2.jpg
drive.google.com
on the hydraulic lift in the middle of the test room. That was nerve wracking as it went up I can tell you - balance problem.....!
KM1-3.jpg
drive.google.com
Paul Marchant
pfm Member
KM1-3.jpg
Thanks for the pictures - I've not seen those ones before anywhere. I'll add them to my KM1 folder, if that's OK with you.
I've made it public via this link:
KEF KM1 – Google Drive
drive.google.com
in case it helps anyone else trying to get a pair working. It's got all of the information I've found so far and all of the pictures.
If you'd prefer not to have those pictures in it, let me know and I'll 'hide' them.
I think the 'Dave' that you refer to would have been Dave Smith. He worked with Ric on the development of the KM1 and then subsequently went on to JBL and Snell amongst others. He was quite active on a couple of the loudspeaker forum pages in the US, where he lived. Sadly, I understand that his health problems came to a head in January of this year and he's no longer with us.
Hi Paul, very happy for the photos to be public, the reason you haven't seen them before is I took them and they've been sat in an old box for 40 years!
Dave Smith does ring a bell, really sad to hear he's gone, he was a nice guy.
There was a slightly backroom boffin called Phil iirc, Ric was the lead but Phil did a load of the theoretical/ design work I think.
I've been racking my brains about the b110 centering, and I really don't recall any heatsink bar- I wonder if that was added later? I know we struggled a bit with tweeter heat-load, but I don't recall the 110s having ferrofluid either- it was seen as a tweeter problem not a midrange problem.
The ones I worked on were the very first apart from a hand-made mockup, so the design would have evolved anyway.
Have you got all the drivers sorted now? I think you've discovered that the 300s we're low-impedance and specific to the KM1? The 110s were bog standard I'm pretty sure, and we selected them as the closest sensitivity matches from the big factory batches.
110s we're also in Meridian M2& M3s, so there should be spares around if you need them?
Dave Smith does ring a bell, really sad to hear he's gone, he was a nice guy.
There was a slightly backroom boffin called Phil iirc, Ric was the lead but Phil did a load of the theoretical/ design work I think.
I've been racking my brains about the b110 centering, and I really don't recall any heatsink bar- I wonder if that was added later? I know we struggled a bit with tweeter heat-load, but I don't recall the 110s having ferrofluid either- it was seen as a tweeter problem not a midrange problem.
The ones I worked on were the very first apart from a hand-made mockup, so the design would have evolved anyway.
Have you got all the drivers sorted now? I think you've discovered that the 300s we're low-impedance and specific to the KM1? The 110s were bog standard I'm pretty sure, and we selected them as the closest sensitivity matches from the big factory batches.
110s we're also in Meridian M2& M3s, so there should be spares around if you need them?
Paul Marchant
pfm Member
The tweeters have been inspected by one of your former colleagues (who has asked to remain anonymous, but let's just say that he's the one person on the planet who has absolute knowledge of their design and internal parts) and been pronounced fully working. He's advised I don't attempt disassembly for ferrofluid renewal and that I leave them as-is.
The mids have all been disassembled. They are ferrofluid cooled units, and the ferrofluid had gone sticky / crispy with chunks of 'ferrosolid' adhered to the voice coil formers and causing mechanical interference on one unit. They were the most stressful repair I've ever done on anything. There are many pictures on my Google Drive link. They, like all the other drives, are unique to the KM1. They're polypropylene cones rather than Bextrene, five ohm voice coils, liquid cooled and with the big metal bars going to a heatsink on the back of the enclosure.
The bass drivers are the only outstanding thing. Gravity has done its wicked work, and three of them had sagged to the extent the voice coil former was rubbing on the magnet. I've flipped all of them through 180' by swapping upper and lower units. It's a waiting game for gravity to sag them back into alignment. In hindsight, I should have done this in August when I took delivery of them, but I dealt with the other problems first and only did the 180 degree flip in January. It's been a couple of weeks since I visited the lock-up to see, but at last inspection one had completely fixed itself, one had only the very slightest rub and the last was a lot better than originally but still had significant contact. My hope is that I'll get a bit of time next week to visit them and perhaps all will be well. Again, they're unique with five ohm voice coils, so obtaining replacements is realistically impossible.
Sounds like you just need a bit of luck with the bass drivers then, as you say they were bespoke so repair would be the only option, if it is an option...
I suspect there were spec changes through the short life-cycle - I pretty sure the 110s for the ones I built just came out of a production batch, we just selected the best matched set and sent the rest back to the factory.
Basically you're trying to rebuild a 40-year old speaker that was built out of model-specific parts! Sounds impossible without tapping into your KEF resource, but I say well done you for taking it on and making a go of the whole thing, top work!
Best of luck with gravity then ....
Regards
M
I suspect there were spec changes through the short life-cycle - I pretty sure the 110s for the ones I built just came out of a production batch, we just selected the best matched set and sent the rest back to the factory.
Basically you're trying to rebuild a 40-year old speaker that was built out of model-specific parts! Sounds impossible without tapping into your KEF resource, but I say well done you for taking it on and making a go of the whole thing, top work!
Best of luck with gravity then ....
Regards
M
