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Kef KM1 in need of repair.

As a lover of all things 1980’s Kef Reference, I have found this thread and the restoration utterly fascinating.

I have read the linked thread with the chap from Kef. There a few old Kef chaps knocking around on FB and the forums that are remarkably helpful.

You’ll have to find a pair of Maidstone 109s to keep these company.

And looks like you have a ‘path to fix’ for everything, which must be a relief.
 
Blimey that ferrofluid is expensive!

I presume it’s a specific type? As you can get tubes for a fiver?!

Edit - found Ferrotec’s website and had a browse. Wow so many variants I’m amazed. Used by nasa to transport fuel in zero gravity too … how cool.
 
Rug Doc said:
Blimey that ferrofluid is expensive!

I presume it’s a specific type? As you can get tubes for a fiver?!

Edit - found Ferrotec’s website and had a browse. Wow so many variants I’m amazed. Used by nasa to transport fuel in zero gravity too … how cool.
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There are many different types of ferrofluid that Ferrotec manufacture. I think (hope) the one I've bought is the current version of the stuff KEF used to buy from them.

It's not too bad, per millilitre, but annoyingly I need - at most - 3ml. I had to buy 76ml of it. It would appear that despite Ferrotec's ability to precision manufacture lots of different types, they're unable to purchase smaller plastic bottles to sell it in. Sigh...
 
You could make your money once you’ve done yours advertising it here in the classifieds and sending it out..?
 
Rug Doc said:
You could make your money once you’ve done yours advertising it here in the classifieds and sending it out..?
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But, maybe being able to charge five quid a time for it... I've got to find containers, packaging, drive to the post office... I don't think there's any real profit to be made, or even the chance of covering my cost unless I'm doing it a hundred times.

If someone lived nearby and wanted to turn up with a bottle and grab some for free, I'd be happy to give it away. Might be useful to someone...
 
Things have taken a downwards turn. I might be in trouble here.

So, I put some fairly high level (a few watts) test tone into the mids to check for coil rub... and I've discovered something that has brought dread to my heart.

It seems that the voice coil is partly detached from the cone on one of them.

The edge of the cone has crept over the top edge of the voice coil former. I gave it a gentle touch with a fingernail to establish whether I was looking at half millimetre of the cone folded over the top of the coil former, and it's become clear that the adhesive bond between the two has failed.

If I manipulate the cone gently, I can see relative movement between the two.

There's no obvious damage to either part... and I presume that which was once glued can be glued again.

Any words of wisdom on this? I think it's beyond what I can personally do, and it's going to have to go to Wembley Loudspeakers for them to fix.

I'll publically state, at this moment, that I'm willing to sell a kidney to anyone who'll take it in exchange for selling me another one of these midrange drivers.

I'm kicking myself for missing out on the pair of mids that were up on Ebay.com until recently.
 
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I certainly hope they can. It's exactly the sort of potential issue that put most of us off in the first place and in fairness the vendor was totally "up front" about it.

I have a dead SBL bass driver with similar issue and nobody reputable will touch it!
 
What terrible luck, but unsurprising given their visual condition.

Whilst I am sure Wembley Speaker can get this driver working again, whether they can do so in a manner that ensures it visually and audibly matches the others and can cope with the sort of SPLs these speakers are designed to deliver is another matter entirely.
 
Well, things are progressing in a positive way. I've been conversing with one of the original designers of the KM1 on the hifiloudspeakers forum, and he's volunteered to inspect it and let me know what he thinks my chances are.

Him being one of probably only three or four people on the planet who definitively knows about these loudspeakers in detail, I'm very much interested in his opinions. I hope to meet up with next weekend.

I'll update you all in due course...
 
Paul Marchant said:
Well, things are progressing in a positive way. I've been conversing with one of the original designers of the KM1 on the hifiloudspeakers forum, and he's volunteered to inspect it and let me know what he thinks my chances are.

Him being one of probably only three or four people on the planet who definitively knows about these loudspeakers in detail, I'm very much interested in his opinions. I hope to meet up with next weekend.

I'll update you all in due course...
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Excellent, the journey is becoming as exciting as the speakers themselves.
 
Things are looking up again. The former KEF designer has managed to fix the midrange for me, for which I'm eternally grateful. :):):):):):):):):)

Having watched the process, there's no way I'd have been able to do it myself.

Whilst, on the face of it, I understand the basic concepts behind the repair, I also understand the basic concepts behind manned space-flight. That doesn't mean I could do either myself.

Next bit of fun is ferrofluid and then fitting replacement dust-caps to the drivers that need them.

After that, I've got to fix one of the amplifier racks. Fortunately that sort of repair work is very close to what I do for a living, so it's a minor inconvenience and a lot of moving big heavy things around and finding a big enough clear bench at work so I can splay it out to get to its innards.

Then, I feel a ceremonial test-assembly and power up is in order. And making a l-o-t of noise with them.

I'd get away with doing it at work one evening. Fortunately my (awesome) boss is both a broadcast engineer and a former record producer and has been most encouraging about the whole thing so far.

I'm not sure of the timescale for this as I'm busy at the moment. I've worked the last 21 consecutive days and have stuff I need to get done at home this weekend, so that's probably it for now.
 
How kind of him. I’m tempted to buy those Wilson’s on eBay Tony posted up on the eBay forum and deliver those to your lockup for restoration too… :D
 
OK, so I went in to work to reinstate the midrange driver that got fixed this morning, with the intention of doing that and then going straight home.

Traffic to home (a fifty mile drive) looked a bit dismal, so I've stayed (also, work has aircon), and had a look at the amplifier packs.

https://i.imgur.com/2B0kBRl.jpg

One appears fully functional. I've only got the mid / tweeter cabinets here (the bass bins are at my lockup), but I've run the amps up and put good level through the mids and tweeters. I've scoped the bass outputs, and they look fine on one amp pack.

The other has about 10v DC offset on one bass output. Time now is 16:37. Let's see how long this takes to diagnose... update shortly.
 
Paul Marchant said:
Time now is 16:37. Let's see how long this takes to diagnose... update shortly.
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An embarassingly long time, it seems - 90 minutes to fault-find what is essentially a board out of a Quad 405. In my defence, there was a lot of disassembly of casing and mounting hardware to get to the board.

IC1, which is a boring little TL071CP op-amp is the root of all evil it seems.

It's gone leaky internally, putting about half its supply voltage through to its input terminals, and then faithfully amplifying the DC along with the incoming audio signal. I haven't seen one fail like that before. It's a conclusive diagnosis, because in the end I got frustrated and removed all of the components in the feedback path which could be routing volts in from elsewhere. I put it back together and then spotted that the fault voltage increases over the first few seconds the board has power. Cooling the IC with an inverted can of air-duster makes the fault come and go.

Sadly I can't Amazon-Prime one for tomorrow, so I've ordered a few from Rapid Electronics... presumably to arrive at my house on Tuesday.

Annoyingly, I now have to spend half an hour reassembling the thing to put it safely away until the parts come in.

I'm fairly confident that this is the only fault and that as soon as I get a chance to fit the op-amp it'll be 100% ready to go.
 
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