deskthority

Devlin Goody Bag no. 2 arrived today from Nick Hoskings. Nick originally told me I'd be getting some Mitsumi KLT2 switches, but having checked the part number, he's determined that they're KLT-11, and KLT2 might be the product range. They're moving premises, and Nick saved these from being thrown out, but all the paperwork is already gone. Google has no record of either code, so we may never know.

I wasn't sure what I would be getting; it turned out to the adorable little mini switches! 29 of them:
Specifically, Cherry MX mount and tactile. And by "tactile" I mean it — it's quite possibly the most tactile switch I've ever encountered. Measurements using five different coin arrangements and five different switches gives me the following weights:

{ 60 g, 68.45 g, 76 g, 70.4 g, 67.05 g }

It's roughly the same weight as Cherry MX Clear, but the force curve is perfectly smooth and clean, without all the jittering of MX Clear, and the tactile point is a smooth, tight curve instead of a hard point. It's hard to determine which of KLT-11 and SMK second generation is better; the KLT-11 feels that little bit smoother. Granted, the switch has a rough feel — I doubt that it's a patch on some of the ultra-smooth vintage switches HaaTa has got, but it blows Cherry MX clean out of the water and probably right off the planet. The "lateral buckling spring" approach also makes it a lot smoother than Matias quiet click, which has a lot of nasty bumps in the force curve all the way down.

The only gotcha would be if it suffered from off-angle binding; I can't test this as I don't have a keyboard of them. I've never heard of this, but it's such a rare switch, it's hard to get a handle on its reputation.

Apparently Devlin used KLT2 switches extensively until the late 90s, at which point they were converting from KLT2 to Cherry MX; I imagine Mitsumi jacked in the product range before the upturn in the mechanical keyboard market around ten years later. It's quite tragic really, as these are beautifully engineered little switches — extremely intricately made, even more so than Omron B3G-S. It's impossible to dismantle the switch as numerous plastic sections are permanently driven together in the factory, and you'd slice off your thumb with a knife trying to prise them apart again.

(Looking at the [wiki]Mitsumi miniature mechanical[/wiki] page, there seem to be numerous errors, including two references that report the wrong colour with respect to the photos on the referenced page. The total number of combinations of these doesn't seem to be that high; I'm going to replace the colour table with a proper variants table.

Also, someone once said they'd seen/owned clicky ones, but I'm not able to substantiate this claim, nor do know where you'd get a clicker inside such a diminutive product.)

It's hard to tell from photos exactly what size they are. They're the same width as a Cherry MX switch, but much shallower front-to-back, and not quite as tall:
Mine have the old Mitsumi logo on the base and the new one on the side:
The front panel can be prised up like a car bonnet to reveal the contacts:
If you bend it back down it seems to snap back into place and stay fully closed. I've tested a switch after doing this with a meter and it still registers correctly. The "bonnet" holds the contact frame in place; you can prise the contact frame downwards:
The contact frame is formed from the same piece of plastic, with a "skin" keeping it attached to the rest of the base. It's formed from two layers with the contacts sandwiched inside.
A small piece of plastic is inserted through the movable contact, and the slider presses on this to hold the contact open. When the slider is depressed, this plastic part drops back into a recess in the front of the slider, allowing the contact leaf to spring into its closed position. This makes it a "negative" contact switch like Cherry MX, so the keystroke force never reaches the delicate switch leaf; all forces on the leaf are set in the factory.

The spring is slung laterally under the slider:
(That's the largest photo I can take, as my camera doesn't have sufficient control or intelligence with the flash during super macro mode, and if I get any closer the image gets blown out — so that's just a crop of the centre. It depends on the camera's mood, of course.)

It's very hard to tell from the photos, but the peg in the base that would normally hold the spring, has a wide groove across the top to hold the spring laterally instead. As the slider is depressed, this spring is pulled down over this centre peg until it buckles. Just as with normal buckling spring, the tactile force is drawn off a single spring — there are no hooks or ramps for the tactility, which gives it its ultra-smooth force curve.

Comparison with Alps SKCL Yellow:
Those brainy Japanese guys know how to get these things apart, but I can't figure it out. The first attempt wasn't even an attempt — in the end I just tore it apart to see if I could figure out what was holding down the lid:
With the switch ripped apart you can see the specially-shaped guide recess in the centre peg:
I could see that little ramps on the inside the plate retention clips were holding down the metal lid. I took another switch and tore both retention clips right off the switch, and the lid came off easily:
What's hard to see, is that there are two extremely tiny ramps, one per side. The lid sides only have to be lifted a fraction of a millimetre to pull clear, but they're locked down by the ramps on the inside of the retention clips. I guess if you had lots of very thin tweezers you could somehow lift the plastic ramps and then force up the lid sides from behind, on both sides at once. I'm not too fussed as there are plenty of photos of these switches open, just very few showing how they actually work.

Finally, an inside view with the contact frame still present, showing the plastic doobrey from the inside.

THks for your pictures.

I have some used Mitusmi switchs just like this ,the color is green and yellow.

The spring rub against the switch is not so comfortable.....

Nice pictures and interesting switch!

Awesome! I have a mitsumi keypad I used for binds in Garrys mod. I never realized how strange they were inside. They are very tactile and have a comfortable force curve like you say.

I'm going to contact Mitsumi and see what they can tell me about the part number. I found a business card in the envelope from Nick, on which he wrote "KLT II", which suggests that "KLT-11" means "KLT-II" which means "KLT2". Mitsumi's current switches all have three-letter series codes, so "KLT" would be the whole series. We will have to see.

cherry-jade is right in that it's got a "frictiony" feel, although it's not scratchy like Cherry ML.

The "slung buckling spring" approach gives you an unrivalled force curve at the expense of having a rougher feel than other switches. It's a difficult trade-off. Personally I'd drop the wire gauge a tad and reduce the force by 10 g or so, as the pretravel is a little on the low side. It's a firm touch switch, and something that MX Brown haters would do really well trying.

Sounds a good one. Probably the first MX compatible smooth tactile switch. Well, smooth bump anyway. The recent Topre migration to MX mount (surely the NovaTouch isn't the end of it…) adds a second.

Do we know any keyboards built with these?

Devlin used them extensively but I don't know what the products were. Chicony in particular used the ones depicted above.

The known keyboards are given here:

[wiki]Mitsumi miniature mechanical[/wiki]

There's a video on YouTube appearing to depict a Nan Tan board with them in, but the model number is not known. I forget whether that was being looked into or not … that was months ago.

I have had two Chicony boards with these switches, plus some numpads with other color stems. I have passed all of these boards on to Haata, who has them in his extensive picture repository. Perhaps you can compare the internal workings of the different variations of the switch with the ones he took.

HaaTa has confirmed that clicky switches exist, but since they're extremely hard to open safely, we may never know what's inside unless he's prepared to risk sacrificing a switch. (MouseFan appears to have done it, looking at his pictures, but then he's clever. HaaTa could probably do it too.)

The wiki page does now have an illustrated variants table of every variant HaaTa and I know of. There's potentially one more know variant, Mitsumi mount and cream, looking at Ripster's photos.

i would love to try these out on a keypad or something. burroughs-lite?

Today the Chicony KB-5191 with Mitsumi KLT-11 switches came and I got the chance to try these switches while mounted on a PCB. The bind really bad on off-center key presses, I don't know if that is because they are PCB-mounted and not on a plate. Otherwise they feel pretty much the same as a loose switch. They feel really nice as a single switch, so I will try to plate-mount and test them again, but so far I'm a little bit disappointed of them.

At least I have some switches I can disassemble and photograph now.

Not too many now, they're a nightmare to get back together!

How consistent are they across the keyboard? Any unwanted clicking? Weird to hear about off axis binding. I put wide caps on my loose ones and tried that. Mitsumis felt better than Matias in that respect, and just as good as MX.

I'd say they're quite consistent across the board, although some of them squeak a little bit on the upstroke. No clicking so far. I have to test them a little bit more to come to a final conclusion.

Edit: I'm typing on it right now and especially the left control key is nearly unpressable because of all the binding. At least you can't press Caps Lock accidentally on this keyboard. Some switches seem to bind more on off-center keypresses than others, but mostly they feel bad. The stabilized keys feel quite nice, they have something like PCB-mounted Costar stabs. These switches make my hands hurt, because of the binding, so I'll stop this test now.
Also, after just a few weeks of using a 60% I'm not used to a full-size keyboard anymore, it feels way too big.

Binding is always a tough one. I have a white Alps keyboard in really nice condition that's nearly impossible to use because of the binding, even on single-unit keys — I have no idea what's gone so badly wrong there; my Nan Tan white Alps keyboard is fine. My SMK keyboard feels a bit worse for wear, too.

I don't recall ever hearing about Cherry MX switches suffering these kinds of defects with use, though. They can still degrade, but never to the extent Alps does. Mitsumi, I couldn't say, though binding isn't a complaint I've heard about them yet (nor of SMK).

I have a few white alps boards that also bind and\or are scratchy beyond use. I've always assumed it's just dirt or corrosion from being stored in a damp location or something.

I've tested the loose switches with a 2u keycap, but then the binding isn't really noticeable. However if I press the switch a bit askew with a high keycap (e.g. SA) mounted then the binding is pretty obvious even on a loose switch.

I wouldn't be surprised honestly — there's got to be some sort of trade-off for having all that travel in such a tiny switch.