Tayda’s jacks are 15.2mm wide, you could have fitted all of them in 5cm, what a waste of space doing it in 10cm 
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You gotta work with what you have 
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There are really two things to consider: how large a gate the modules output and how large or small a gate they will accept as a gate input.
I’d say 5 V is a good gate level to generate. Most other synths will accept that as a gate and it won’t be too large for most synths. Maybe say output gates should be in the range 4.0–5.5 V?
As for gate inputs, there’s no reason not to accept gates down to a threshold of a volt or two.
Ideally gate inputs should allow and be protected against at least 15 V — I think Ken Stone’s designs, for instance, can put out gates close to that, see CGS gate sequencer - Synth DIY Wiki .
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As the “spec” is currently is written, “minimum 4V” means that if you want to be sure that all the modules’ gate inputs will accept your gate output, it should be at least 4V.
The “spec” was written as an attempt to capture the usage in the then current LMNC’s modules.
Guesses were made when not enough data was available.
Several modules have been added since, so we now have more data points.
If someone wants to test how low of a gate the existing modules all respond to, I’m all for it.
Part of the reasoning behind a 4V minimum, is to allow simple designs based on 5V CMOS circuits, some of which require a minimum of 3.5V to detect a “high” input.
Add a minimalistic protection circuit made up of a series resistor and a reverse voltage protection diode on the input, and you’re already close to, or above, a 4V requirement, if any amount of current flows through the diode, even if the diode is schottky or germanium.
Sam does seem to prefer a transistor based input protection circuit though, so this constraint may not be necessary, but a 4V output is not that hard to achieve.
As for the allowed minimum and maximum input voltages, I would suggest ±12V so that no input is damaged by plugging it into the output of any other Kosmo module. (I don’t think we need to protect against voltages produced by non-Kosmo modules.)
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Right, but you make a valid argument that 5 V CMOS circuits would not, without input conditioning, be able to deal with sub-4 V gates which some non Kosmo equipment might supply. (Not that I know of an example off the top of my head.) I guess if it were my design I’d add input buffering to bring low gates up to the 5 V level, but whether such input conditioning should be considered a specification requirement is open to question.
Why not? Many of us use non-Kosmo modules and interface them with Kosmo. True, that’s mainly Eurorack, which should also be covered by ±12 V, but I don’t see why not to protect against ±15 V just to benefit the occasional MU/MOTM/etc. user and to be on the safe side.
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Noob question but I would rather use 3.5mm jacks than the 1/4" (I’m a heathen, I know lol) Would it literally be a drop in change when making? i.e. instead of 1/4" just use these? and if so is there anything I need to know about it beforehand? They seem 1:1 other than size and layout. Thanks 
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thats what I do , just have to use a washer on the face panels with holes made for 1/4" jack sockets . and it does require some extra work on the modules that the face plate is held on by the pcb mounted jacks , but its doable .
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Perfect thanks! (Looks really nice btw!) Do you by chance have a link to the washers you buy or at least the inner diameter dimensions? Thanks!
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these are probably over kill but being stainless steel they are strong for how thin they are .
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If you are going panel mounted with DIY panels and panel mounted jacks. I Suggest these PJ-301BM 3.5MM MONO PHONE JACK They have a little bit more metal and less of a chance of breaking if they are panel mounted and not pcb mounted. Downside is most eurorack kits use the PJ-3001F 3.5MM MONO PHONE JACK.
Also suggest getting Thonk Hex heads for the jacks they are better for tighting and work better then the nut that comes with the jacks. Hex heads
Also using the washers is a good idea if you plan on using premade panels like LMNC for 1/4 jacks. I made a delay pedal and Did the same thing replacing the 1/4 jacks with a 3.5mm with a large washer. Turned out pretty good.
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yeah defiantly get the thonk hex nuts I bought a bag of 500 and they are almost gone . those jacks with the metal case look nice . I have been buying the cheap plastic bodied ones because I have needed so many , they haven’t been to bad but they do break apart sometimes .
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An annoying thing missing from the KOSMO spec that has kind of burned me a little bit is the height of the mounting rails. I made mine a little too large and need to shave them down a little bit to fit in the insides of some the taller modules (PCBs+Jacks). I’m guessing it should be about 6mm?
It doesn’t seems to be in this thread, but it says 10mm here :
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It’s implied by
so 25 mm is reserved for rails, 12.5 mm per rail maximum. Screw holes are 3 mm from the top and bottom edges so ~ 6mm minimum is also implied.
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Excellent point.
There are those of us who like to use aluminum rails, and some rails have lips:
That’s a Z rail, and the drawing is maddeningly missing some of the most important dimensions. But it does appear to be to scale in which case the nut slot is 6.5 mm wide and the aperture in front of it is 4 mm wide. M3 slide nuts are 5.5 mm wide. So the panel holes must be 194 ± 1 mm apart.
The distance from the center of the slot to the inside of the lip is 3.8 mm. With two rails at a slot to slot distance of 194 mm, the lip to lip distance is 201.6 mm. Any panel larger than that won’t fit.
Vector rails have no lip
They use M2.5 slide nuts. I’m not sure what their width is. But the slot aperture is 0.118" = 3.0 mm, so there’s only ±0.25 mm play there, however there’s also ±0.25 mm play in the 3 mm panel mounting hole, so if I’m thinking straight that again leads to 194 ± 1 mm hole distance. With no lip, the rails do not constrain the panel size as long as the hole distance is right.
If I’m thinking straight.
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In terms of Case Depth ill let you all know how I get on with 15cm sides with a 2.5cm indent.
That way, you guys with 20cm depth have 5cm more freedom =D
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I continue to find myself bemused by the Kosmo community’s proclivity for deeply inset modules. The old classic Moogs — both the studio models and the Tolex-covered roadworthy ones — weren’t built that way; neither are most Eurorack systems. In fact on a brief search I could not find any instances of non Kosmo synths with front panels set back more than about a centimeter; most seem to be a few mm, or even flush.
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Meanwhile, my ugly case design mounts over them 
.
Might eventually care enough to build another more proper case, but probably not!
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I blame Sam =) Also, it means you can stick LEDs and clip things to the sides
guess I felt the knobs would be more protected if they were set back a bit . yes in hindsight it does make getting to jacks / knobs on the out side edges a little more difficult . I am thinking once I get everything up and running I will build some nicer furniture like cases .
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