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Eurorack Case Design Plywood Thickness and Power
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Eurorack Case Design Plywood Thickness and Power
Hi All,

I'm about to take the plunge, and have a case laser-cut.

I'm planning to adapt Nonlinear Circuits' 21U Studio Case to be 126HP wide, and I have a couple of questions:

1. The specified 7mm ply doesn't seem to be available in the UK. 6 and 9mm are available, and I initially adapted the original 84U design for 6mm. However, I'm wondering if 6mm will be thick enough, with the case expanded to 126HP. What do you think?

2. I have no real idea what I'm going to need in terms of power. I was thinking of going the Meanwell route, but will I be able to get away with a single PSU, in a case of that size, or will I need 2 or more PSUs?

Sorry if these are stupid questions. I've been putting off having a case made for a while, now, because it all seems very complicated. However, my stack of modules that don't fit into my existing 5-row, 84HP rack sleeve is getting bigger all the time, so I either have to sell a load of modules (probably the more sensible option, in fact), or get/make something bigger for them.

Do you have a modular-grid plan for the full system?

You can't really plan a power solution for a rig that size without knowing something of the modules you plan on using: you can view rack plans of 9u systems that use 700mA on the +12v rail, others that need 1600mA in the same space. It all comes down to module selection.

If you scale that up to the size of the case your building, then the potential difference in need is huge.

6mm is not very sturdy, I think. I used either 9 or 12 for my case with lasercut sides (all my other cases are 18mm oak), and even that feels pretty light. If you don't put big washer underneath the screws you'll just bury them into the wood (at least with the lightweight plywood).
If there's some kind of box joint contour on the plans (not familiar with those drawings) you'll have to adjust the height of the castellations to suit the thickness of the plywood.
There are pretty hefty dual output meanwell units, but you can just as easily go for two single units (or split the case up into two sections each with it's own meanwell dual output unit).
I now have 2x5A (two single units each 12v 5A) in my case which is 4 rows of 230TE wide, roughly the same give or take half a 19" rack width smile
However, it is not fully filled up yet, and I do have about 120HP/TE on a different PSU (2x15V), that same PSU also supplies the 5volt bus (7A). YMMV
9mm sheets. 6mm will yield weak finger joints and may not resist warping after the case is assembled. In a project of this size, clamping pressure during assembly may distort 6mm stock.

However, if you plan to use NLCs source files to drive your laser cutter, you must use the specified thickness of material. Otherwise, the pieces may not fit together, and if they do, the joints will not be flush.

How much power you put in is determined by the class of modules you want to use. I you want to use all analog circuits (ex: most Erica Synths), you might get by with something capable of 2-3A on the +12V rail. If you are mixing in modules with MCUs or CPUs (ex: most Mutables), you will need to double the power. The modules in my collection are a 50/50 mix of digital and analog modules.

In a case this large, you may install two smaller PSUs, each with its own power bus, but sharing a common earth distribution.

I am currently building a monster 21U x 252hp case, and using 3 x 3A PSUs. I'm using some used PowerOne HCC-15-3.0 linear supplies that I scored cheap on ebay and rebuilt with all new caps and drivers. This is the old school way. New switching type supplies such as those from Meanwell are less bulky and more efficient (produce less waste heat). They are easier to mount as well.

Another factor that comes up when using digital modules is that the imbalance between load on +12V and -12V rails goes way up. This would then suggest the approach mentioned by Jarno above, where you put in a large +12V supply that carries most of the overall load, and a smaller -12V supply.
I have a DIY 10mm PLY case and I find it strong enough. I think that 9mm PLY would be adequate as well.
6mm seems very thin. If it's regular plywood, I would be using 12mm minimum. At 6-9mm I would suggest that it be baltic birch plywood which will maintain its shape much better at those thicknesses.
I am not sure shops are cutting that nice baltic birch ply, you are right, that is very stable indeed. Most of the ply cut on lasercutters is the lightweight stuff, as that lends itself to lasercutting better.
Guys, thank you very much for all your replies, and apologies for taking so long to get back to you. I thought I had set a notification on the thread, but it looks like that didn’t work, for some reason.

I will digest all your excellent advice.

I’ve decided to go for 9mm ply, as a local laser-cutting business happens to have some in stock in large enough sheets.

I’ve adjusted the height of the ‘fingers’ to account for the thinker material, so the joints should fit together nicely, hopefully.

Next move is to add the cutout for the power socket. I was thinking of putting it on one side, rather than at the back. It’s a bit messier, but I may want to mount the case against a wall later, so a powe silver on the back would get in the way.

I’m also wondering if I’ll need to add slots for ventilation. I haven’t seen many cases that have these, which I find surprising. Anyone any thoughts on this.

I had my case laser cut at Pololu Robotics and Electronics in Vegas. they have a BIG ass bed and will cut 1/2" ply birch
Joe. wrote:
Do you have a modular-grid plan for the full system?

I don't. I should try that, but I'll have to split it into several racks, as there is a limit to the size of a rack, unless you pay a subscription.

Having said that, I'm not sure exactly what modules I will be using. A good proportion are MCU-based, however (including all the MI modules except Elements), so probably best to err on the side of over-speccing the power, I guess.

It turns out the fab were quoting me for poplar ply. I've asked them to quote for 9mm birch ply, instead, which should be stronger.

I've made a little spreadsheet with all my current modules.

This is what I have.

+12V: 3983mA
-12V: 1140mA
+5V: 305mA
HP: 731

Power doesn't include a load of Falafular drum voices that I don't have any data for, but I guess they're minimal (and all analogue).

Looking at the specs of the Meanwell RT-65B I had in mind, I'd definitely need 2, but unfortunately, the -12V channel is only able to provide 500mA, so even 2 of them wouldn't (quite) be enough.

On the plus side, I will have over 100HP left, with all my current modules installed, which is great (though Bad for my bank-balance, of course).

Anyone any experience of this PSU?

2 or these would provide enough power for me, I think.

I’m building a couple of the metatronic supplies. Easy build. Will see how it fares in use.
Cool @DisappearHere let us know how it goes.


How'd it go with that power-supply?

I´d do at least 12mm plywood for that size and I´d do 2A for every 300HP minimum. So in your case 3x Doepfer PSU3´s or whatever the Meanwell equivalent is.
6mm is def too thin in my opinion for anything more than a small testing rack or something. Ive made all my racks out of 12mm and I havent had any structural issues at all. Although using 12mm will def be a bit heavy
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