Eurorack Monster Base, the build

If you found this post via a web search by all means do check out my previous post about the design of this build. You know, to give more context to all the hands-on, wing-it-as-you-go build stuff that’s about to follow!

This build is a Doepfer Monster Base inspired large eurorack case with a few bays for 1U 19″ rack modules! I’ll start with.. 

Materials

I had a bunch of leftovers from previous builds (etc.) that needed to go, and so a lot of those ended up in this build. I had stuff like clear acrylic sheets 4000 x 500 x 5 millimeters (kitchen renowation scrap), some 18mm thick pine board (old shelves), a 21mm thick plywood (old kitchen cutting board), 3 meters of wooden floor trim (floor renowation scrap), some bits of 9mm thick plywood and ~1.6 square meters of tolex (both from TTSH).. And some wood trim from the 1970s Hammond transistor organ hack aka MIDI Pedal Board.

As for the electronics & eurorack hardware, my friend Väinö from Moraydular was looking to part with everything I needed for the build. From him I bought two pairs of 1 meter Gie-Tec rails (= 400 TE / HP total), rail mounting & threading screws, a whole bunch of M3 nut strips, 4 large Moraydular bus boards (14 connectors each) and a used Power One HBB15-1.5AG linear PSU (1.7A max. on each voltage rail).

Power One HBB15. Photo by celiar.blogspot.com

Toslink adapters. Photo by Ebay.

Other parts I had to buy were 2 pcs of both Toslink XLR Coupler adapters and 50cm cables, 40 pcs 16-pin IDC male bus board connectors, 100 pcs M3*3 plastic spacers, a IEC power socket, a surface-mount Schuko socket outlet, 8 pcs XLR and 3.5 mm jack connectors and 5 meters of shielded stereo cable.

All of this added up to about 220€, which I think it’s pretty super for a 400 HP eurorack case!

Basic frame

In overall my frame / case design builds around a pair of inner side panels 9mm thick, to which the other horizontal frame parts mount to. Finally these inner side panels get covered by outer side panels to hide screws, tolex seams and panel edges, thus making the overall appearance more clean.

So to boot with I cut the inner side panels to shape and test-fitted the Gie-tec rails:

It’s a start: Rail spacing all good, Eurorack modules fit!

Besides through holes for Gie-Tec rails, the side panels have slots cut for top & front horizontal wood supports (floor trim scrap) and smaller bits of trim fastened on the inside (Hammond leftovers), to which the back & bottom panels mount to. Bottom panel mounting trims have M6 tee nuts on them to make bottom panel the ‘service access door’ for this build. Like this:

Near-final inner side panels. Tolex applied only to visible areas in completed build.

The middle support was most importantly, by design, there to have a solid center mounting point for the 19″ rack rails and all surface panels. I made it using the 21mm thick cutting board scrap; this was great for M6 tee nuts as they could be hammered in place without adding any additional trims to the sides.

Middle support cut about according to my initial design..

..and the more final piece after I had a chance to test fit panel acrylic. I also removed the small tab to the left for final build.

The vertical part of middle frame was angled, by design, to have some support for the eurorack bus boards. But in the end I chose to install them at a 90-degree angle. This gave the top module row more depth to install any skiff unfriendly modules (depth > 60 mm). Bottom row, on the other hand, can fit modules about 70 mm deep.

The top & front horizontal supports weren’t included in my original design, but after doing some tests with the acrylic sheets I decided to add them. When drawing the plans I had no clue how much weight the 5 mm acrylic might be good for, if supported only by the inner side panels & middle support. Material tests proved they weren’t good for much so I adjusted plans on the fly and added the trims.

Top & front horizontal support trims (floor trim scrap)

Why the top horizontal support is needed is, without them the acrylic bends in quite a bit when my TTSH sits on top. By design there’s a ~1 mm gap between the top panel and the topmost Gie-Tec rail for ventilation (as the PSU heats up quite a lot). This gap gets blocked if the acrylic bends in too much.

That’s A Nice Rack!

For me the most important reason to include some 1U 19″ rack device bays to the build, was to be able to install my AD-DA converter (Behringer ADA8000) with the eurorack modules. The whole setup just becomes so much more integrated like this: From the converter I need to run only a single ADAT lightpipe pair to my soundcard (RME FF800) for 8 channels of audio I/O. Way more convenient than analog breakout cables or such! And this was what the Toslink couplers & cables were for: To route the ADA8000 lightpipe ports to the back panel.

The other 1U slot can hold a multi-effects unit, a synth module or whatever I find will come in handy at a time. I currently have in it a modified Vesta Kaza VestaFire DG-3 dual gate unit (afaik a pre Vestax brand) which, in modular synthesizer context, becomes a dual Attack-Release envelope generator + VCA in a single unit. Handy stuff, and I may write a post about it later ;)

Right-side 19″ rack bay rails from the inside..

.. and rack units are a good fit too!

Panel Details

As you may have figured out from the previous photos, I started panel work with the bottom piece. It’s the biggest and the most straightforward to complete, as it only needs six M6 holes drilled for the mounting screws and tolex applied. I also added rubber feet (TTSH leftovers), so that the case won’t slide if it ever needs to sit on a sloped tabletop.

Bottom panel with rubber feet

For mounting all the other panels (top/front/rear) I chose to go with this method where M4 countersunk screws are fastened to threaded holes on the panel. Mounting supports & trims have matching holes for each panel, and the panel is secured in place from the inside with M4 nuts. This allows hiding the screw heads under tolex, making the surface look more clean.

In my case a minor problem with this method was that the 5mm acrylic is barely thick enough to accommodate both the countersunk recess for screw head and threading. After the tolex is applied the screw head can’t be held down using a screwdriver, so it needs to mate tightly enough with the acrylic to withstand whatever torque caused when the M4 nut is tightened.

So to better secure the screws (and work around the weak threading) I glued each of them to the panel, filling the countersunk recess with epoxy before final tightening. I didn’t test the resulting joint for how much torque it can take, but each screw handled moderate tightening well.

Countersunk panel screw install-in-progress, missing epoxy.

Panel screw goes through horizontal support..

..and on the outside, the head is flush with top surface.

Rear panel mounting trims on inner side panels

A this point I was still planning to install a carrying handle to the front panel, and so decided to add the rubber feet on the rear panel too (again, TTSH leftovers). I only had four of these (instead six) so I arranged them like this:

Rear panel mounting overview with rubber feet installed.

What happened with the handle was, the one I had was a bit too wide to fit the final front panel. It did fit while I was test-fitting the acrylic, but come panel cutting time, I decided to add a 45-degree angle on the lower edge of panel so that it would flow smoother towards the 19″ bays (= minimal edge). This angled edge turned out just a bit too wide, so that the lower edge of handle mounting bases would have had no surface contact with the panel. No front panel handle for this build then!

Front panel overview, 19″ bay slots not yet cut. Test-fitting handle.

All in all my tolex work on this build turned out a bit rushed. The build ended up with a few corners where the acrylic isn’t all covered, and I also had to do a 2nd round of spray glue in a couple of places. It may have made some sense to lightly sand the acrylic, so as to have a less shiny and polished surface for the glue to stick to.

Panels tolexed!

One fun little detail about doing tolex over clear acrylic is, any bright light on the reverse side of panel will pass through and make the tolex (kind of) glow in a neat way. I decided to make use of this feature, which brings us to..

Electronics

Here my build plan was ‘PSU first, then whatever’. The PSU came with a good set of pre-drilled M5 mounting holes on its heatsink, and I decided to make use of those by threading some to accommodate M6 screws. Mounting became easier this way as nuts aren’t needed.. And it’s also far more tool friendly way if the PSU ever needs to be removed for repairs!

I mounted the PSU on the middle support with its large aluminium surface facing forward, as it felt like the best solution for air circulation..:

PSU mount closeup

For the main AC hookup I installed a Delta SK-1027 IEC socket. I find this style of socket handy in that it comes with integrated dual 5×20 mm glass fuse bays and DPST mains switch. Just cut a single hole for the part and you’re ready to install!

Delta SK1027. Photo by Mouser.

As there are the two 19″ bays I also needed to have AC sockets inside the case. For that I installed a surface-mount schuko outlet. The PSU and outlet are wired so that mains switch on the IEC socket will cut off AC from both, but only the PSU is fused. 19″ rack equipment come with a fuse of their own, so I didn’t see the need to ‘double up’ there.

It was tricky to get any good shot from the wiring once installed. To sum things up, I used heat-shrink covered Abiko crimp terminals at the IEC socket end, and from there running to a AC screw terminal to distribute L, N and earth wires. Something like this:

AC sockets & wiring

PSU DC output distribution terminal.

For the bus boards I (very much incorrectly) used the same brown-blue-yellow/green wire that I used for mains AC. In general it’s very advisable to differentiate AC & DC supplies from one another by using cables of different color. I was just looking to get rid of these AC wire leftovers I have, nor did I have any other cables with equal thickness of copper in them. Same wire it is then!

Bus board supports are 50*18*1000 mm to which bus boards install directly by small wood screws. Plastic spacers in-between of course. Both supports are sandwiched between the inner side panels, and fastened to middle support with l-brackets.

One fun build detail with the bus board supports was, that instead of paint I decided to wrap them in black duct tape. I can’t tell if it’s some kind of sub-conscious inspiration drawn from all the Inside West Coast Customs binge watching I’ve been doing lately, but it sure was a quick way to end up with a clean dark surface. Remains to be seen how well the tape glue will age..

Bus boards, support trims with black duct tape.

Bus board distribution terminal

Like said I ended up adding some LED lighting too. I had ~4 meters leftover of white LED strip which just happened to fit inside the recess / groove on Gie-Tec rails. So yeah, why not.. And it’s kind of a nice convenience thing to have the inside of case lit when you install or rearrange modules :)

I installed three 1 meter strips total; one behind front panel, one between the rails in the middle and one on top rail.

LED strip testing

The LEDs are powered off of the negative power rail. With eurorack modules this rail often has lesser load on it, so using that for LEDs will (kind of) help balance the rails. Pending improvement is to have a on/off switch on the front panel. The LEDs do add up to the heat inside the case a little, so it’s nice to be able to switch them off.

Homestretch

The final tasks of the build involved making outer side panels and a eurorack utility module to patch ADA8000 outputs.

The outer side panels I cut from 18 mm pine board and then treated both using water-based charcoal / dark grey stain. To have some substitute for the front panel handle I also added these heavy duty road case handles. Not the prettiest of solution, but the handles are sturdy enough to even lift the whole case upright (using only one handle).

Outer side panels cut, test-fitting handle.

Outer side panel installed

The ADA8000 output module is a simple 8-way unbalanced XLR-to-minijack thing 4 HP wide. I didn’t really bother documenting it, but let’s just say that the wood oil treatment turned out pretty nice! :)

Wow that was a lot of work!

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