With the guts of the amplifiers almost completed, the enclosure and all that comes with it is up next. And that’s a lot! Knobs, front-panels, materials, silkscreen, colors, designs and structural strength to name but a few. Since my amplifiers are completely ‘from the ground up’, there’s no off the shelf solution. And a simple black box with plain text just won’t cut it. I want the amp to look as good as it sounds.
Form factor
The headshell enclosure is synonymous to tube amplifiers, giving them an instant retro-look. And they’re roomy, so it’s easy to stow away all components. Unfortunately, they’re not my cup of tea. They tend to be big and bulky. Headshells are also harder to combine with other equipment. And the whole ‘retro’ thing is not the right feel for what I try to portray with the electronics and sound signature.
I’ve always been a fan of 19 inch rack enclosures. Their modular nature provides a perfect platform for building your equipment stack to taste. Being able to combine different amps and add-on effects, tuners, EQ’s and power conditioners always appealed to me. I’ve build the separate pre- and poweramp for this very reason; the ability to mix and match them with other gear how you see fit, depending on the setting and power requirements. Although they do form a perfect couple 😉
Two drawbacks to 19″ enclosures. They’re smaller than headshells, so it sometimes seems impossible to fit everything inside! Tube-amps use two transformers mind you. But more important, the aesthetics when they’re not mounted in a rack. Your left with useless mounting tabs on either side, giving them a somewhat industrial look. Again, not what I was going for. Best of both worlds; detachable rack ears. Rack mountable and still looking great when the amps are used ‘naked’.
Not just an empty box
The form factor for the enclosure was set. That was the easy part. Honestly, I underestimated the ergonomics and only started to think about the actual face and usability of the amplifier once the electronics were well on their way. Lesson learned. The various controls might follow the logical progression of the signal path, but we’re talking distance between knobs, knob height and symmetry, the positions of various buttons and how to visually separate the different sections. Since the front- and back panel layouts reflect on the circuit boards, the full set of PCB’s got a revision purely dedicated to the positioning of the potentiometers, switches, mounting holes and PCB shapes.
There are other aspects to keep in mind when shuffling the various components around. Instead of just cramming everything inside, it’s best to keep the sensitive parts of an amplifier well away from the ‘dirty parts’ like a power supply and transformer. This also helps with creating a grounding scheme(!) following this same paradigm. With care, you can reduce the noise floor significantly, specially in the 50/60Hz and 100/120Hz range. It’s no accident the power transformer is at the complete opposite side of the amp’s input.
Down to the actual electronics, the physical size of components is another caveat. 
Not that big of a deal in a 3-units high enclosure, but inside a 1 unit (1,75″ / 44,45mm) enclosure, you’re left with a ceiling height of 1,4″ (35,6mm) at the most. Minus PCB stands and thickness… capacitors and heatsinks will quickly become troublesome. Most electrolytic capacitors will come in low profile types though, increasing the diameter to compensate for the reduced height. The same issues arise with relais, connectors and foil caps. Something to keep in mind when designing for a low profile enclosure.
Rapid prototyping and ‘Maakplek’
I’m blessed to be part of a fast growing ‘makers community’ in my hometown, Groningen. It’s called Maakplek (Make space). It’s an awesome basement, filled with tools and equipment at your disposal which is either donated, crowd-funded or shared by other participants. But the best part are the people with an amazing range of skills and knowledge (and the willingness to share this) that tend to visit the ‘Maakplek’.
Rapid prototyping is one field the Maakplek facilitates. Lasercutting, 3D printing and small form factor CNC milling for example. Equipment I would never be able to afford all by myself, yet very powerful stuff when combined with today’s excellent 3D modeling software. Sometimes free of charge for starters (Autodesk Fusion 360) or available as freeware (Sketchup). I’m lucky to have a background in 3D modeling (think architectural visualizations and educational animations). This, and the fact that amplifier parts are pretty straight forward translates very nicely to modeling for e.g. 3D printing.
The point to all this is that using these rapid prototyping techniques, I made a pretty convincing mockup enclosure well before ordering the final version. Virtual models and renders are great, but there’s no substitute for seeing and feeling an actual part. The curvature of certain knobs, the contrast between colors in real lighting conditions, the distance between different control elements, let alone the ability to see if parts actually fit together in 3D space! I can safely say I’ve avoided many errors in the first metal prototype, saving me both a lot of investments and headaches.
From CAD to metal
Once all prototyping with plastic, wood, cardboard and old cut-up enclosures was done, it was time for the real deal. I am by no means a skilled metal worker nor do I aspire to become one. I found an invaluable partner in Protocase. Not only do they offer an impressive range of materials and finishes, but they also provide you with the tools to help you on your way. Protocase Designer is a proprietary software package aimed at the CAD-novice. It offers a ton of templates to get you started, which can then be edited to your liking. Creating cutouts, adding studs, nuts and standoffs, choosing the right colors, previewing silkscreens, you get the idea. The ease of use comes at the cost of advanced features like 3D milling or adding parts like custom brackets.
But, when your basic design is done, you can send them the files and ALL your extravagant ideas. Customer support really is second to none. They’re fast to respond and they will make sure your custom wishes will be met. Within reason :). I’ve had intensive contact with each employee responsible for a specific step in the production process. Each deliberation pushed the final product to a level I never thought possible up until a few months ago. They truly make the difference between an average looking box and a professional looking bass amp.
So close!
The above brought me to the point where it was finally time to ‘let go’ and make it all a reality. The enclosure is being fabricated at this very moment. I can’t wait to see it! Part 2 will focus on actually building the final version. What details did I miss and what remains to get it to a sellable level. There will be wood involved! And some parts still need to get anodized and silkscreened… Almost there. See you at part 2!
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