The Definitive NOOB Guide to Building an Amplifier Enclosure out of Wood

Let’s make a gravity mounted enclosure for an amplifier. Usually this is for a tube amplifier, but it’ll work for anything. If you’ve seen a Bottlehead Crack, you know what a gravity mounted enclosure is.

So purty. Let’s make one!

The wood base is called a skirt and the metal sheet that the components ultimately are mounted to simply sits on top of it. Gravity keeps it in place, though taking a bit of time to secure it to the skirt with screws is a good idea. We’ll focus on the wood part – creating a nice top panel by hand is another post entirely.

Before we get any further, we have two important lists to talk about. One makes sure you are not wasting your time and the other is so you can reasonably do this and, thus, not waste your time.

What you should expect:

  1. It will not be perfect. Things will be cut incorrectly, things will be a millimeter or two too long, too short, or of the incorrect slope. You’ll miss a tiny bit of wood glue and it will show through the stain. Accept this will happen.
  2. You have to want imperfection. If you are the person that cannot work with imperfection, you want to just buy something from a company where a machine does it.
  3. It involves time and a lot of waiting. Days worth.
  4. You will make mistakes ranging from “oh, that’s kind cool” to “Eh, I think I can work with this” to “shit, time to go back to the lumber yard”.
  5. You need to have sane tools. You can get away with really basic tooling but the crappier your tools, the crappier your end product and the worse precision you’ll end up with. However, embracing those imperfections will go a long way to a unique and awesome end product. But, no way around the shit tools and shit product correlation.

What you need:

  1. A miter saw. A miter box is probably gonna suck, I do not recommend it. I also do not recommend a hand miter saw. I’ve tried that and found it difficult to get accurate angles, especially if trying to put together a skirt requiring angle cuts.
  2. An orbital sander and sanding block. You might be able to get away with only a sanding block, but say good bye to more time and very sore arms/hands.
  3. A quality caliper.
  4. Wood glue, any will do.
  5. Wood screws (optional, dependant on the kind of skirt)
  6. Wood dowels (optional, dependant on the kind of skirt)
  7. Stain, get a few different stains and test them on scrap to see what looks best to you. I like Minwax Early American as it looks great on a variety of woods. A small can of stain will go a long way.
  8. Some sort of finish. Shellac or spray-on polyurethane are my go-to. Spray on is going to produce superior results vs. trying to brush it on, unless you’re way more talented than I.
  9. A drill.
  10. An electric screw driver (be nice to your hands/wrists and get an electric one).
  11. Painter’s tape.
  12. Clamps (at least 4 long-ish ones, more the better).
  13. Angle clamps (at least 1 of them, more the better).
  14. A speed square.
  15. A drill press.

That’s the sane list and if you don’t have that stuff already, you’re putting up a decent cost up-front. I consider that list to be the minimum for a decent product. You can get a lot of other things that will help and increase the awesome-ness of the finished product, but are not necessary IMO.

A tale of two skirts

There are two skirt designs I like. The first is a box of 4 equal length pieces of wood with 45 degree angles on each end that fit together to create a box with seams only at the edges. This creates a very clean and classy look. If your metal sheet is 12″ x 12″ and 1/2″ thick, you’re looking at 4 pieces cut to 13″. The downside to building this is that if you’re not able to cut accurate angles, you’ll have issues fitting it together nicely at the end. That is work-around-able depending on how mis-aligned it is, but that’s the biggest risk. We’ll call this the Pretty One™ and is the configuration Bottlehead uses. I’ve used it a number of times and it looks great. It’s probably the most popular skirt DIYer’s make.

A “small” tube preamp using a pretty skirt. Made of oak. This one actually kinda has some flaws, but still looks good to the non-insane.

The other consists of two lengths that are the length of two sides of your top panel and two that are the length of the other two sides, plus the thickness of the wood. So, if your same metal panel is 12″ x 12″ and your wood is 1/2″ thick, you’re looking at two 13″ lengths and two 12″ lengths. Seams on the sides, not the edges. This is easier to put together and will result in much more noticeable lines. There are also ways to incorporate decorative physical seaming or lines with this method. We’ll call this The Rustic™.

A Rustic™ mid-build.

Which method to use? It depends. If I’m looking for a more sleek look, the first option is the best. If I’d like to build something with lines and perhaps a more “worn” or “hand made” look, the latter is best. Both will produce a very sturdy and safe product, which is just as important as beauty.

DIY Audio Facts

NOTE: This is going to be regularly updated as I think of new stuff to add. Keep checking back.

I’ve got a few draft “how to” posts in the works, but I always feel the need to say a few things about DIY audio before each post. If that’s the case, I should just make a single post going over it.

One of the things any new DIYer will quickly realize is that making something yourself is not always cheaper than just buying something pre-built. Audio is no different. Do not get into DIY anything thinking that it is a way to save money, it’s the opposite. It’s a money pit, but cheaper than going to the bar.

With that out of the way, if you can tick all these boxes, congrats, DIY audio is for you!

  • Like music.
  • Like to problem solve.
  • Like to learn.
  • Don’t mind fucking up.
  • Do not already have a hobby that eats through your disposable income.

Cost is a thing

Yep, still going on about cost. It’s expensive and your cost breakdown for building a quality amplifier looks like this, from largest expense, to least.

  1. Enclosure ($$$$)
  2. Quality transformers/Chokes/etc… ($$$)
  3. Tubes/exotic ICs ($$$)
  4. Heatsinks/other metal stuff (if applicable) ($$$)
  5. PCB ($$)
  6. Good wire, switches, potentiometers, big capacitors, general other hardware ($$)
  7. Normal capacitors ($)
  8. Everything else – Resistors, LEDs, rando things, etc..

Things can move around and decisions get to be made – do I go with a cheaper Bourns potentiometer, a nicer Alps, or a super slick stepped attenuator? If a super slick attenuator, that could shoot up #2 on the list. If you’re building a tube amp, tubes could either be like $10 or hundreds or more. All depends. But you get the idea.

Most projects will include an estimate on how much it’ll cost you to build it in their Build of Materials. Pete Millett’s Butte is a little over a hundred including an enclosure. However, once you really start to customize things, it can get spendy quick. I’ve not even talked about the tools you’ll need to build something – that’s a whole other list and discussion I’ll get to at some point.

This is not about saving money, but building and enjoying the process and product. And it’s worth it.

Greg, Power Supplies, Dim Bulbs, and Not Getting Electrocuted

First, it’s been a while since I last posted. COVID-19 and all kinds of other personal, work, and other stuffs have been making it hard. I hope y’all are ok, well, and dealing as well as you can.

Ok, so after the O2 it all gets a bit hazy. It was around this time a number of projects happened, another Pete Millett amp, I think I built a quick CMOY for some reason, and probably something else – but I remember building a ESS ES9038Q2M dac from a board I bought from AliExpress. The particular board I purchased has lots of variants and there is an extensive discussion of that family of Chinese dac boards on diyaudio.com.

It was my first time actually building a power supply and using a transformer. This was scary. Things like grounding were no longer about eliminating noise but about safety and not being electrocuted. Obviously, this was scary and just reading about what to do on the internet seemed a bit risky.

My day job was working in tech. Much of the company was remote so we all used a chat tool called Slack to communicate. What was great about this is Slack allowed for various channels or rooms that were work related and whatever else you could want. Remote worker water-cooler chats happened in places like “The Danger Room” or “Pancakes”, the latter being a place to post pictures of delicious pancakes. One of those channels was dedicated to music and I had already started talking about amplifiers, dacs, headphones, and all that in there. I was likely being annoying to everyone who was there to discuss Taylor Swift.

But it was through that Slack channel I met Greg. Greg was in to DIY audio as well and was much more accomplished. He’d built speakers and power amplifiers – you name it, he’d done it. He had a crazy awesome home lab complete with measurement gear, a CNC, and loads of other goodies. He was not only soldering things together but milling aluminum enclosures and fabricating the entire product.

He is/was my idol.

Shortly after discovering we were doing sorta the same thing, we started a “DIY Audio” channel and, though I felt silly, started asking him questions about wiring for my dac. Windings, secondaries, center tapped – stuff I didn’t know about and he’d explain to me. I told him I needed 15V AC to the dac board, which apparently had a it’s own DC power supply. He showed me a R-Core transformer that would give me the 15V AC I needed and walked me through wiring it correctly, using a fuse, and where to ground things.

The enclosure I purchased was one from Hammond Mfg. and had some nice wood side panels. I’d take a picture, send it over slack, he’d say “the green wire should go to ground, twist those red/white and black/white ones together”, and it’d do it. Funny enough, if I’d just looked at the wiring diagram that came with the transformer I proably could have figured it out. However, since we’re dealing with AC electricity, I was scared to death. And death is possible.

He also suggested I spend some time building a dim bulb tester. What that does is lets you, relatively safely, test high current gear without a ton of risk of damage. If there is a short, the light bulb will light up and there shouldn’t be a fuck ton of current flowing through the gear. Now, a small dac is not quite super high voltage and testers like this come in to play big time with anything involving tubes, but AC mains are still involved and I didn’t want to risk fire, death, or any sort of bodily harm. I built one out of a wall electrical box and a plugin light bulb receptacle after a quick trip to Home Depot.

There were some things in the middle here – the board had mounted RCA jacks on it and I wasn’t sure enough of my ability to drill correctly aligned holes in the expensive enclosure, so I opted to de-solder them, panel mount them to the enclosure, and run wire back to the board. I did this and ruined most of the solder pads. This lead me to having to trace those pads back to their origins and attempt to solder the wires to those points. I did that, felt accomplished, and re-checked continuity with my multimeter at least 5 times.

Alright, the moment of truth. I’d drilled out the chassis I purchased with my hand drill (which probably deserves it’s own post), wired everything, secured everything, shrink wrapped any wires where something conductive could possibly touch or even move, plugged the dac in to the one end of the dim bulb tester, the tester in to a power strip in the off position, and inserted a light bulb. With fingers crossed and standing a more than a few feet away from the dac, I turned on the power strip.

A small LED lit up on the dac board. No smoke. I was still terrified.

Using a multimeter set to measure AC, I carefully touched the probes to the enclosure to make sure no current was flowing. They said none was. I flipped them to DC, touched one to the enclosure and the other to a spot on the board where I knew DC flowing. It measured the correct voltage. Holy shit.

So, at this point you have a few options. Keep testing various points to make sure things measure as they should or YOLO and plug something in. Because I live on the edge, I plugged in my laptop and beloved Butte. It worked. I heard sound, music, and no noise. Holy shit.

That dac was a lot of terrifiyingly fun to make. It was my first experience with a transformer. Thinking back on it, I could have just bought a 15VAC wall wart and went that route, not even dealing with the transformer, IEC inlet, and grounding would have been a lot easier. But it didn’t even occur to me. At the time I’m not sure I knew it was even an option.

Three things were learned in this build. I learned about transformers, windings, what a center tap is, primaries, and secondaries. I really met Greg and got to know someone who actually knew what they were doing, though I’m sure he’d say he doesn’t know. I also learned that anyone who says a dac makes a significant difference in how something sounds is full of crap. I’m sure there may be exceptions to that, but my experience with this dac, compared to everything else and the onboard dac on my computer, is they all sounded good. Or rather, was just there. Couldn’t hear a difference. I’d learn that as long as the actual analog stages (IV, gain, output buffering) of the digital to analog conversion were properly implemented, it shouldn’t matter.

So, just like Pete, thanks Greg. It’s been a lot of fun to have someone to almost get electrocuted with.