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Bottlehead Crack – “The Build”


I’ve been quiet for a while – sorry regular readers! But thanks for visiting while I’ve been away.

As a little reward, I have 4 awesome posts coming up in the coming days / weeks starting with this one…

The reason I’ve been absent is that I’ve been unwell. I’m making a full recovery, but have had some significant rest time. Of course, that’s meant lots of time to play with audio gear including the amazing new Tralucent Audio T1 portable amplifier and the Unique Melody Miracle custom IEMs which should be arriving any day now. I’ll have full reviews for you as soon as possible, but today it’s all about Crack!

I ordered the Crack amplifier kit from Bottlehead ( quite some time ago. The Crack is under large demand and they are basically packaged and shipped to order which means you can wait up to nearly 8 weeks (in my experience) before you get your hands on your kit. It worked out well because I got it just in time for some relaxing soldering while I rested and recovered.

By the way, I have absolutely no experience building electronics circuits. I am handy with a soldering iron (from many years of car audio installation and tinkering with speakers and hi-fi wiring), but can assure you that this is a kit that an absolute beginner could manage by applying some care and attention. There are also some great videos on YouTube about soldering including Tyll Hertsens from Inner Fidelity’s video of building this same Crack amplifier.


Some flaws in the lacquer coating the transformer body

The kit comes in a single box with all parts separated into clear plastic bags and a few smaller boxes. There’s also a CD included with the brilliantly detailed and clear instruction manual. All of my components arrived in perfect condition despite travelling all the way from Washington State in the USA to Melbourne, Australia. That’s to say there was no sign of shipping damage.

The corner of the plastic edging is broken, but is covered by the metal dome once the transformer is fully assembled

There were some minor issues with the supplied power transformer, but they are just cosmetic and not really a concern to me.

All-in-all, the presentation of the Crack kit, while simple, is great. It’s all there ready to get going the moment you open the box (and take a few moments to print the assembly manual).

The Build: Stage 1

The assembled underside of the chassis plate prior to any wiring

The first step in the build is to attach each component to the aluminium chassis plate. It’s a simple process as all of the holes are pre-cut for you. Some pieces snap into place (the switch and power socket) while other part require some simple screwdriver skills.

All up, the assembly took me no more than an hour (less I think). I wasn’t timing the process – I just know it was easy and fun and I was done before I knew it.

There is one fiddly bit where you need to create a thread in a couple of holes before attaching a series of parts (all part of the transformer pictured above) in one go. It’s fiddly because there is one set of screws bringing together multiple parts, but after a bit of juggling and some strategic use of sticky tape it all comes together easily enough.

The top of the chassis plate before any wiring

Once the assembly is done, it’s time to break out some tools including:

  • Soldering iron or soldering station (more on this later)
  • Needle nose pliers
  • Wire strippers
  • Wire cutters

I’ve read recommendations to also use “helping hands” (clips to hold items while you solder them), but I don’t have a set and didn’t find myself missing them.

The Build: Stage 2

The important thing about soldering the Crack is patience. There are lots of solder joints to create and some of them require checking and double checking. Failing to show patience could easily leave you with broken components that you may not be able to easily replace – meaning long delays while you order them online and wait for shipping.

I want to stress again that the process is not complex and the instructions are just brilliant. Novices can build this amplifier so don’t be scared off if it looks complex – it really isn’t. It’s just a nice step-by-step introduction to electronics. I had no idea of how each of the pieces worked in the circuit as I soldered them in, but that doesn’t matter. I now have some idea of what’s going on in there, but still couldn’t explain it to you in any detail. The lesson? You don’t need to understand the circuit to successfully build and enjoy this amplifier.

The first step in the process is wiring the power socket (photo above right) into the circuit. It’s a really nice simple way to start off. All of the solder joints are easy to access and short of melting the power socket or switch by overheating it, there’s not much you can do wrong.

You’ll notice on some of these images that there are numbers scribbled in black marker all over the metal plate. The assembly manual includes the instructions for this numbering and it makes soldering really easy – just connect the numbers and solder the joints when it tells you – foolproof!

By following the instructions and numbering system, the wiring came together over the course of a day – about 5-6 hours all up I think.


As I said, this might look complex, but the instructions are simple and it’s just one step at a time. That said, I did make one error. While soldering a couple of LEDs into the small white tube socket (centre, bottom of the image above and left) I managed to overheat the LED wire and melt the LED. Here’s the result:


The staff at my local electronics shop, Jaycar, looked at me strangely when I tried to buy a replacement of this somewhat specialised component so I came home and searched online to find a replacement. Thankfully I only had to wait a couple of days, but I had to buy 5 so I have some spares and no idea what to do with them.

Side note: At this point I also decided to buy a cheap (but not crappy) soldering station. This is a control box and soldering iron combined where the control box lets you choose the exact heat of the iron. It made a massive difference because it was generally easier to work with and prevented over-heating of components (like the busted LED above). I can’t recommend them enough for anyone looking to do a project like this. Mine was under $100 and well worth it!

A point worth mentioning here is the importance of getting some components placed in the correct way. See the silver stripe on the LED above? That’s one example (the black cylindrical capacitors in the other images above are others) where you need to get the components the right way around. Failing to do so may stop the system from working and could result in destroyed components. It’s just a matter of patience and care and the manual reminds you to check and recheck so it’s hard to mess up.

The Build: Stage 3

There are 2 steps you can do at the same time now. You can glue the base which comes in 4 pre-cut pieces and you can complete the testing of your freshly completed wiring.

The base is really easy to assemble because it’s just a matter of gluing and aligning the 4 pieces. There is a recessed edge where your completed chassis plate will sit so it’s very easy to line up and it can just sit in place as the glue dries because it supports itself. The assembly of the base took about 5 minutes plus drying time.

While the glue dries, there’s some testing to do. The manual clearly explains how to complete the testing which is done in 2 stages.

First you test the resistance in the circuit at key points. This is a nice low-stress series of tests because the system isn’t plugged in. The second stage requires a little more care and attention because it’s time to test voltages and that means connecting 120V or 240V power (depending on where you live).

Once again the manual is great at providing easy-to-follow instructions and provides plenty of warnings and tips to make sure you stay safe while you test the voltages.

If it all tests ok then you’re done – time to enjoy your new amplifier! Here’s mine all setup and glowing with tube-y goodness!

This is an enhanced shot of the Crack – the tubes don’t actually glow as brightly as it appears here.

A Little Trouble Shooting

I was a little disappointed when I fired up my finished Crack. When I plugged in my HD650 headphones there was a definite hum which got louder with the volume control.

By asking some questions on the brilliant Bottlehead Forum, I was able to get some help and understand that the problem was with my input wiring (the red, black and white braid down the right hand side of the image to the right).

The braid you can see in this image is designed to prevent noise being induced, but my braid mustn’t have been tight enough because it was picking up all kinds of noise.

I had 2 choices: redo the braid or think differently… I took the latter option and hunted through my cable box. What I found was a good quality RCA cable that I had made myself. I cut a length out of it and used the shielded cable to help prevent noise.

The reason I chose this option is that the RCA cable has 2 layers of copper shielding built into the insulation layers. In my mind this would provide much more protection against induced noise. The 2 layers of shielding get wound together and connected to the ground circuit of the amplifier. In theory this means that any interference will get picked up by the shielding and syphoned off to the ground circuit and away from the audio output circuit. You can see the layers of the cable I used in this photo:

Oh, and just to be sure I connected the shielding directly to the ground circuit. You can see the single black wire running from left to right between the purple shielded cable and the small nut which is the main earth/ground point for the amplifier circuit.

The good news is that this fix worked a treat and the amplifier sounds brilliant! I look forward to sharing a full review with you very soon!

If there’s anything else you’d like to know about building a Crack amplifier I’ll be glad to help. Just ask your questions in the comments section below.