{To view the image folder, scroll down to the bottom of this post}
This will be more about the build and assembly of the Mainline versus an in-depth and exhausting review of the Mainline's performance. I think that is best described on this review, which I'm sure you've seen if you're looking on this thread. If you haven't.. go there now!
I read up as much as I could about the Mainline from different sites, but there hasn't been much talk about actually building it. This is only my second DIY build and I don't know much about upgrading components on a DIY kit, unlike like other posters on different forums talk about.
I'm using these builds as a way to enjoy a productive project with a satisfying sonic outcome.
Thoughts on the project:
HOW DIFFERENT/DIFFICULT IS THE MAINLINE BUILD FROM A CRACK?:
The Mainline is still possible to assemble if you've never done a DIY build before. With that said, I hope you know how to follow directions well. If not, then I would recommend trying the Crack before taking a crack at the Mainline. This is several steps ahead in complexity to the Crack build.
The Mainline incorporates a handful of new 'techniques' that the simple OTL design of the Crack doesn't include.
With the Crack, you have to do a LOT of wire cutting and stripping, then point-to-point soldering from one terminal to another. There is also some three-braid wire twisting, which I don't think the Mainline has. Not so far in my build, at least.
Outside of those issues, it's basically following along with the instruction guide. With the Speedball upgrade, you have to solder resistors, capacitors, and other goodies onto a PCB. This provides a new kind of challenge, because the solder points are much smaller and it requires more concentration to get each detail in the instructions done right.
With the Mainline, there are some new things to learn:
- More in-depth PCB soldering dynamics.
Due to the four total PCBs, along with the heavy-duty capacitors and interesting methods for twisting resistors and transistors, the PCB soldering process becomes more tedious.
I thought it was pretty cool slicing off pieces of a transistor and using that remaining wire to connect certain points on a PCB. I thought staples and/or separate wire would be used, but instead spare parts became cannibalized and utilized in a helpful manner. (see this pic as an example, at points 'D2' and 'R1'). Cool!
- Cat5 shielded twisted pair (STP), and separate STP cable use/installation.
Cat5 cable is what is used for internet cable. It comes in 4 pairs of twisted cables (thus the name), in a certain color sequence. IT geeks will know there are two color standards, but that's beside the point. The 'shielded' part is an aluminum wrap around the wires. This shields the wires from electronic interference, and allows for a quieter and/or more proficient performance.
With the Mainline build, you have to separate the twists, cut off certain named wires and attach them on the chassis and to certain termination points. It's kind of tedious, but I found it to be pretty fun. :P
- Assembling fine and course attenuators.
There is a piece of paper with numerous resistors at certain ohm ratings which need to be bended, twisted and applied onto the volume knobs in a particular sequence. the work going into this process takes time, but the instructions are very good and if you pay attention you'll have little trouble putting it all together. But it looks awesome!!
- Flips, switches, XLR and output transformers.
Obviously an OTL amp doesn't have output transformers (OTL stands for Output TransformerLess). The Mainline has two output transformers. Soldering/incorporation is fairly simple for the most part. It's fun to see more 'stuff' that was put into the build, though.
With all that said, I'm not done with my 'journey' yet. This isn't a 7-10 hour project like the Crack. I have already spent about 13-17 hours on it, and I am about 50 pages into the 78 page instruction guide. I don't now how much more time it will take, but I'm going VERY SLOW and deliberate with the build. I had one or two incomplete solder terminals in the first build; some ugly 'hangers' at the ends of terminals that weren't snipped; and LEDs that were not completely straight as well as some items on the PCB that were not as beautiful as they could have been.
With the Mainline, I am trying harder to make it a much CLEANER build. Not just because my soldering and understanding of the process has improved, but because there's a lot more going on with this assembly. That means, there is more to MESS UP during the build. I would prefer to read instructions 4 times, and take 5 times longer to solder a point and check if it's a solid solder. It would be a lot more difficult to troubleshoot the Mainline than the Crack post-build.
RECOMMENDED SECONDARY TOOLS USED/NEEDED FOR THE BUILD:
NOTE: This section is for someone who doesn't have regular amp-building tools in their repertoire. Very simple and obvious info for veteran builders. These items aren't too expensive, but it helps with assembly in a BIG way.
- Screw, nut and washer separators. There are a lot of screws and nuts, so it would help a lot to look at the inventory sheet and label which container has what kinds of screws, nuts and washers. I have a PC repair kit with a separator, but anything with 7-10 different places to put the parts into would be fine.
Assembling the hardware (the top of the chassis) is the first section, and once that's done there are far less screws and washers to worry about. I found having them separated beforehand was a lot of help, though. I counted the inventory and knew where to look when I needed them.
- Third hand/Helping Hands. I didn't have one in the previous build because I lost it, and it would have been helpful in some tricky parts. This time, it has helped a LOT.
The hardest part is remembering I can use it. It's like playing a game and getting an Uber ability, but you keep forgetting to use it in a crunch. I got in the habit of fighting and swearing a wire to fit into a tiny spot before soldering and praying it wouldn't fall down/slip off before I burn it in place, but the third hand just holds it there.
- Different types of solder thickness.
I use thicker solder for the actual terminals, because it's easy to cover the whole terminal quickly. For 'terminal' solder, the size is .062' diameter.
I have 22 gauge/.032' solder for PCB work, and for the output/volume/ohm switches. You don't want that thicker stuff for the tiny spots. At least two kinds of solder thickness adds convenience. Check out this pic as an example of the precision thinner solder provides.
- Solder-sucker/desoldering pump
It's only a few dollars, but man it's great. Heat up excess solder and/or a messed up solder joint, and then 'FWOOP!' - vacuum that mess right up. Keeps things clean!
- Flush Cut wire cutters
I did not have these, because I thought my regular wire cutter/needle nose pliers was good enough. Heck no! I like these for two reasons. 1) They cut off dangling ends of wire tips like no one's business, and 2) it makes it easier to see - after slicing - if all those wires in a terminal are properly soldered. I realize now, though, that you don't have to cut completely flush to the solder point. Leave a little bit of the leads poking out, or you could end up removing the solder as well and it will not function.
It seems like some people have enjoyed looking through my Bottlehead Crack thread, so I went more into the assembly process with this post in case someone out there was curious. I included a few details on assembly that I never read in other posts/threads/sites that I think I would have liked to know about beforehand.
I will make edits to this post and future replies/updates when I have the time.
Now, for pics:
Click here to see pics of the assembly.
I will add more photos to the album as I keep building.

I purchased a Bottlehead Crack amp, which has high ratings and is supposed to mesh well with the Sennheiser HD 650s, which are one of my favorite headphones.
I got the parts over a month ago, but I've been really busy. I sat down on Saturday and put it together. Took about 7 hours total. It was a lot of fun for me, and I enjoyed almost every minute of it (I did swear a lot when I had to place two LEDs into the 9-pin tube socket. That was a stinking P.I.T.A.).
A friend of mine builds amps, and so once I assembled/soldered everything, I checked the ohm resistance at the required points myself. However, checking voltage was something I've never done before, so I didn't want to electrocute myself and I sent the rig to his place. He said the solder points were great, and there were zero issues with the voltage checks. So I plugged in.
It sounds great! Not 'amazing', but I said 'woah'. That's the meaning for 'nice!' but it didn't make me go 'WOW!!'
I also have the Speedball upgrade kit, which I will most likely assemble in a week or two. I want to give some time with the 'stock' build to get used to the sound, and maybe I'll notice the difference when I upgrade.
Overall, I'm happy with the amp. It DOES sound good with the HD 650s, and I can't wait to try it on my other headphones as well sometime soon!
And now pics:
It started with just the aluminum chassis and four wooden blocks.
The power supply and audio/power jacks installed..
This is just the labeling process for installation, after placing in the audio jack, headphone jack and electric terminals for the wiring:
A closeup on the soldering job:
Took a short break with a Brew Dog to keep me going (but it took me over a half hour to drink it):
The build was pretty much complete at this point:
Completed, untested and before installing the tubes:
And finally, I started it up and here's the final product sans wood finish/glue for the case:
Conclusion: For the price, it really is worth it. I still have a lot more audio testing to do, but I am already impressed. It didn't FLOOR me with quality, but once again it certainly provides the juice and the punch when played with my HD 650s.
I am looking forward to spending some time with this, and then installing the Speedball upgrade. I wonder if I'll even notice a difference.
Either way, I really had a good time putting it together. I want to do something ELSE now, but I don't really have the time or the money! hahaha