After some waiting and a few false starts, the Crack has been completed. It was done over three sessions. Firstly, I must say that the instructions and build went very smoothly. The instructions provided by Bottlehead is first rate. The photos included were first rate, and I used them mainly to do the work and to check the work. The written instructions are very clear, but I found them actually a little verbose and the layout could be improved. In addition to the Crack, I also purchased the Speedball upgrade and completed that at the same time. The one and only problem was I soldered the wrong Transistors on the Speedball update. I did not pay attention that there are actually 2 types of small transistors.
The only other initial upgrade I applied was to change the output coupling capacitors from the supplied electrolytic to a 100uF Aeon paralleled with a Russian K40Y 0.1uF. The caps are big and was a little tight to fit, but it does. After the above fix, the amp fired up without problems. The voltages and resistance all measured as per the kit.
The first session was with my usual setup, using source from an old iPod. On first impression, the bass is really present and in your face. Almost to the point that can be felt. Amazing. The sound was very good indeed. There was a slight amount of hum present, but its level is quite low, and I didn't hear it until I looked for it. Otherwise, the dynamics are quite awesome and was really an enjoyable listen. This was more impressive given that it was unbroken in and it was using 'standard' components like a stock attenuator, connectors, and electrolytic caps!
Having a quick comparison with my Mini Max Millet left a few impressions. The bass on the Crack is much better to my ears. More body and more present. The sound is more lively and seems to be more 'dynamic' and less compressed. As I run the amp in, in the coming months, it will be very interesting to compare this with the other headphone amps.
It is also time to dust off my Maple Tree Audio Ear+ and fire that up. In tandem, I also purchased a TubeCAD 9-pin all in one, with the intent of making another headphone amp with that. So in the next year or so, I will have supposedly four quality headphone amps to compare!