Go to the Bottlehead site, and forum for the Crack.
Several things to read:
1st the FAQ: Crack FAQ
Then this little advice:
Since I bought my kit a few years back things have changed abit, but not much…but still small changes for the better. You should have all these incorporated in the latest manual and parts.
Get the Speedball upgrade, but dont intstall it without getting the base kit up and running well. Listen for a few weeks to get any idea of what the base sounds like, bass etc…then you will have a good idea what Speedball adds etc…
The third item in the FAQ is one that most Crack addicts install…it makes volume so yu have to turn up the vol pot more to get more travel and get out of the lower imbalance part of the pot…when you get a chance its a good upgrade to install a nice authentic ALPS pot. The original is fine, but its a low cost part and to keep the kit price down etc…many install the ALPS or even a stepped attenuator…IMO not necessary but the ALPS makes for a buttery smooth vol adjustment and the ch imbalance which I did experience always bugged me…but again build the stock Crack before you do this…then many of us can help u with the pot mod if u want to go there.
There are many mods, but most dont really improve things much more than the basic kit (not counting speedball)…but its an experimenters dream…
Doc at BH came up with the Crack-a-two-a which is really the way to go if your a modder, the basic crack circuits been around for ages and works very well as is…except for the pot upgrade all others are ok, but sonically well …your wallet will get low…better to get a Crack-a-two-a…
But that said a Crack w speed is just plaine sublime!
Tubes is the big thing for folks and lots of options but again its really a rabbit hole…
You wont know what tubes you will get until you get the kit!
I got a tall RCA 6AS7G coke bottle and a RCA 12AU7A…and still after spending $$$$ I like this combination very well…listening with it right now.
One last thing, take your time, read, and re-read the instructions, measure twice before cutting wire lengths, I hope you know how to solder well…this is the number one issue with most kits…cold solder joints, shorting out parts etc…the kit uses solid wire not stranded to avoid shorts…
Any questions or issues the forum at the BH site is wonderful and Doc and Paul Birkland will assist and answer your questions!
Good Luck!
Alex