This is the bass I built. It wasn't exactly from scratch; I bought the neck, an unfinished body and some various other parts. The hardest part was really finishing the body. I HATE polyurethane finishes on any kind of musical instrument. The finish is overly glossy and hard, making the guitar feel sterile and killing some tone. Unfortunately, 99% of the guitars for sale at a place like Guitar Center are finished in poly.
Part of the appeal of vintage guitars, perhaps unconsciously, is their lacquer finishes. You can control the level of gloss on the lacquer by polishing it, and it usually ends up glossy, but not too glossy. Lacquer also ages very nicely; parts that are touched more often when played will be a bit glossier, and small dents, chips, and cracks from weather checking end up giving the instrument some personality over time. A beat up guitar from the '80's will never look as good as a beat up guitar from the '60's because hard poly finishes look awful when damaged.
So, part of my motivation to build my own bass was that bass bodies finished in lacquer are hard to find and expensive. I found a nice unfinished one-piece ash body on eBay and finished it in Surf Green nitrocellulose lacquer.
Finishing guitars is hard because you can't just spray the paint on. I spent about a week prepping the body by filling in all of the wood grain with grain filler, smoothing it with sanding sealer, and priming it, with a generous amount of sanding between every step. It took me a while to learn how to spray the paint so that it wasn't too wet or too dry. You have to do a lot more sanding if you miss either way. I spent many hours listening to my bar lectures and wet sanding the body. It was actually a good combination.
The neck is from Warmoth. It is made from goncalo alves with an ebony fretboard. The nice thing about the goncalo alves is that it is naturally a nice dark color and doesn't require any finishing. I like the feel of a raw wood neck.
The metal hardware is all used; I went for the rustiest stuff I could find. I like old things. I don't know why.
The bridge pickup is a hot split coil wired in series like a Precision Bass pickup while the bridge pickup is a traditional Jazz Bass pickup. This way, I am able to get both Precision Bass and Jazz Bass tones and it still looks like a Jazz Bass, which is the look I prefer.
The other thing I did was restore an Ampeg B25 bass amp. I got a chassis in pretty sad shape that had been removed from a combo. It didn't work. I got new tubes for it, replaced all of the electrolytic capacitors, insulated the case of the output transformer because it was arcing, cleaned up the electrolytic fluid on the board, and resoldered all of the suspicious-looking joints. It took me months to track down all electrical issues, and I was on the verge of giving up a few times, but I finally got it sounding good.
I built a cabinet for it out of birch plywood and covered it with Fender tweed, which I had finished with amber lacquer. It now looks like a 50's Fender instead of a 60's Ampeg. By the time I had finished it, I lost my taste for the 50's Fender look. I am now selling it; I never really got attached to it because it caused be so much frustration and my bass skills are not really worthy of it now that it's going strong.
One of my easier projects that I'm really proud of is my guitar amp. I bought a stock Epiphone Valve Junior head (a very cheap all-tube amp) on craigslist and a damaged cabinet with a broken speaker off of ebay. I read a lot about valve junior mods, and ended up going with mods that imitated a Vox circuit. The basic structure of the circuit remained intact, but most of the resistors and capacitors were changed to different values. I also added a "bright" switch which puts an extra tone cap parallel with a preamp resistor. I put a Weber Blue Dog speaker in the cabinet, which is a good but inexpensive imitation of the Celestion Blue speakers used in Vox amps. It now really sounds like a Vox, which is by far my favorite guitar sound.
My biggest regret of the summer is that my primary instrument became the soldering iron rather than the things that actually make the music.