hey battleminnow,
about the first ten years out of College (BS in EE), i built all sorts of stuff, i duplicated a MXR Distortion+ (actually traced the circuit board), i built an
MXR Blue Box (again i traced the circuit), modified all of my effects boxes to use an external power supply instead of a 9V battery, i designed a Noise Gate, a Compressor, rebuilt my 60's Bandmaster amp and boosted to 100 Watts, designed a 8 effects computer controlled guitar switcher (before the Bradley). about a year ago i refurb'd my Fender BlackFace Champ and Princeton Amps.
the Princeton had a Power supply Hum that just about drove me crazy. this is a case where having new parts is no insurance of fitness. i bought a Marshall JCM-800 and changed the output tubes from 6550 to EL-34.
i read everything i could get my hands on. here's some of the literature that i still use today:
National Semeiconductor reference Books. National's got some very good Audio reference books
Burr-Brown reference books
Crystal Semiconductor
Radio Shack had a great book on circuits "Engineers Notebook" Cat No 276-5001. i don't know if this is still available
Electronic Filter Design Handbook
IC Master (A Must)
here's some circuit designs that you'll need to master:
filters with OP-Amps (Analog filter design)
power supply design (Very important)
types of resistors (Carbon, Metal Film...) and when and where to use them
types of Capacitors (Tantalum, Foil, Polyester, Metallized Polyester, Electrolytic, Paper, Polar, Non-Polar) and when and where to use them
Op-Amps
Tubes (a different beast from IC)
Analog Balanced Input and Output
Interfacing Digital with analog Circuitry and Power supply design
Digital (CMOS, TTL, LVTTL)
here'e some tools of the trade:
a good Volt/Amp Meter (I recommend a FLUKE)
an Oscilloscope (a must)
breadboarding equipment
a lot of small jumper wires
a very good soldering iron
a head warn magnifying glass
a stock of resistors, caps, some inductors, power supply transformars, IC's (Analog and digital)
someone to rub your back and neck...
and most of all
a lot of patience...
for me this was all a lot of fun and it's a skill and knowledge that sure does come in handy all the time. but, it took many years of tinkering.
good luck.
-keith-
) and parameter tweakability. General Midi is still much with us and digital delays, reverbs and all the rest are just no longer based on 8-bit converters like the projects I used to build! Hell, even my fuzz box has gone digital 
It used to be transistors driving my sine wave into a square shape.... but at least I learnt the basics of signal processing... 
