E.S.V. Fuzz Germanium Version
The BYOC E.S.V. Fuzz (Germanium Version) kit comes with a pair of hand selected NOS AC128 Germanium transistors.
Q: What's the difference between Silicon and Germanium transistors?
A: Germanium transistors are what were used in the very first Dallas Arbiter Fuzz Faces. The original Fuzz Face used NKT275 transistors made by a British company called New Market. The NKT275 was New Market's version of the AC128. At the end of the 60's, Dallas Arbiter began using BC108 transistors instead. Germanium transistors have a slightly darker, warmer, and woolier sound. They can also "clean up" with the guitar's volume knob much better than silicon transistors. Silicon transistors have a little more gain, sustain, and brightness. The typical example of famous recordings that compare the two are early Hendrix (Experience) vs. later Hendrix (Band of Gypsies). Most people prefer germanium. The people who prefer silicon are usually going after a very specific tone such as Hendrix on Band of Gypsies, or David Gilmore on Dark Side of the Moon. One big advantage of silicon (or perhaps a better way to put it is a big disadvantage of germanium) is that its gain does not fluctuate with temperature. The gain of germanium transistor will increase as the temperature goes up. They become essentially useless in any settings that are warmer than room temperature. Silicon does not have this problem.
Q: What's the difference between the BC108 and BC109C silicon transistors
A: The BC108 is the traditional silicon transistor for the Fuzz Face. These were actually only made for a very short period of time. The trademark "Fuzz Face" has changed hands several times and there have been several reissues. One of the most sought after reissues is the BC109C version produced by Crest Audio. The circuit remained exactly the same as the original, they just used higher gain BC109C transistors. The BC109C version has a little more fuzz, a little more sustain, and a little more treble, but it also has a little more noise.
Q: What's the difference between PNP and NPN, what's the difference between positive and negative ground, and how will this affect my power supply?
A: If you don't know what PNP and NPN are, you don't really need to worry about it. It just refers to the polarity of the transistor. PNP transistors lend themselves better to a positive ground and NPN lend themselves better to a negative ground, but as with most rules there are always exceptions. The original germanium Fuzz Face used PNP transistors and had a positive ground. The silicon version used NPN transistors and had a negative ground. Positive ground means that the sleeves of the jacks, the chassis/enclosure, and ground of the circuit are all connected to the positive terminal of your power supply. Negative ground is the same thing, only everything is connected to the negative terminal of your power supply. Positive ground effects were more common in the 60's, but today, the overwhelming majority of guitar effects have a negative ground. Almost all DC adapters and power supplies that are intended for use with guitar effects have a negative tip. It makes ABSOLUTELY NO DIFFERENCE if you build your BYOC E.S.V. Fuzz kit with a positive or negative ground with regards to the power supply. The adapter jack of your pedal will still always be wired for a negative tip. This means that you can use any standard negative tip guitar power supply with the BYOC E.S.V. Fuzz kit regardless of whether it has a positive ground or a negative ground. The only thing you cannot do with a positive ground pedal is use a daisy chain power supply (such as the 1-Spot) with other negative ground pedals. You can use a daisy chain power supply, but all the pedals that share that daisy chain must all be positive ground as well. You also need to be careful of power supplies like the Dunlop DC Brick. It may have multiple taps/outlets, but they are still all daisy chained on the inside. Only power supplies with isolated outputs can power positive and negative ground devices at the same time. If you're not sure whether or not your power supply has isolated outputs, it probably doesn't. It's a feature that the manufacturer would probably want to tout and you pay extra for it. If you want to use a DC adapter power supply with your E.S.V. Fuzz kit, and you built it with a positive ground, the best thing to do would be to get a single standard negative tip wall wart (like the BOSS PSA series or something similar) just for this pedal. Chances are, it will be your only positive ground pedal.
UPDATED VERSION: This version has been updated so that the PCB can be built with a positive ground for PNP transistors or with a negative ground for NPN transistors. All you have to do is add a pair of jumpers. Note that if built with a positive ground, you DO NOT need to use a special power supply. You can still use any standard negative tip "guitar" power supply. You just can't daisy chain it with other negative ground devices.