Preamplifiers:

Preamplifiers are sensitive devices, and can easily be damaged by faulty currents from amplifiers or trying to hook up their battery the wrong way around, and some are just cheap and burn out, but they have been improving over the years.

There is little to repair on some preamps, as may be cast into a block of epoxy to make it hard to steal the technology, so when one fails, replacement is normally the only option, which can take anywhere from 30 minutes to an hour.  Active pickups have a built in preamp, and are constructed in the same way, and also need replacing when not working, so like other pickups it takes about 20 minutes to replace one.

Besides adding a boost of power where desired, and contrary to popular belief they are not just for power hungry metal heads, but can be used to widen the range of tone control significantly, by boosting selective frequencies, rather than just draining trebles to ground like passive tone circuits do.  They also allow for mixing and matching pickups of different types, check out the customization section to read more.

Shielding:

Shielding has only one function, which is to disallow transient RF (radio frequencies) from acting on the electronics, and coming through the speakers of your amplifier and recording gear.  RF can come from electrical motors, combustion engines (spark plugs), neon and fluorescent lighting and other sources, all wreaking havoc on your sound.

Proper shielding is the most common way of dealing with RF, but there are also ferrite beads used with active circuits to single out more specific frequencies of RF.

Shielding can also be over done and have undesirable effects, when done near and around pickups, as it can also influence magnetic fields.  Even though most components are shielded by construction including some wires, everything in between can still pose a problem, so shielding the control cavities can help a lot.

The real art of shielding is to quarantine everything in the cavity, because although RF is directional, the shielding under your Stratocaster pick guard is silly because you may not be facing the source, and without the rest of the control cavity shielded, you may have to play the game of twister to avoid noise.

Shielding can only be done with metals, and its effectiveness is not a matter of how thick the shielding material is, but how good the seal is, of course thicker materials stand the test of time better, and are harder to breach.  There is such a thing as shielding paint, but it is ridiculously expensive, hard to apply, can crack and crumble easily once dry, and has a short shelf life.  To top it all off shielding paint is volatile, no one in their right mind wants to breathe in the fumes, and it is not environmentally friendly.  I hate it, and don't use it.

Considering all the above, the best material for hand making shielding is copper, but it is not easy to work with where curves and corners are concerned, as soldering and folding is required.  I can shield any control cavity with copper by hand, but the time it takes can vary widely from 2 all the way up to 4 hours maybe more.  An alternative is aluminum foil, not the kind you have in your kitchen, but something thicker.  It is more forgiving than copper and can take from an hour to 3 hours for a cavity.  There are factory made shielding boxes for some common guitar models for purchase, but they go in and out of style and can be hard to find, but not to expensive, and can be installed in 30minutes to an hour, as some wiring must be undone and then redone.

Wiring:

Here is where a great many mistakes are made, by instrument owners, repair people and even manufacturers, as few understand the intricacy's of circuitry where waveforms are involved.  Weather there are bad connections, grounding issues or other problems, There are things to consider that escape most non electricians, and you can be assured that when it comes to wiring, I have few equals in this business.

When I wire, I consider everything from conductivity to strain relief, and there are silly sounding ways of connecting ground wires that in reality can make the difference in having buzzing or not.

I have had colleagues ask me if I were trying to wire a military tank, when they had to change a component on a device I had wired, but a good connection is best made before any solder is even applied, and the best sound boards in the world, and other high end equipment, use the same theory.  When it comes to wiring there are do's and dont's, depending on the frequency's in question, or you may end up adding an antenna without even knowing it.

Since most wiring is done during repairs and upgrades it is already part of that job, and doing it right hardly adds to the time it takes, so it is a good idea to have me re-wire the whole instrument while I am at it, as it only adds from 10 to 40 minutes and a few bucks in materials to the job.

A worthwhile addition:

If you have ever felt a tingling charge coursing through your body while playing guitar and touching a microphone with your lips at the same time, then you may consider yourself lucky, as this "ground fault" often leads to serious injury or even death, depending on the amount of current supported by the circuit of which you have become a part of. Since you can not rewire the venue you are playing at, nor the P.A. System, it only makes sense to have a life saver in your guitar.

For one dollar in parts, and only ten minutes of additional time on your repair bill, I offer a simple circuit, called a shunt, that will blow out before you do by cutting the ground to the bridge and strings.  Once blown, it can be replaced in under ten minutes, with the additional one you will find in the control cavity, which sure beats your band having to replace you.  I can also add screw terminals for quick replacement, just in case you gig a lot and encounter ground faults often.