Interesting, but I'm having trouble finding anything about how they work. One pot leaves no means for independent control over the key parameters. That's why I arrived at active, and have been referring to my project as "rewinder": it can duplicate the effects of changing the number of turns of wire, the wire awg, internal capacitance, and magnetic field strength.
Thus far nothing has turned up from searching patents, or even checking with people I know from other forums who would gladly dissect and study a $90 pickup.
Since you've mentioned that you don't have much of a technical background I can break down the really important stuff into pretty simple but totally effective terms. Depending on how ready you are to really dive in, it's worth getting a basic digital storage oscilloscope that has a built in signal generator. For pickups I have a handheld DSO 203 Quad from Seeedstudio running custom firmware and a wrote a program for the sole purpose of profiling a pickup within a few minutes. If necessary I can even turn volume and tone knobs up all the way, select the pickup I want to study, and then plug in a 1/4" jack directly into the guitar that is hard wired to leads from my scope. If you get one, I would be happy to share my code with you or anyone for that matter. You just select the range of the frequency sweep as well as the number of steps, press start, and when it's all done you'll have frequency and phase angle data that can be studied in any spreadsheet. I'm working to further refine it, but it's proven itself thus far.
Now, back to the original topic. In the simplest of terms all that matters for a passive pickup are:
*Wire AWG
*Number of turns of magnet wire around the bobbin
*Magnet strength
We won't worry about nitpicky stuff such as eddy currents, permeability, etc.
Wire AWG plays a major role in inductance (resistance as a function of frequency, and much more useful than DC resistance), and capacitance. Some people just go with the most readily available and "standard" magnet wire used for pickups. I personally prefer to maintain coil geometry so that the same approximate area under the strings will be as close as possible to the family of pickups I'm replicating. For example, you can fill a Strat bobbin with a few hundred turns of 34awg wire and drop the inductance and capacitance to insanely low values but this applies through a wide range of combinations. Even Amazon has a huge selection of magnet wire aside from the typical 42awg stuff that is normally used... But what you're doing isn't normal, so why worry about getting outside the box?
More turns means a bigger signal, but it also comes at the cost of capacitance. That's exactly the reason overwound pickups can sound muddy. A really great example are Fender's Texas Special pickups. They got to conduct a complete study of SRV's Number One and by all accounts the pickups were just what one would expect for a late 50s/early 60s Fender wind. To anyone seeking a vintage Strat tone, don't be afraid of DC resistance in the 5.5k to low 6k range. They sound fantastic. SRV used long high capacitance cables, but approximating his tone by including a 50' cable with every guitar that uses them wasn't an option (I'm sure marketing played a role here)... So instead, they overwound them to all hell so players who just want that one tone while using a high end 10' cable will probably get what they were looking for. Just don't ask them to deliver any spank or sparkle.
Magnet strength does interact with the coil, but as I said above we might as well start basic and can work up from there. They basically define the Q of the response curve, which is a measure of resonance. Stronger magnets will generally result in a much higher peak at resonance, and weaker varieties will be more mellow. If you want to visualize this: google "2nd Order Low Pass Filter". Fender has actually done a really good job with their vintage sets in terms of matching resonant frequency, but most of them would benefit from about a 20%-40% decrease in strength. Contrary to popular belief: AlNiCo V magnets, which are what Fender tends to use, don't lose much strength over time. After all, does anyone ever complain about the tone Hendrix got with brand new CBS Strats? Unless heated to temperatures that would destroy the guitar and pickups, even pickups from a 54 Strat or PAFs have lost less than 1% of their original strength. It's much more likely that the observed difference in magnetism is the result of modern manufacturing techniques resulting in higher quality magnets
Feel free to shoot me a PM anytime. You're going with a challenging route and I'm curious to see how far you can push it. You might also want to check in on the music electronics forum where their are tons of winders with all levels of expertise. And much like OLF, an overall friendly and helpful bunch.
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