The following is a summary of several previous articles. Think of parts 1-4 like the first book in a long series, and this as the prologue and first chapter of book 2. We've come a long way together and before we go any further it's time to take stock and see where we actually are before attempting any progress towards the next milestone (more on that towards the end).
Where we are
Guitar pickups are essentially inductors, and it is therefore possible to use a stack of PCBs with concentric traces as a pickup. Typical guitar pickups have an inductance of 5H, a resistance of 5-10kohm and some capacitance, usually picofarrads in magnitude. W have calculated the resistance and capacitance of a stack of PCBs to be 2.4kohm and 0.7pf per coil. Inductance is much more tricky to work out, and it was empirically determined to be roughly 10H, however upon revisiting some of the calculations ad trying a different method of accounting for the concentric nature of the coils an inductance of 5H was obtained. Ignoring any mutual inductance leaves us with an inductance of 0.25H.
Due to the differences in parameters, an active preamp is a good idea, the design of which will follow in a later article. Such a preamp would also allow the large range of possible inductances to be accounted for.
Active guitars are however not without their problems, and a large number of these involve batteries running out. As a solution to this I have proposed a novel circuit that makes use of relays and some clever jack wiring to enable external power to be used in conjunction with a battery.
Where we are going
The next stage of this process involves two sub stages. Firstly, in order to give us something to aim for, we should measure the frequency response of a pickup we like. Secondly we should design a preamp based on our coil parameters that would allow us to get a sound close to that. The second Stage will make use of simulation software such as LTSpice to reduce the number of physical iterations. Unfortunately due to the wide variance in capacitance a lot of the tuning of the circuit will have to be done by ear, however this won't be practical until a rough topology has been figured out.
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