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Your description fits what I am getting, but I don't see why. If the problem has to do with a circuit that does not let all the signal through, should it not affect all frequencies equally? My limited understanding tells me that the signal that gets through would be just lower in amplitude. How is it that some frequencies are affected and not all of them?



When first encountering Electrical Theory, we start with DC analysis.

That is a good platform, but when we must deal with Alternating Current, there are a few other parameters that rear their ugly heads and must be dealt with. Capacitance Reactance, Inductive Reactance and also Resistance work together as literal filters at frequencies that are dependant upon the values of the three.

In the case of the electromagnetic guitar pickup, we have all three.

Capacitive Reactance may be the lesser of the three here, but any amount must be plugged into the equation.

Inductive Reactance is there, due to the fact that the pickup itself is a huge coil of wire sitting in a magnetic field.

And, of course, the Resistance, which not only includes the input impedance of the following amplification stage, but also the resistance of the pickup wire, the cable in between, any potentiometers in the circuit, such as the Volume control, plus there is the potentiometer-plus-capacitor used in the Tone Circuit, which is another example of the LRC Inductive/Resistive/Capacitive tone shaping circuit, in this case a "Passive" Shelving EQ.

Those three parameters are related by pi, BTW, which assumes a sinewave.

Change any one parameter and you change the response of the circuit, in this case the amplifier input impedance being the main paramater that has changed -- and changed by many orders of magnitude, no less.

That 220K input amplifier would be a good choice but not the other one, which is too low. 220K would likely load the pickup down "a bit" but not so much as to greatly truncate the frequency response curve.

AC is a different world from DC theory and analog audio is Alternating Current. The AC is not locked to one frequency, but rather changes almost constantly, to become the "music" that we hear. That constant changing of frequencies is also a dynamic that can confuse even the most rapacious of "plug and chuggers" mathematics-wise, but not insurmountable. Plenty of info on the subject on the web if you want to dig deeper. And I encourage that.


--Mac

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