First-time poster, BTW:

Goal: with ideally one component, a capacitor that I can experiment with after the theory is figured out, create an HPF inside the instrument. Assuming that the electronics within the instrument is very simple, a pickup and a volume pot, how do I calculate the desired capacitance? The capacitor would be placed directly between the volume pot and the instrument jack. Almost there...

In a simple High Pass Filter, a capacitor may be placed between the voltage source and the load. The cutoff frequency is f = 1/(2 * pi * R*C). I want a cutoff at 50Hz, so far so good, but what is the load (R) in this case? I'm assuming that the preamp constitutes the load. The specs of the preamp state an input impedence of 2.2Mohms.

If so, my calculation is 1.45nF = 1/(50Hz * 2pi * 2.2Mohms). Intuitively I would expect a larger cap, so I assume my assumptions are wrong. Checking a different preamp with an input imp of 500k ohms, I get 6.37nF, which is still in the same ballpark.

As a follow up question, what might I do to this design to create a steeper slope at that cutoff, like 24db/oct?

Thanks in advance!