Project Science Of Electric Guitars:
Having made a "guitar" (wire under tension), "pickup" (coil and a magnet) and a "speaker" (kitchen foil in a magnet), and proving it all works with a commercial amp, there was only one element left: building our own amp
So for the last 3 weeks the student has been learning to solder and has put together the simplest amplifier circuit I could find: 2 inputs, 2 outputs, one each of resistor, capacitor, transistor. With guidance, but doing it all themselves.
@_thegeoff Is the capacitor in series with the input or somewhere else?
Unless the transistor is a FET, I don't see how that can work with a single resistor (I expect a resistor in series with transistor's base is needed, as well as a resistor that will allow the capacitor to both discharge and charge).
@robryk Yup, cap in series on the +ve input, then to the base. Variant on the first circuit here: https://theorycircuit.com/audio/simple-single-transistor-audio-amplifier-circuit/
Just a proof of concept rather than anything particularly practical: remember, this is the world's worst electric guitar, the speaker is kitchen foil and croc clips :)
Ah, so it assumes that the input signal can only source quite limited current (otherwise I'd expect the transistor to potentially get blown by high current during turn-on transient: there's nothing in-circuit that limits the inrush current through input, capacitor, and transistor).
Ah, right, if the input voltage is below the junction drop voltage of the transistor the sourced current doesn't matter at all.
(I once wanted to detect mains voltage via an optocoupler and blown it in, I think, all possible ways due to transients while arriving at something workable that wouldn't continuously dissipate a few watts into a resistor.)
@robryk Exactly, we're twanging a wire in high school magnets, millivolts at best.