I came to electronic music as someone with a lot of experience with computer & electrical engineering, at least at a theoretical and hobbyist level, but almost no experience with making music. Fortunately, music theory and practice is a heavily discussed subject online, and while electronic music isn’t always the focus of most resources, I’ve been able to learn a lot of things in that vein.
I don’t see much out there for “EE for musicians”; probably because, well, music theory and the techniques and practices of your craft are more important to the quality of your music! That said, I so often see people asking questions like, “is it okay to use a power adapter with too many amps?”, or otherwise saying things which demonstrate a lack of context around basic EE topics, and I would love to provide some of that context - so, here we go. I hope this thread can also serve as a place for people to ask questions.
To avoid a long physics lecture, I’ll just say this: there is a thing called voltage potential. We can measure it. If it’s different in different places, and you connect those places with a conductor (like metal or ordinary water), an electric current flows between them. Nature is “trying” to make their voltage potential the same.
Static electricity - that “zap” when you touch a car in winter - is what happens when some voltage potential builds up naturally. When you touch the car, you are connecting a high and low potential, and a current flows to equalize them, which happens quite quickly.
Batteries and generators are machines which do a good job of creating and maintaining a voltage potential between the two sides of the battery, or the two prongs of an electrical plug, even while a current is flowing.
This is the big one. Ignoring all other aspects of electronics for a moment, we have to acknowledge that all electronic devices - indeed, all electrical devices - require power to operate. We can think about voltage and current (measured in volts and amps) in terms of water in a pipe. Voltage is the pressure - how hard we are pushing on the water. Current is the volume - how much water is actually being moved.
If you think of your equipment like a water wheel, you’ll see that the two need to be matched to the equipment. Shooting a high-pressure jet of water at a mill won’t move it, but neither will an entire ocean of water that’s barely moving at all. The voltage needs to be high enough, but not too high, and there needs to be enough current available.
Considering this analogy, you might realize that to really understand what’s going on, we need to know something else: the diameter of the pipe, or the width of the stream. This is a quantity called by engineers resistance, and the three are related by the formula V = IR (I is for current, because C was taken.), or, equivalently, I = V/R and R = V/I (see this mnemonic). In other words, pushing harder through the same pipe means more water will move, and if you want to get more water through a narrower pipe, you have to push harder. This is called Ohm’s Law.
Continuing our analogy, we can see why too much voltage might be dangerous; high pressure water can do all sorts of things, from spraying all over the kitchen to cutting through steel. Therefore, our devices and power supplies must agree on the voltage. Current, however, is restrained by resistance; if your device demands 2 amps, but your power supply could supply 10, nothing will be harmed. The device simply doesn’t open the tap wide enough for all that extra current to flow out.
We know, for instance, that Norns Shield requires 5 (or so) Volts, and consumes at most 2 Amps, so by Ohm’s Law, we see that R = 5 Volts / 2 Amps = 2.5 Volts per Amp. “Volts per Amp” are known as “Ohms”, so to your USB power supply, Norns looks rather a lot like a 2.5 Ohm resistor. If you were to feed it 12 volts - that is, to push the “water” about two and a half times harder - it would want to flow I = 12 Volts / 2.5 Ohms = 4.8 Amps, which is really rather a lot more current. Even at this very basic level, you can see that doing this would probably be quite bad for it!
Of course, it isn’t quite the same as a basic resistor - for instance, it shuts off entirely if you give it less than about 4.8 volts, and would very likely break down immediately, make a loud popping sound, and stop conducting at all if you gave it 8 or 12 volts - but that’s the principle.
This should also tell you why it’s a bad idea to plug Eurorack levels into gear, like Norns Shield, that expects line levels. Eurorack can generate voltage differences of 10 Volts, while line levels are 1 Volt max and instrument levels are much, much lower. A clipping output on your Eurorack could be pushing 10x as much current through the sensitive analog to digital converters of your audio interfaces as it’s intended to handle. Most circuits will have overvoltage protections, but some may not, and anyway it’s a bad idea to rely on such safety features in everyday usage.
I hope this is helpful and not just a totally incomprehensible wall of text. If so, I would love to put together some basic-level posts on how resistance affects pitch stability, capacitance, and other useful things. And as I mentioned, please use this thread as a space for music- and art-related EE questions!