Obviously I don't know, what I don't know. Where do I go from here? I know that I need to deepen my understanding of the basic things I already know but I'm easily not finding the resources online to learn?
Khan Academy Electrical Engineering program
https://www.khanacademy.org/science/electrical-engineeringDigilent Real Analog class
https://learn.digilentinc.com/classroom/realanalog/There are literally thousands of tutorial sites on Google. You need to refine your search and look for specific topics.
You will need some math. Maybe you already have plenty but, if not, Khan Academy is a good place to start.
My goal is to someday be able to design and implement an analog synthesizer on my own. I've been looking at schematics for VCOs, VCAs, ADSRs, and so on, but unfortunately they all go right over my head. Like I could probably breadboard some of them and get them to work, but I wouldn't know why they were working, and if they schematic had an error, I wouldn't know. I couldn't adapt a schematic that works on +15v -15v to work on +12v -12V instead.
Due to op amp design, it might very well be impossible to make it work. The signal may have a high enough voltage swing to drive the +-12V op amp to saturation whereas the +-15V design had enough headroom. This is a datasheet issue!
You will also want to convert dual rail designs (like +-15V) to single rail (+5V?) designs. The book I recommended above can help with that. It should be obvious that signal swings will be more limited.
Rail-to-rail op amps try to minimize the issue of not being able to swing the input or output signals close to the rails. But read the datasheet! Some can go to the + rail but not the - rail, some are rail-to-rail on input but not output, and so on.
What is my next step? Are the resources available online or do I have to sign up for EE classes at a real school?
Advice is much appreciated.
Buy some op amps and play with them on a breadboard. I would suggest starting with +-15V amps (see videos for op amp selection) and moving to single supply op amps later on.
The LM358 is as good as any. Note that it can only get to about 1.5V from the + rail but apparently it can get all the way to the - rail.
This clipping phenomenon is described in w2aew's videos. He shows it on a scope.
Got a scope? Got a dual output supply? Signal generator? If you really want to do this thing and you don't have enough equipment, please consider the Digilent Analog Discovery 2 and the associated parts kit. It will allow you to track the Real Analog course. The AD2 has a dual output supply (low voltage, +-5V), dual channel oscilloscope, dual channel signal generator, 16 bit digital IO and logic analyzer. None of which begins to show you the tools in the Waveforms software. You want to see how an RC low pass filter REALLY works? Fine, use the Network tool. It will give you attenuation and phase shift versus frequency in a beautiful Bode' Plot.
If I were just starting out and wanted to LEARN electronics, the AD2 would be my first tool. It is truly a lab in a backpack (with a laptop) and totally capable of replacing a bunch of test gear. Read the instructions carefully, there are voltage limitations. Don't even think about using it on some kind of high voltage switching power supply.
https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/I bought the Jameco 20626 Dual Output Supply the other day. I haven't assembled it yet but I'll get around to it sooner or later. I had planned to use it as +-15V for an analog computer I built some time back.
https://www.jameco.com and search for 20626 The link is too ugly to post.