What's your soldering success rate?
Soldering mistakes are by far the most common thing to go wrong in do-it-yourself electronics. It seems like I spend most of my tech-support time gently urging customers with failed kit builds to re-check their soldering, and when I have problems in my own builds, those also usually turn out to be soldering-related. Everybody, myself included, tends to think of failed components as a likely cause of problems, and we spend a lot of time doing differential diagnosis to figure out which components might have failed; but then once the problem is narrowed down to a single component, the actual issue usually turns out to be a bad solder joint on that component, not the component itself. The real point of the debugging is often just to figure out which solder joints to look at more closely. READ MORE
More about DC coupling
Operational amplifiers ("op amps") are popular analog building blocks, especially in synthesizer electronics, because it's easy to analyse what they do to voltages. The first rule of op amp analysis is that (in negative feedback configurations, and when this is possible) the amplifier moves its output voltage in order to make its input voltages equal. That is useful in building circuits to manipulate DC voltages. READ MORE