Get an isolation transformer and a cheap storage oscilloscope.
A good oscilloscope is stupid expensive but is also amazing for this type of work. I count myself lucky I have a friend who's an electrical engineer and I can borrow his work one. It makes everything so much easier.
I'm sure for someone experienced the benefit is marginal but having a bunch of probes and being able to see the waveform feels like cheating for an amateur like me.
Get old stuff. It's possible to acquire old oscilloscopes and all sorts of (once really expensive) lab equipment for free or for cheap from trash bins at universities or from the Craigslist equivalent in your country.
> A good oscilloscope is stupid expensive
They're not that bad. You can get a good entry-level oscilloscope from a company like Rigol or Siglent for ~$300.
You can get an extremely shitty one for 20 dollars https://www.instructables.com/Flea-Scope-18-Msps-13-BoM-WebU... but when you are just starting its pretty cool!
The cheapies are less useful for debugging real problems, due to their bad UI and severe limitations.
A good, fast reacting multimeter is likely better thing to get than a cheap scope.
That said the cheapies might be usable for debugging audio stuff.
I think that's probably true, but for learning stuff I think an oscilloscope is way better than a multi-meter and the cost is prohibitive so I love the flea scope to give to noobs.
I am also very much in the belief system that you should not buy an expensive tool before you are frustrated with a cheap one, most of the time people get into random hobbies and bow out six months later with way too much crap on their hands, and often time tools are more for show than for real world use.