Audio probes are great for troubleshooting. A cheap, quick, and effective one can be made very easily out of an oldy-worldy crystal earpiece, like your grandparents / great grandparents might have listened to their cats-whisker radio on.
They’re still readily available on Ebay, etc.
All you need to do is cut off the 3.5mm jack or whatever, heatwrap and solder a thin gauge wire to one end (the “probe”) and attach a crocodile clip or whatever to the other.
That’s it – you’re done. Attach the croc clip to your circuit’s ground, and touch the probe to IC pins or components in the audio path to test.
Don’t put it directly in your ear, though, unless you really don’t value your hearing and fancy a good headache.
