giuliomoro Setup 1
Leave the L and R inputs disconnected
https://i.imgur.com/FqF9P73.png
Nothing, actually (ground is connected, pin L and pin R are both unused)
giuliomoro Setup 1
Connect the L and R inputs to ground.
https://i.imgur.com/C2jjq9t.png
Nothing, as expected.
Additionally, I've tested connecting the condenser mic, with the 3.3V circuit in L while the R input is unconnected
https://i.imgur.com/zLIZL0x.png
That is when I get the signal (the microphone is OFF, but connected to input L).
giuliomoro Setup 2
Power the speakers from your laptop
Same as below: the mic picks up the signal with the same amplitude, and nothing when it's turned off.
However, when boosting up the volume, you can clearly hear that loud humming that I recorded a few posts ago.
giuliomoro Setup 2
Power the speakers from a separate USB power supply
https://i.imgur.com/AVKuVrF.png
The input is properly picked up (mic is ~1m from the speaker, and it is about as loud as a phone ringtone), and also disappears when I turn the microphone off.
More importantly, the speakers don't have any loud humming.
So powering my speakers from an external wall-plug power supply seems to fix the speaker issue completely.
But there's still the issue with my mics.
I'm still unsure if my condenser microphones are powered properly, now that you've mentioned phantom power is meant to be ~15V minimum, and seeing that I'm only using 3.3V with a resistor with them -but I don't know enough to make that call.