Giovanni,
Sorry for the late response.
In reference the “quick start guide”…First of all make sure the depth, attack, and release knobs is all the way to the left. Plug in headphones or computer speakers and then test it again. If you still can’t hear any sound, then double check your solder joints in the audio section of the circuit board…which is all the components connected to the LM396 amplifier chip. Make sure everything is connected properly and nothing is connected that shouldn’t be.
If you still can’t figure it out, let me know and we’ll start looking at the voltages around the audio section to see if everything is functioning properly.
Good luck.
-Brach