Review on 🔊 Enhance Audio Quality with KOOBOOK 2Pcs SSM2167 Microphone Preamplifier Board Preamp COMP Compression Module DC 3V-5V by Reggie Higdem

Product is practically useless without a diagram or link to it! If I missed it please let me know where to find it, thanks! With MSEE in hand, I figured I knew how to hook it up and test it, which I did. The data says the operating voltage is 3-5VDC, so I used a 3.7V battery and checked that the board was powered on. I connected the input and routed the signal back to the second input of the amp, so far so good. If you then examine the output, the result is: NOTHING. Everything else looks fine, correct component values and so on. No result found! I bought 4 of these while testing 3 and NONE of them work, although I've used different approaches I would write this before testing the 4th. I don't know what the problem is, anyone?