Then new Karp / DU-KRPLS core circuit provides a better, louder outputs. We'll provide free assembled core PCB to owners, please email me with your proof of purchase (emails that did the purchase, or a picture with your email on a paper with your module, etc), shipping will be 10$ airmail. Or purchase from shop and let me know in the comments.
Below is the method of replacing core board.
1) separate the core PCB from the module
2) carefully take out the MCU with pliers
3) take out the opamp with pliers
4) plug those 2 chips on the new core board
5) mcu needs some pressure
6) the U gaps on chips needs to align with the U gaps on pcb and IC sockets
7) plug the new core board to the module, and enjoy.