Karp / DU-KRPLS new core PCB
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.