Since this is a development board, raising the sound might be something that requires extra knowledge. Because of that, I recommend checking the website listed on Google Search. You have the possibility to download the PDF files with information about the Clino Phon 99.
Google Search: http://goo.gl/60UKyn
I have recommended this way, because no other user encountered the problem, which means it's a local issue that can be fixed with the help of the information found on the PDF files.