Q4 is Japanese NPN C1815.
K2 is DIP-2 Switch to select the right tone
If you follow http://pcb4diyeffects.blog.com you probably know what is this about. :)
SUBM BASS PREAMP
- added FET buffer. Optional to build buffered or non buffered version.
This creature will "smootherns and sweeterns the tone to give a fat and clear bass tone. It give fair amount of gain to your line level input"....you know what is this if you are a keen bass player. :)