RA-33 Header Explanation

Headers H1 and H2 are the interface for installation of optional audio amplifiers or filters.  
While this header can be used for multiple functions, its main purpose is for easy interfacing 
of the FL-10 filter board.  When the FL-10 is not installed, a simple 2-pin header jumper is 
fitted onto the center two pins of the header completing the audio path. 

To use the optional FL-10 filters, simply remove the 2-pin jumper and 
install the option observing polarity.  The ground connection is nearest the silkscreen 
markings "H1" and "H2". Consider using higher than 5V for the filter operation by selecting
the "B" position on JU2 and feeding 10 to 16VDC into pin 9 of the DB9.