Yamaha DTXpress/DTXplorer/DTXtreme

Thanks for the comment regarding my initial problem. I replaced the 
transistor with a new one with a higher current gain (580 versus the 
the old one with 290 hfe) and it did improve. But the sensitivity is 
still a tad low. I still need to hit the pad harder than normal to get 
the module to register a sound, and it will not pick up any rolls. The 
rest of the circuit is exactly like the diagram except R3 is omitted 
(open) and the diodes are 1n4148.
The DTXpress module I am using is the first version. I wonder if its 
trigger is slightly different than the later versions?