From Thomas Henry:

I've been designing electronic bass drums for some two dozen years now, but the Bass++ is by far the best, if I may be so immodest. It uses no hard-to-find parts, is very stable and predictable and is a snap to build, weighing in at two chips only. And since it employs legitimate analog synthesizer technology and not the old ringing filter routine, it is very quiet. Before continuing, let me hasten to add that the Bass++ is great for bass drums (of course), but also is perfect for tom-toms, woodblocks and related instruments thanks to its wide range.

From Timo Rozendal:

Changes from original design: 
- sensitivity pot is moved to back of module 
- provided panel pcb, so no wiring required 

explanation 
-impact is a clicky impulse 
-shell is a triangle-like tone 

The panel icons might need some explanation, or just some wiggling  , I will make an explaining picture later. 
but if these are the pots: 
1 2 
3 4 
5 6 
7 8 

then they are mapped to: 
1. impact level 
2. impact tone (left is muffled, right is bright) 
3. shell level 
4. shell decay length (mapped to amplitude) 
5. shell tone 
6. shell sweep (amount to which the decay influences the tone) 
7. shell cv (amount to which the cv input influences the tone) 
8. total level