Yamaha DTXpress/DTXplorer/DTXtreme

> BTW, I'm actually not trying sum the outputs from A and B. I'm 
> trying to use the op amp as a buffer/voltage follower to keep input 
> A from triggering input B.

But the circuit you have connects the output of IC1A, IC1B and IC1D
together.  Given they can each sink/source around 50mA, you will have
a battle on your hands when they all try to do something different.

> Also I have noticed that the polarity of the pizeo can made a big 
> difference, probably due to the ground reference you mentioned. 

From my experience they tend to respond to the positive going pulse. 
If the piezo is the wrong way round you will miss that and only catch
the next half cycle of the waveform which can be considerably smaller
depending on the pad (I am thinking of the Yamaha pads here).  I
assume you don't have an oscilloscope to see what is going on?

> And 
> I found it odd that on the 4066, for the D input, the resistance 
> wasn't 10K, but something less was need to make it work. I had 
> assumed that the 4066 added it's own internal resistance...hmm.
> 

The resistance should be zero for rim switch one and 10k for rim
switch two.  The 4066 resistance should only be a few hundred ohms at
most, so I am surprised you need to drop your series resistor so much.
 Are you sure you want it to be rim switch two, and not rim switch one?


Keith.