Yamaha DTXpress/DTXplorer/DTXtreme

Hey Keith,

>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.

I have it setup based on a few circuits/documents on the web that 
talked about using an op amp as an impedance buffer, allowing the 
input to be "isolated" from the output. Before I added the op amp 
buffer, banging on A would trigger B. If I hit A/B/D simultaneously, 
B always wins. But you are correct, it would be much better to 
properly isolate each trigger.

>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?

I agree, I always thought the postive => pulse, but I found it odd 
that the TP120SD has the black wire (the one going to the brass 
plate on the piezo) going to the tip on the plug. I also noticed 
that when I switched my piezos on my toms to have the black go to 
the tip (ignoring the DTB, going straight to the module), the gain 
was much higher. I thought that was interesting.

Yes, I wish I had an oscilloscope (hmmm, I've always wanted one, got 
to figure out how to hide that from the wife, heh).

>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?

Yes, this was strange. I settled on the low resistance based on 
empirical testing. When I had it set to 10K, input D would "choke" 
out, like the switch was staying "latched" too long. I put a pot on 
it and played with the resistance until it triggered reliably, at it 
was at 5K. I just checked to make sure: Input B triggers R1 and 
Input D triggers R2.

Thanks again for your help! - Rudy