Yamaha DTXpress/DTXplorer/DTXtreme

Keith,
Wow, thanks for the great info! I'll try to incorporate your 
suggestions, and of course, I'd be happy to see any circuit 
corrections.

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. The way I have it setup I expect A and B 
(and D) to actually not be hit at the same time. Turns out trigger B 
and D are a almost too sensitive. With the single piezo mounted on 
the shell, I can hit anywhere on the rim and the piezo would 
trigger, but sometimes whacking on the mesh would shake the shell 
enough to trigger it also (esp. on rack mount), so I've added a gain 
reduction pot on the rim piezo and it eliminated the cross talk 
problem with the mesh. The one thing is, the dynamic range of the 
rim hit is a little narrow, which I think is due to a combination of 
how it is incorporated on the shell the velocity needed to cause the 
switch to trigger, and possibly the circuit. The main trigger seems 
to maintain the full dynamic range without any problems.

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

Thanks again for your help.
- Rudy

--- In DTXpress@yahoogroups.com, "Keith" <keith@k...> wrote:
> 
> --- In DTXpress@yahoogroups.com, "captainbingo" 
<captainbingo@s...> wrote:
> > 
> > Ed,
> > Thanks. Yes, without knowing his circuit I'm sure Keith1200rs' 
magic 
> > box is MUCH more sophisticated than what I came up with, and I 
> > completely understand Keith1200rs keeping his under wraps. As a 
die-
> > hard DIYer, I wanted to make the most use out of my DTX module, 
> > which is outstanding (despite the rather cumbersome user 
interface), 
> > but I suspect my circuit has "bad grammar" and needs 
> > the "punctuation" fixed. :)
> > 
> 
> Sorry for the delay - I have been out of circulation for the last 
few
> days.  I spend all week on my computer so often at the weekends I
> don't even turn it on so I get a break!
> 
> If you want to email me I am happy to help where I can.  
> 
> Looking at your trigger circuit, I would suggest increasing the
> operating voltage to 24V from your current 9V.  As you have found, 
the
> piezos can give out a fair voltage.  I have tended to use 100k as 
the
> input resistance, rather than 1M, capacitively coupled it to an
> internally generated +12V point (the circuitry is running on 
+24V). 
> This is really just to give me the headroom I need to handle big
> signals.  The problem with your circuit is that it is referenced to
> ground so you will be chopping off the negative going part of the
> piezo signal (and giving your LM324 a hard time with the negative
> spikes - they may well blow up).
> 
> To add two signals together, you cannot just connect the outputs of
> two opamps together (not with predicatable results). Take a 
resistor
> from each opamp output to a summing node - 1k to 10k from each 
would
> do.  I would imagine your rim trigger from input B is not very
> sensitive.  If you like I can send you a better circuit.  On the 
4066,
> you will need a pull down resistor on pins 5 & 13.
> 
> Ed/OGD - I need to decide soon what to do about the "magic box".  
My
> current feeling from the feedback I have had is that while it 
works,
> setup is tricky.  I seem to be able to get it set up better than
> anyone else, but then I understand exactly what the circuitry is
> doing.  My feeling is that it will be difficult to turn it into a
> simple commercial product.  More adjustments will just make it 
harder
> to set up.  If you think that is a fair assessment, I will post the
> circuits here so anyone can play around who has the inclination.  I
> will make my fortuen elsewhere ;-)
> 
> Keith.