Yamaha DTXpress/DTXplorer/DTXtreme

--- 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.