Yamaha DTXpress/DTXplorer/DTXtreme

--- In DTXpress@yahoogroups.com, "Chris Todesco" <desco911@y...> wrote:
> Keith, PFozz, plhalli, et al:
> 
> My dad, who is much more of an electronics guy than I, first shorted
out the diode on the main pad (D2, essentially removing it from the
circuit) which cured the sensitivity problem on the main pad.  I might
have had the polarity flipped, so the first spike was negative, but
removing the diode seemed to bring sensitivity back to normal without
adversely effecting the rest of the circuit.  I understand the idea
behind this diode (half-wave rectifying), but it's apparently useless,
at least for Roland boxes...  Any idea what the deal is?

I don't know what Rolands expect - only the Yamaha.  I know all the
Yamaha pads I looked at have a positive going pulse first, and that
one is often considerably larger than the negative going half cycle
which is later, so polarity is important.  D2 doesn't do a lot - just
provide some symmetry between the two halves, so no harm in removing
it.  It shouldn't be detrimental if the polarity is correct, unless
the Roland pads are a bit feeble in their output signal where the
volts drop could matter.  D1 is essential otherwise the rim trigger
will trigger from either pad.

> 
> To cure the high threshold on the switch, I adjusted the resistance
of R1 down.  I brought it all the way down to 1.5k, and now it works
GREAT for all hits that can be heard, and I cannot get it to
false-trigger the switch on the main pad.  

Depending on the transistor you have used, you may blow it up with
excess base current with 1.5k - you can get > 20V out of the Yamaha
pads.  Still, transistors are cheap.

> It DOES get confused for VERY light hits, but they're so light that
I can't even hear the sound, and the only way I can tell it's messing
up is to go into the trigger editing screen, where I can see what's
being triggered.  

This will always be a issue, even with more sophisticated circuits.

When I build your circuits for use on my kit (instead of on
breadboards), I'm going to put pots in there so I can adjust the
thresholds.  So, plhalli, since you're having this issue too, try
lowering R1's resistance.

I am pleased someone is finally getting a chance to use the simple
circuit.  When I get chance I will do some more work on it.  I think
that somewhere between the rather simple circuit I have posted, and
the complicated one I have also built, there is probably a good
compromise, with better performance than the simple one but not as
complex and expensive as my other one.

Keith.