Yamaha DTXpress/DTXplorer/DTXtreme

Hi all,

Many of you will have seen discussions about the "Magic Box" which
will allow two pads to use one input on the DTXpress, and also combine
two piezos from a single pad into a single piezo and rim switch signal
for use on the DTXpress (some non Yamaha dual zone pads use two piezos
instead of a single piezo and a rim switch).

I have designed a circuit which does a reasonably good job of doing
this and a few people have tried it out.  It is not 100% perfect and I
am not sure it ever will be - it has to work within what the DTXpress
expects from a pad with rim switch - but it is pretty good.  However,
I am not sure it will be viable as a commercial product and am not
prepared to spend a lot of my own money to find out.

As the original "Magic Box" was quite complex, I have come up with a
simplified idea which should be within the abilities of anyone who
wants to have a go.  The components will only cost a few cents and the
circuit is "passive" in that it does not use any external power (but
has an "active" component).  I have given it a quick try and it works
and should be good for a typical use where you want to add a few pads
for cow bells, extra cymbals etc.  Bear in mind that when combining
two pads into one input you can only get one sound at a time (although
you can get both if one hit is slightly after the other) so you need
to choose your combinations with some thought (ie don't combine the
kick drum, snare or high-hat with anything).

With a few extra components you could also combine three pads into
one.  I have posted a circuit to the files section.  It is supplied
without any warranty, but as it has now power, it is difficult to see
how it can damage anything.  I have not optimised the component values
- I haven't time at the moment - so you may want to play around with them.

I will try to answer any questions posted to the group as quickly as
possible.  If anyone wants the more complex circuit, please ask.  It
has opamps, comparators, inductors, power supply etc and would need a
stripboard or something similar to build it on.  The parts to build
one would probably cost around $100 (I am not sure of USA component
prices) and it would combine 8 channels into 4.

Keith.