A. A dual piezo interface for the Yamaha DTXpress I, II and III modules. It has also
been used with DTXtreme and DTX900 mdoules and Roland modules
Q. What does it do?
A. It uses the facility for dual zone triggering on the DTXpress and other modules
such as the DTX900, DTXtreme and Roland. This allows multiple sounds by using a “rim
switch” which is connected to the ring of the jack connector. The module detects
this switch closure and allows you to have a different sound for the rim. It only
uses one piezo. The DKDI-21 takes two piezo signals and produces one signal plus
“rim switch” type signal so you can have two sounds for each input. Normally only
a few of the pads on a DTXpress are dual zone, but the module supports dual zone
on inputs 1-8 (not DTXpress IV).
Q. Why would I want one?
A. When you have used all the inputs on the DTXpress and want some more. It is particularly
handy for adding a cowbell, chimes and other percussive effects.
Q. What about a 3 zone expander?
A. While a 3 zone expander can easily be made, the current version has been made
as a dual zone. As only inputs 2, 6 and 7 on the DTXpress III are compatible with
3 zone pads, its use would be more limited. However, if you want to build your own,
there is a schematic here DKDI-31.pdf
Q. What’s the DTXpander?
A. Originally there was a requirement for a “magic box” to make use of the unused
capacity of the Yamaha DTXpress modules. This became known as the DTXpander. As
this is in no way connected to Yamaha themselves, it is now called the DKDI-21.
Q. What are its limitations?
A. As it uses the dual zone facility of the DTXpress module, it has the same limitations.
In the same way that you can have either a snare hit or a cross stick hit on the
snare but not both simultaneously, the same applies to using the DKDI-21.
Q. Any other snags?
A. The DTXpress modules are not as sensitive to the rim hits as the main pad. This
limits the ability to use the “rim” pad for something requiring a wide dynamic range.
Q. Are there any adjustments?
A. There is a jumper to bypass a diode in series with the main pad piezo - experimentation
will determine which is the best position for the jumper. There is also a sensitivity
adjustment, accessible with a screwdriver through a hole in the case lid. The latest
circuit also has a jumper to disconnect D2. This would not normally be disconnected
on the DTXpress series, but some DIY pads and Roland modules may use it.
Q. What power does it require?
A. It requires no power. The piezo voltage is sufficient to turn on the switch transistor
in the expander.
Q. Does it work with other modules?
A. All development has been done with the DTXpress III, but it has been used with
several modules from Roland as well (e.g. TD6, TD7, TD8) and also the DTXtreme, DTXplorer
and DTX900 from Yamaha.
Q. What pads does it work with?
A. It has mainly been tested with Yamaha pads, but also used with Roland, Pintech
and home made DIY pads.
Q. Does it have any other uses?
A. It has been used for DIY Edrums. Building a dual zone pad with a piezo and rim
switch is tricky. Using two piezos is relatively straight forward. However, to
use two piezos would take up two inputs on the module and also risk crosstalk problems. Using
the DKDI-21 you can get a dual zone pad with two piezos using just one input on the
module. The same idea will also work with proprietary dual piezo pads, e.g. those
Q. What about the DTXpress IV?
A. The DTXpress IV does not have the excess of unused dual zone inputs that the DTXpress
I, II and III have, so it is unlikely to find much use with he DTXpress IV.
Q. How does it work?
A. It simply combines the two piezo signals. If it detects a signal on one of the
two piezo inputs it turns on a transistor connected to the jack ring.
Q. Can I build my own?
A. Absolutely. As of May 2016 I will no longer be making them. The schematics have
been made available on a couple of sites for home construction on the understanding
that it is for “personal use” and non-commercial purposes only. The circuit is here
DKDI-21.pdf (pdf file)