Hello. I am currently working on a DD-11 from Yamaha I picked up for cheap. It was in a bad condition and I decided to free its soul and make it more Kosmo compliant. Everything worked good or better than expected until i noticed that i don’t know how to replace the piezo pads with push buttons…
could one of you provide some knowledge? I found some moded YM-Drums online and I remember Sam tweaking one for the museum. I’m open for suggestions, preferably with ~detailed instructions… 
Are you sure you want to do that? The piezos provide more functionality, in that they tell not only when a pad is struck but how hard. As such they’d be handled in the electronics very differently from a switch. It wouldn’t be just a matter of substituting piezo with switch, you’d have to go into the schematics and figure out where the piezo signal is discriminated to provide a trigger and probably wire the switch in there, maybe with a gate-to-trigger circuit.
I did not think about “dynamics”. the push buttons offer poor UX anyway. There is also the midi functionality to drive it (dynamicly). I thought of the push buttons as preview. the original pads are so big. they would occupy additional 40cm of kosmo space.
this clearly requires more thinking 
Make smaller piezo pads! The only reason the pads are that big is to make them easy to hit with drum sticks. It you use a material that’s thinner or softer (not to soft, you don’t want to break the piezo ceramic) then they should also be more responsive.
You can use hot glue to attach the piezo disk to different materials to test them out (and for the final build) lots of cigar box guitar pickups are made this way.
I also think smaller piezo pads would be the way to go - my gut says start with materials that wouldn’t dampen the impact as much as the large rubber pads, as your fingers won’t have the same impact as a drum stick… but I imagine the dampening also helps to prevent accidental triggers. Will be interesting to see how your material choice affects everything!
I heared you! I’ll use the original pads for now. i was not sure if i could separate piezo and pad eight times without causing damage. the original pads also have dampening spacers to prevent resonances in the case from hitting them. I’ll keep them separated and modular
I’ll take a beauty shot once it is completly wired up and working.
Done. I left the push buttons in there but they are not hooked up. I’ll add an additional power adaptor to run it on synth power from the inside of the case.
I have an other patient on the table. a DD-12 this time.
Seeing this I think circuit bending and the first thing for me to do would be to find the pitch point to add a pot.
It looks like there is no crystal, so it’s probably a resistor somewhere that’s doing the job.
like here
With speed research, it’ seems there’s a crystal somewhere and you need to use a LTC1799 for the pitch mod.
There is progress but I am not done yet… I’ll post new pictures once it is done. I have to build a new case for it. I could not justify chopping up the rails of one of my existing cases to make room or a double height module… I’ll need an additional case sooner or later anyway
