Today I got the answer from Conrad.se about the Piezo that I thought could be used. They say:
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The piezo of your drumkit cannot be replaced by the article 710397. The impedance of the article 710397 is only 200 Ohm.
We would gladly have helped you, but unfortunately, we have no
items with the specified technical characteristics in our delivery programm.
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I have to check elsewhere then... Story continues...
Actually, I wouldn't worry about their comment a bit... If you notice the piezo I gave you a link to is 500 Ohm .... I've been using those for years, and many other 27MM, 20MM, 35Mm piezos with Roland modules, Alesis modules, and 2Box now ...
Piezos are normally used with voltage to them to cause the piezo to bend and vibrate creating a buzzer, or a sound ... We are not using them that way, they are more like a Vibration pickup with tiny voltage changes sent ... so those stats won't be so important ... The piezos you were looking at look like they have a separate exciter area on them ... it is the extra little cutout area at the bottom of the piezo ceramic ... you don't need that ... but even that is not a problem really, you just don't use the wires from that little section .. So, what I am saying is ... I pretty much would guarantee those would work ... but if you can get a normal 27MM piezo more like the one I gave you a link to without the exciter cirquit that would be better IMO ... Or heck, just contact 2Box and see if you can get piezos from them ... they may be willing to help you out .... J