Originally Posted by H.M
BTW : About the piezzo mod -> Nice. I think that the modification can be less difficult with a mosfet. have you tried this?
An update on this: A MOSFET on its own doesn't work because the Step pulse is so narrow. A MOSFET followed by a lowly BC547 works a treat, however - the long storage time of the latter widens the Step pulse nicely. An updated schematic will follow.