I 'have also done some experiments involving input to the MOSFET drivers - the UCC37321/2
chip enable pins are pulled HIGH (internally, according to the datasheet) so I was/am confused as to how to use them. Other people have used the enable pin to turn on the enable pins (providing a HIGH - 5v logic signal). Since the datasheet indicates that they are normally pulled HIGH I thought that possibly using a totem pole configuration (NPN and PNP transistors tied together) could keep the enable pin pulled LOW (off) when there was no HIGH (on) signal. I tested this and it did not seem to change performance except that the coupling between the primary and secondary coils increased and the current levels through the primary coil increased to the level that the wires heated up and melted the polypropylene insulation I had between the primary and secondary coils.
I have also built the audio modulation board from The Geek Group, with a few changes (which I will post soon). I decided to put this together myself after I found that The Geek Group no longer had kits in stocks. In addition, the schematics they put up are missing the actual interface between the interrupter board and the driver board for the primary coil (not that hard to figure out, but is missing - I will also post this when I'm able).
A little side note - I'm trying to collect materials to build a DRSSTC, which requires high voltage/high current capacitors for the primary coil. When I can find these I'll be able to build a coil of the same size that has a much greater output (more impressive display for the same size coil).