Hi,
100kV and audio on the same board.
100kV is dangerous...and "audio" sounds like a consumer product. This is not a good combination.
Limited safety and random users.I don't like the idea.
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Each country has it's own safety regulations...i recommend to have them all by hand.
Usually there are recommendations on plastics in those papers.
I assume for that high voltage epoxy is a good choice.
You need a huge air gap and huge creepage distance.
Be careful.
Klaus