Magician:
I'd suggest darlingtons array, ULN2003A or may be ULN2001A with base R barely enough to trigger with higher voltage and not with lower. Other option is optocoupler, with couple resistors in front as voltage divider.
Funny to me neither of those 'solutions' seem useful or possible to differentiate between two signals, one at 1vac and the other at 1.5vac? I don't think those ICs or any led based opto could be turned on with such low voltage levels?