DVDdoug:
Is it possible that the sound card phantom power isn't able to sink enough current to make work properly the 7809 or LM317HVT converters?
The regulator itself (with no load) doesn't require any significant current. You need to be concerned with the voltage into the regulator, the voltage dropped across the regulator, and the current through the regulator to the load.
And, I would guess that the current required for an electret microphone is no problem either. If you start "pulling" significant current, the regulator can overheat since you are dropping 30V across it. (Heat = Power = Volts x Amps). If you don't know the current required, and if you can't measure it, you'll just have to try it. If the regulator gets too hot to touch, you need a heatsink or some other solution.
I agree with Mark, and I'd stay-away from switching regulators in a microphone preamp circuit (where you want the lowest possible noise).
Well in context of what the OP wants to do (use the 7809 with phantom input power) the statement "The regulator itself (with no load) doesn't require any significant current." is incorrect. A 7809 datasheet I looked at says the Quiescent Current of the regulator is 6ma. Phantom power is limited to one or two ma so there is no way you can use that regulator using phantom power for its input source.
Lefty