When I see this question, I suspect that you're trying to use 48VDC phantom power, from a mixer or something like that, to power an electret. I've done that, and it worked quite well. If that's what you're trying to do, or something like it, say so, and I'll try to remember how the gizmo worked.
Yes you can use a regulator to regulate that down to 9V. Just use a big heatsink. I'd suggesting using a LM317HVT <--- note: HV type
Phantom powering is not always implemented correctly or adequately, even in professional-quality preamps, mixers, and recorders. In part this is because first-generation (late-1960s through mid-1970s) 48-volt phantom-powered condenser microphones had simple circuitry and required only small amounts of operating current (typically less than 1 mA per microphone), so the phantom supply circuits typically built into recorders, mixers, and preamps of that time were designed on the assumption that this current would be adequate. The original DIN 45596 phantom-power specification called for a maximum of 2 mA. This practice has carried forward to the present; many 48-volt phantom power supply circuits, especially in low-cost and portable equipment, simply cannot supply more than 1 or 2 mA total without breaking down. Some circuits also have significant additional resistance in series with the standard pair of supply resistors for each microphone input; this may not affect low-current microphones much, but it can disable microphones that need more current.
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?
QuoteIs 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).