Ok, but aren't you using some sort of AC power supply anyway to make the 12V to run the low-level circuits?
If you are working with audio, the last thing you want is to use the same 12VDC supply to power your audio circuits as will power the step-up converter. The converter input current is a square-wave which will be very hard to prevent from injecting noise into any other circuit that is powered from the same 12V.
As I said earlier, that step-up converter is a very primitive (naive) design. A proper step-up converter circuit is much more complicated, and uses some specialized components (inductor, catch diode, FETs, special IC) than a simple transformer, diode-bridge, filter capacitor, bleeder resistor analog brute-force power supply. The transformer based supply is much easier to build, especially for a novice.
The hardest thing about building the transformer based supply is obtaining the transformer. If I knew where in the world you were, I could suggest some sources for the transformer, including knowing the primary voltage (120V or 240V)?