The first 2 circuits are totally unsuitable for audio (or anything else for that matter) and leave out many parts you should leave in.
The circuit in the third link is much better, but a couple of points must be made. PCB layout and or perfboard wiring is critical to get any Voltage regulator circuit to work correctly.
1. Do not use the PCB layout in the third reference. The layout allows probably 10 times (20dB) more ripple than necessary because of the way the ground trace is arranged. For low-ripple operation, the layout MUST have direct, FAT TRACE connections as follows: Transformer to Bridge Rectifier Diodes. Rectifier Diodes to Positive and Negative terminals of main Filter Cap (1000 uF in link #3). The Input terminal of the 317 should connect to the Positive terminal of the main filter cap thru a separate trace, and the Regulator Output ground connects to the Negative terminal of the filter cap with a separate trace. The transformer/rectifiers charge up the main filter cap in short VERY high current pulses that will cause voltage drops in the PCB traces no matter how fat they are, so you give this pulsing circuit its own path from transformer thru the rectifiers thru the CAP and then back to the transformer. The regulator circuit ground STARTS at the negative terminal of the main filter cap and goes to the output terminal of the regulator. All the regulator grounded references (The lower voltage set resistor and the reference filter cap must be attached to the output terminal, or even better the negative pin of the output filter cap (470uF in ref 3) by a separate trace so that the ripple flowing in the high current filter cap charging loop doesn't infect the regulator output with ripple.
2. All these regulators show a 220 Ohm or 240 Ohm reference resistor. This resistor loads the regulator output with 5 mA. The LM317 requires 10 mA minimum load. To make sure the regulator operates with no external load applied or very light loads, use 121 Ohms here and approximately 2.2K total resistance between the output common and the LM317 adjustment terminal for 24 Volt output. The bottom (2.2K) resistor should connect directly to the negative terminal of the 470uF output cap thru its own trace -- not a big fat ground trace. The 121 Ohm resistor should be wired between the output and adjustment terminal of the 317 by the shortest, most direct connection possible. All the protection diodes must be there but their connection locations are not critical since they only work in case of "emergency". There is no bleeder resistors shown in any of the schematics to discharge the supply caps when unloaded. A 4.7k 1.2 watt resistor across the output terminal will draw 5 mA and discharge the supply caps when the supply turns off and is not connected to the audio circuitry. With the resistor in place, one can then use the 220/240 Ohm reference resistor because the 4.7k bleeder resistor provides the other 5 mA of required load.
3. Use 100 uF instead of 10 uF for the adjustment filter. Its negaive terminal should also attach to the output cap ground by its own trace (or it can be wired in parallel with the low side of the 2.2K adjustment resistance.
4. When applying the zener clamp for a 48V supply, connect a 5 Watt, 56V zener with the cathode (banded) end pointing towards the regulator input and the anode end connected to the regulator output. Do not leave out D2. The zener is wired in parallel with it. The protection diodes should be 1N400x types.
5. All the circuits referenced show the lower resistor as a wide ranging pot (1.2Volts to 30 Volts). If you know you want 24 volts then you need about 2.2K total. So use a 2K resistor in series with a 500 Ohm pot wired as a rheostat -- connect 1 end to the wiper. This gives you a much smaller adjustment range that will allow you to easily dial in the exact 24 volts. The total resistance is 2.0k with the pot rotated to minimum so the wiper shorts out the pot and 2.5k with the pot rotated to max voltage with all 500 Ohms of the pot in series with the fixed resistor. Never use the wiper of the pot as a direct output, as shown in ref 1. Always connect it to one end, to limit the maximum resistance due to an open wiper or even a scratchy pot. The connection in the first reference is dangerous as an open on the wiper will allow the regulator to go all the way up to the unregulated voltage.
6. PCB, perfboard layout or even point to point wiring of the power supply is critical to good performance of any 3-terminal regulator. A bad layout can cause the regulator to output volts of ripple. I have reworked Power supply PCB's on commercially built supplies that had layout errors that caused excessive ripple. KT DN780 and SW Series 20 original supply are two that come immediately to mind. A simple 3-terminal regulator circuit may not seem hard, but there is more to it than meets the eye. Just connecting up everything according to a schematic will seldom give the performance you want. Unless you really want this as a learning experience, consider purchasing a linear supply made by International Power or Condor or Power-One. Their PCB layouts are correct, their transformers are properly sized, and they are relatively cheap.