Portable USB sound card with 48V phantom power and microphone preamp

The design goal
is to create a sound card primarily for microphone recording. Requirements include a small size, XLR input, and 48V phantom power.
The chosen
USB audio chip is the TI PCM2912A, released over a decade ago. While its performance is outdated and it's not cheap, it requires no firmware flashing, is ready to use immediately, and has detailed and easy-to-understand official documentation, making it suitable for beginners like myself. The XLR interface requires a differential-to-single-ended converter to input the PCM2912A, so the ADI SSM2019 preamplifier chip was chosen. It has adjustable gain but requires both positive and negative power supplies. The power supply is the only original component. The phantom power supply requires a DC 48V supply. The conventional approach is to boost the voltage and then filter it, or boost it to around 20V and then double and rectify it. However, considering the complexity of the power supply design and the positive and negative voltage requirements of the preamplifier chip, I used two Mornsun B0524S-1WR3 5V to 24V power modules in series. After filtering, the output is 48V. Simultaneously, the zero potential of the SSM2019 is separated from the circuit's GND and connected to the midpoint of two series-connected 15V Zener diodes to obtain a ±15V power supply. Based on my personal experience
in structural design
, for microphone circuits, proper shielding can significantly reduce background noise. Therefore, a metal casing with good electrical contact between components and connection to GND on the circuit board is essential. Initially, I considered using a 26mm diameter cylindrical aluminum tube casing for an 18650 power bank kit, but with several large capacitors and power modules in the circuit, the internal space was too limited. Therefore, a 32mm square aluminum tube casing was used. The anodized layer on the aluminum casing end cap is sanded off, and the PCB is connected via enameled wire. Holes in the end cap are made using a bench drill and file; alternatively, you could try designing the PCB to make the end cap, remembering to add copper plating and solder mask openings. For the PCB GND, you could try directly soldering a window at the contact point with the aluminum casing slot.
The XLR connector is obtained by cutting off part of the plastic from an XLR male connector
(I bought a refurbished chip; the silkscreen printing disappeared after wiping with alcohol...).
The circuit packaging is rather messy; 0603 resistors are used, along with 0805 and 1206 capacitors. The headphone section is drawn rather haphazardly; it can be modified if required.