These are smaller electronic projects which I have built over the years, and I don't deem worthy of a full article.
This was a project to make a high performance USB audio DAC and headphone amplifier without resorting to full "audiophoolery". It is designed as a two board system. The first board processes the digital audio and contains switching regulators to generate a bipolar ±10V supply from the USB 5V. The second board is the analogue board; containing the DAC itself and the headphone amplifier as well as linear regulators reducing the analogue supply to ±8V to minimise noise.
The USB interface is handled using TI PCM2705, which provides an S/PDIF output (the analogue output from this chip is not used as it's performance was deemed too poor, particularly in terms of SNR). The S/PDIF signal is converted to I²S for the DAC using a Cirrus Logic WM8805. An auxilliary S/PDIF input is also provided; allowing use with an S/PDIF source and at bit depths/sample rates higher than 16/48kHz. As well as the voltage regulators, the digital board also has an ATmega328P microcontroller for system control purposes. Its main task is to monitor the volume and input buttons; and update the DAC/WM8805 settings as needed over I²C. The audio board uses a PCM1792A DAC; OPA4134 op amp for I/V conversion; and TPA6120A2 amplifier as the final headphone amplifier.
The end result has performed very well for a few years. I have never noticed any background noise, unlike many integrated and cheaper sound cards. It has been used with both low-impedance and high-impedance headphones; and has even been used to drive 8Ω speakers at a low but acceptable volume.
This was intended primarily for a high altitude balloon project where we were likely to need to track multiple balloons and also ideally wanted backup receivers in case a computer crashed. We were using LoRa radios at both 434MHz and 869MHz, so I designed the board so it could be built for both frequencies. It consists of a TDK SAW filter (B3710 or B3725) for improved out-of-band noise rejection, particularly useful in the 869MHz band; a Macom MAAL-010704 LNA and an inductive splitter going to the 4 output SMA connectors. There is also an onboard 3V LDO allowing it to be powered from a 5V supply.
Unfortunately I don't have the equipment to test a device like this properly, however a quick test using background noise and an RTLSDR dongle suggested it was working well. Actual performance in use has also been very good.
Design Files (KiCad + Gerbers) on GitHub