This project came about because of the new EU recommendations to have energy-efficient "wall wart" supplies. These are typically SMPS and thus only have DC output, so there is a need to obtain a split supply for powering high-quality op-amp circuits. The board features the option to fit a LED to give indication when power is on. The input is filtered to make sure any residual noise from the SMPS is kept out of the audio. The input also features reverse polarity protection.
The diode at the input prevents current flow in the wrong direction so acts as a reverse polarity protection. The LED will light whenever the circuit is connected to the powered wall wart. The resistor and capacitor form a low-pass filter which drastically reduces any remaining noise on the output of the wall wart. The resistor and diode string bias the transistors at a few mA to provide a good clean low impedance ground. The transistors don't really get hot and the emitter resistors provide feedback so there is no thermal runaway problem. The capacitors on the output just add that little extra smoothing and impedance reduction.
Printed Circuit Board
PDF of copper side of PCB
PDF of component side of PCB
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