The circuit is “almost” a simple op-amp current-to-voltage (transimpedance ... adds some diodes in the feedback loop to reduce the output range. Since the output is going into a ...

but suffers from an output impedance too high to drive a set of headphones. An NE5532 steps in for the op-amp buffer role, making for a very simple circuit. Power comes from a set of four 18650 ...

Rather than having an external boost converter to produce enough volts, this design adds just two mosfets and an inductor to the Class-D output structure (see diagram ... and TU Delft presented a ...