“This is a headphone amplifier project for audio digital-to-analog converters (DACs) with differential voltage outputs. This circuit converts the differential voltage output of the DAC to a single-ended, ground-referenced signal and provides the additional current necessary for low-impedance headphones. Project is built using OPA1688 low distortion, high-drive Sound Plus audio amplifier. The circuit tested with dual +/-5V DC supply, and it can drive a load 16 Ohms to 600 Ohms. Headphone amplifier provides an output 50mW into 32 Ohms. Signal for the right channel and left channel input is applied to the amplifier through connectors CN1and CN3, respectively.
The positive input from the source connects to the pin labelled I1+/I2+, the negative input from the source connects to the pin labelled I1-/I2-, and the ground connection from the source connects to the center pin of CN1 and CN3, labelled GND. Stereo 3.5mm Female EP socket provided to interface the Headphone. The project supports headphone of 16 Ohms, 32 Ohms and 600 Ohms, output power of the circuit depends on impedance of headphone, for example, a pair of headphones with a 95dB/mW sensitivity given a 3mW input signal produces a 100dB SPL. If the headphones have a nominal impedance of 32 Ω, then the voltage and current from the headphone amplifier (voltage=310mV RMS and current 9.86mA RMS)”