Amazon.com: Dual OPA1622 SoundPlus Audio Operational Amplifier with a Low Noise Density of 2.8nV/Hz and a Low THD+N of -119.2dB at 1kHz,a High Output Drive of +145mA/-130mA for Direct Drive Headphone :
The low-noise ECC83 headphone amplifier circuit and el84 valve - Audio_Circuit - Circuit Diagram - SeekIC.com
Low noise headphone amplifier design
Headphone Audio Amplifier Circuit on PCB using LM386