American Grado RA1 headphone amplifier

The earphone is directly preamplified and amplified by IC1, which is suitable for op amp ICs with relatively large output current, such as JRC4556 and AD8397. However, these ICs generally require a higher operating voltage (at least 6V) to improve the sound quality.

The headphone amplifier gain G=1+R3/R2=4 (times), so the maximum voltage amplification factor of the headphone amplifier is 4 times, and the power amplification factor is approximately 16 times.

The low-frequency cutoff frequency of the headphone amplifier is fo=1/(2×PI×C1×R1)=6.6Hz, PI=3.14, C1 should be converted from μF to F, and R is in Ω. The low-frequency cutoff frequency of the headphone amplifier is generally 1~10Hz. If you don't like bass, you can increase fo to 20~100Hz.

The value of R1 should preferably be approximately equal to the parallel value of R2 and R3, otherwise the output may have a DC component.