There is no need to make it complicated.
One opamp OPA1655 will drive 18R headphone.
Because it can deliver 100 mA.
It has ultralow distortion.
Like this
One opamp OPA1655 will drive 18R headphone.
Because it can deliver 100 mA.
It has ultralow distortion.
Like this
This is a 3 transistor Class A design.
The output shown is 10mW (+20dB) into 18R.
The distortion pretty low at this level = THD 0.001%.
Such an amplifier has been built successfully by other members.
Prefer to use a regulated power supply, like with LM317.
The output shown is 10mW (+20dB) into 18R.
The distortion pretty low at this level = THD 0.001%.
Such an amplifier has been built successfully by other members.
Prefer to use a regulated power supply, like with LM317.
This is the single-channel version of the OPA1656 (presumably good idea for thermal issues to use single channel per device). Its ultra-low distortion is characterized for 10k, 2k and 600 ohms, at 18 ohms it may surprise - distortion is likely to rise a lot with such a hard load. Besides 100mA is the short circuit current, not the maximum operating current. I'd suggest an opamp driving a current buffer (which can be discrete) is a better approach, opamp provides the linearity, current buffer handles the current.
The hard part is identifying a suitable current buffer arrangement - should be some examples out there of opamp/current buffer combination, its not an uncommon requirement.