Several factors can affect the sound quality of a headphone amplifier:
Circuit design: The circuit design of the amplifier can have a significant impact on its sound quality. A well-designed amplifier will produce a clean and detailed sound, while a poorly designed amplifier may introduce distortion or other artifacts into the audio signal.
Power supply: The power supply of the amplifier can also affect its sound quality. A clean and stable power supply is important for producing high-quality audio.
Output stage: The output stage of the amplifier, which is responsible for driving the headphones, can also affect the sound quality. An amplifier with a good output stage will produce a clear and detailed sound, while a poor output stage may introduce distortion or other problems. The output stage quality is closely related to the circuit design and components adopted, e.g., the capacitors, resistors, ops and PCBs.
Digital-to-analog converter (DAC): If the amplifier has a built-in DAC, the quality of the DAC can affect the sound quality. A high-quality DAC will produce a clean and detailed sound, while a low-quality DAC may introduce artifacts or noise into the audio signal.
Noise and interference: Noise and interference treatments can also affect an amplifier's sound quality. Without proper design, the headphone amplifiers will bad signal-to-noise ratio and may produce a noisy or distorted sound.
In general, a high-quality headphone amplifier will produce a clean and detailed sound with minimal distortion and thus deliver high fidelity sound to the users. Paired it with good headphones will unlock the true potential of your headphones.