In addition to frequency response, what other parameters will affect the sound quality of the amplifier?

1. Distortion (THD/THD+N)
Total harmonic distortion (THD): The sound system amplifier will generate harmonics (such as 2f, 3f, etc.) outside the original signal due to nonlinear elements (such as transistors), resulting in a "burr" sound.

Impact --
When THD>0.1%, the human ear can perceive distortion, such as hoarseness of the human voice and loss of overtones of musical instruments; high-end Hi-Fi amplifiers need THD <0.01%.
THD+N (Total Harmonic Distortion + Noise): The circuit background noise is superimposed, which more truly reflects the actual listening experience. For example, THD+N may soar at high gain, resulting in an unclean background.

2. Signal-to-noise ratio (SNR): Determines the purity of the background
Definition: The power ratio of the useful signal to the background noise (unit: dB).
Impact --
SNR < 90dB: Noise (such as "rustling") can be heard in quiet passages, and dynamic compression;
SNR > 110dB: The background is like a "black curtain", and the details of weak sounds are clear (such as breathing and bow rubbing strings).
Optimization direction: Power supply filtering and low-noise components (such as JFET input stage) can improve SNR.

3. Output power and dynamic range
Rated power: It is necessary to match the speaker sensitivity (such as 84dB speakers need > 50W, 90dB only needs 20W), avoid under-pushing (weak sound) or overload (burning the speaker).

4. Other factors
Power supply rejection ratio (PSRR): Suppress power supply ripple interference, PSRR > 80dB can avoid "hum".
Transient response (Slew Rate): The rate of voltage change per unit time (V/μs). When <10V/μs, high-frequency transient distortion occurs (such as the cymbal's cracking becomes dull).
Temperature stability: Class A amplifiers drift at high temperatures, causing crossover distortion (intermediate frequency breakage).