I agree with TLS49. I would go further and say, as someone with an extensive technical background and someone who certainly recognizes the value that specs can provide (especially in identifying combinations of components that are likely to be poor matches with each other), that THD numbers for amplifiers are generally worse than useless.
Extremely low THD numbers are commonly accomplished by heavy-handed application of feedback, which in turn will worsen Transient Intermodulation Distortion (TIM), which is not normally specified, and for which I believe measurement standards have not been defined. And which well respected researchers, starting with Dr. Matti Otala (who is generally credited with first identifying TIM during the 1970s), as well as many respected high end designers, consider to be more relevant to music reproduction than sine wave-based THD measurements.
Also, THD numbers say nothing about the DISTRIBUTION of the distortion among different harmonics. It is well established that extremely small trace amounts of certain odd order harmonic distortion components will be vastly more objectionable than much larger percentages of low order even harmonic distortion components.
Basically, IMO, the only potential usefulness of THD numbers is that they can suggest caution in choosing an amplifier having exceptionally "good" numbers.
Regards,
-- Al
Extremely low THD numbers are commonly accomplished by heavy-handed application of feedback, which in turn will worsen Transient Intermodulation Distortion (TIM), which is not normally specified, and for which I believe measurement standards have not been defined. And which well respected researchers, starting with Dr. Matti Otala (who is generally credited with first identifying TIM during the 1970s), as well as many respected high end designers, consider to be more relevant to music reproduction than sine wave-based THD measurements.
Also, THD numbers say nothing about the DISTRIBUTION of the distortion among different harmonics. It is well established that extremely small trace amounts of certain odd order harmonic distortion components will be vastly more objectionable than much larger percentages of low order even harmonic distortion components.
Basically, IMO, the only potential usefulness of THD numbers is that they can suggest caution in choosing an amplifier having exceptionally "good" numbers.
Regards,
-- Al