I'm friends with a physicist named Earl Geddes who specializes in acoustics and psychoacoustics, has authored books and holds patents in the field, and who not long ago presented several papers to the Audio Engineering Society on the subject of distortion perception. Earl is NOT a tube-o-phile.
Earl's research confirmed that the ear is very sensitive to low levels of high order harmonic distortion (I don't recall whether he singled out odd-order distortion or not), but very tolerant of high levels of second harmonic distortion. He also found that the ear is very sensitive to a rise in distortion at very very low power levels.
After he had completed the study, Earl made this remark to me (as close as I can remember): "Duke, now I see why you and your friends like tubes so much". He also told me that his study indicates a negative correlation between THD and listener preference - in other words, listeners were more likely to prefer the device with the higher total harmonic distortion measurement! The reason is, the THD measurement does not correlate well at all with distortion perception. THE INDUSTRY IS MEASURING THE WRONG THINGS.
Earl Geddes and Lydia Lee have proposed a new distortion metric that correlates very well with subjective listening tests, but it has not been embraced by the industry.
Anyway, my point is that in general solid state devices have lower measured distortion, but the distortion characteristic of tube devices is more in harmony with the way our ears work.
Finally, as an Atma-Sphere dealer, I have never had a customer's Atma-Sphere amp or preamp "blow up". Tube failure is not an amp blowing up, and Ralph's amps are designed so that tube failure does not damage the amp at all. In several thousand hours of listening, I have had one case of output tube failure and one case of input tube failure in an Atma-Sphere amp, both of which were easily remedied by replacing the tubes with no damage to anything. Ralph has never had a case of a customer's amp "blowing up", so I think Raul overstated his experience a bit.
Duke
Earl's research confirmed that the ear is very sensitive to low levels of high order harmonic distortion (I don't recall whether he singled out odd-order distortion or not), but very tolerant of high levels of second harmonic distortion. He also found that the ear is very sensitive to a rise in distortion at very very low power levels.
After he had completed the study, Earl made this remark to me (as close as I can remember): "Duke, now I see why you and your friends like tubes so much". He also told me that his study indicates a negative correlation between THD and listener preference - in other words, listeners were more likely to prefer the device with the higher total harmonic distortion measurement! The reason is, the THD measurement does not correlate well at all with distortion perception. THE INDUSTRY IS MEASURING THE WRONG THINGS.
Earl Geddes and Lydia Lee have proposed a new distortion metric that correlates very well with subjective listening tests, but it has not been embraced by the industry.
Anyway, my point is that in general solid state devices have lower measured distortion, but the distortion characteristic of tube devices is more in harmony with the way our ears work.
Finally, as an Atma-Sphere dealer, I have never had a customer's Atma-Sphere amp or preamp "blow up". Tube failure is not an amp blowing up, and Ralph's amps are designed so that tube failure does not damage the amp at all. In several thousand hours of listening, I have had one case of output tube failure and one case of input tube failure in an Atma-Sphere amp, both of which were easily remedied by replacing the tubes with no damage to anything. Ralph has never had a case of a customer's amp "blowing up", so I think Raul overstated his experience a bit.
Duke
