@Kijanki ... thanks for your informative response. You wrote:
"Damping factor of 14 is OK. 8ohm speaker's impedance is mostly resistive. Assuming, that it is approx 6 ohm it limits effective DF to 1.33 . Amps DF of 14 will make it worse only by 9.5% - irrelevant."
In my case, I drive my speakers, which have roller coaster impedance and phase angle plots, off the 4 ohm taps. To my ears, those taps sound "overall" the best. While it may result in non-optimal impedance matching at higher frequencies, I surmise that the power demands place on the amp are not that significant at such frequencies. Further, as mentioned above, the amp has a very robust power supply. Hence, I doubt that the mismatch is resulting in considerable distortion.
Kinjank, you also write that:
"There is a lot of local NFB in almost every amp. Any resistance in cathode is a form of NFB. Global NFB doesn't have to create TIM if it is applied within certain limits. It improves pretty much everything - bandwidth, output impedance, THD & IMD. Great sounding amp with small amount of NFB requires great design and quality components. Unfortunately it is cheaper to achieve the same using cheaper design and excessive amount of NFB hence creating overshoots (odd harmonics in frequency domain) and unpleasant bright sound."
I surmised the same as posted above. I wrote that ARC said the use of NFB is part of an overall engineering solution that balances many variables.
Thanks again.
BIF
"Damping factor of 14 is OK. 8ohm speaker's impedance is mostly resistive. Assuming, that it is approx 6 ohm it limits effective DF to 1.33 . Amps DF of 14 will make it worse only by 9.5% - irrelevant."
In my case, I drive my speakers, which have roller coaster impedance and phase angle plots, off the 4 ohm taps. To my ears, those taps sound "overall" the best. While it may result in non-optimal impedance matching at higher frequencies, I surmise that the power demands place on the amp are not that significant at such frequencies. Further, as mentioned above, the amp has a very robust power supply. Hence, I doubt that the mismatch is resulting in considerable distortion.
Kinjank, you also write that:
"There is a lot of local NFB in almost every amp. Any resistance in cathode is a form of NFB. Global NFB doesn't have to create TIM if it is applied within certain limits. It improves pretty much everything - bandwidth, output impedance, THD & IMD. Great sounding amp with small amount of NFB requires great design and quality components. Unfortunately it is cheaper to achieve the same using cheaper design and excessive amount of NFB hence creating overshoots (odd harmonics in frequency domain) and unpleasant bright sound."
I surmised the same as posted above. I wrote that ARC said the use of NFB is part of an overall engineering solution that balances many variables.
Thanks again.
BIF