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Critic's Corner Discuss a review. Provide constructive feedback. Talk to the industry. |
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Critic's Corner Discuss a review. Provide constructive feedback. Talk to the industry. |
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In Reply to: Understood, but ... posted by 13th Duke of Wymbourne on November 13, 2015 at 15:36:24:
". it shouldn't become a hall-pass for designers to not do a good job." If it measures good and sounds bad does the designer get a pass for producing excrement with good specs?
Define not doing a good job, please.
"ou can't help getting high 2HD with something like a single-ended triode so how much care/knowledge does the designer really need?"
Very much actually because the goal is to keep the distortion low order and prevent the rise in high order harmonics...this means a lot of care in the design of each stage of the amplifier and careful balancing of operating points, passive parts choice and most importantly using a great transformer (at least the best that is affordable for a given design price point). It is a lot harder than making a mediocre design and cleaning it up with copious amounts of negative feedback.
" I do wonder whether high levels of consonant distortion"
Let me be clear, there is no such thing as "consonant" distortion...all distortion degrades fidelity but some does much more damage at much lower levels than others. Read the articles in Stereophile by Keith Howard where he added different distortion patterns to different music selections. He found no added distortion was the best (no surprise) but he also found that some patterns were far worse sounding than others. The monotonic pattern that was championed by Hiraga was found to be the least offensive of the distortion patterns he tried. This is the same pattern that Cheever concludes should be the least audible and that Geddes data also corroborates. Now, ideally we have a linear amplification device that gives no additional harmonics or IM distortion but since all our devices are "bent" then that ain't going to happen.
JA often calls triodes without feedback "bent" but the truth is that the triode is the least "bent" of all amplification devices, with the BJT and the Pentode being the most "bent". That is the true reality.
I think the white paper from Nelson Pass regarding negative feedback is interesting and illustrates quite well what is wrong under the surface. You don't really get rid of distortion but you seem to just push it around...Crowhurst said that the result is a kind of signal modulated "noise" floor that will mask low level resolution and damage dynamics.
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Follow Ups
- RE: Understood, but ... - morricab 11/14/1513:12:24 11/14/15 (0)
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