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In Reply to: RE: Might be worth reading... posted by Doug Schneider on December 02, 2020 at 05:24:04
Might be worth reading via the link below.I am quite familiar with Putzeys and his work - along with using one of his Ncore amplifiers for the garage system. Arguably, his designs are the best switchers available today. While it has a wonderful midrange, I find the top end is compromised as compared with the VTLs. But it works great with New Advents and having 300 watts/channel on hand provides nice headroom. Lots of bang for buck but have no interest with it driving the stats in the main system.
As well, you might want to ask yourself this: If a product can't perform well on "simple" sine-wave tests, how is going to perform well under supposedly more complex conditions?
It's not a case of inherently linear design not performing well on sine wave tests. Rather - how many zeroes to the right of the decimal point actually improve the listening experience? Nelson Pass has demonstrated that such an assertion has reality bass-ackwards. Designs using boatloads of cascaded feedback do downright poorly on complex conditions. Here is a visual from the referenced article:
As for me, I'll pass (pun intended!) on introducing complex distortion products for which the ear is more sensitive. Some feedback can be good, but lots is not necessarily better when the objective is determined by what you hear - as opposed to what you see on paper.
Which is likely why I am not a fan of op amp based designs as they have complex topologies and rely upon large amounts (>40db) of corrective feedback. Have you ever replaced such with discrete FETs and compared the differences? I found them very enlightening with a Music Hall DAC where I replaced three TI chips almost three years ago with Burson FETs.
My home theater/MC system uses Emotiva and Oppo products with TL072 and 5532 op amps, respectively. The result is neutral, but opaque sounding as compared with the Audio Research combination used upstairs which are zero feedback, class A designs using matched JFETs and triodes in the case of the SP20.
Edits: 12/02/20Follow Ups:
You might enjoy this book. Yes, it's technical but not loads of math. Dr. Kolinummi has sections describing in engineering terms why steady state distortion measurement is hardly a complete examination of audio performance.
As Nelson observes, it differs from other analyses of distortion by looking at open loop linearity - an area in which switchers and op amps are weak.
They require heroic amounts of correction to behave properly.
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