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RE: December Stereophile - Allnic D-5000 DHT

Posted by rick_m (A) on November 24, 2014 at 09:01:42

In Reply to: RE: December Stereophile - Allnic D-5000 DHT posted by FSonicSmith on November 22, 2014 at 08:39:43:

"Why assume that JA is even measuring the right things?"

He certainly does measure the right things. Just not enough of them...

Basically those sorts of measurements largely just confirm that the units aren't "broken" although in the case of really poorly performing stuff, like most tube designs, they have more significance. And that's quite appropriate for a review magazine since it would be a waste for everyone if the test unit was overtly malfunctioning and that's more likely to happen with very early production units which are the usually the ones that get reviewed since everyone involved, including me, wants to know about new stuff while it's still "new stuff".

Now don't get your panties in a wad about my characterization of tube designs as poorly performing. It's sort of ironic, but logical if you ponder it... tubes were our first active devices and the measurements we devised to test and characterize designs using them were oriented to detecting the sorts of problems that they were prone to, largely non-linear transconductance. Since they didn't have a lot of gain-bandwidth they were usually ran open loop making their transfer function a significant part of the unit's. The next worse thing was the transformers.

OK, so we needed someway to work on these designs and someone, I know not whom but it might have been at Hewlett Packard, devised a "distortion analyzer". What they do is just notch out the fundamental on the premise that what's left is distortion. Well distortion and noise but noise is sort-of a form of distortion. The result was a measurement that had a good corrolation with perception. It was felt that the higher orders of distortion weren't as important as the second and third harmonics because our hearing tapers off and the slugish tubes and leaky transformers attenuated them anyway.

Well, that was then... Today it's another story, but still we cling to the old paradigms. Solid state devics are way faster but have hideous transfer functions compared to tubes. BUT they are orders of magnitude more efficient and reliable. There's no free lunch.

I don't know of any measurement schemes in common use that reliably correlate well with our perceptions and sensitivities of the higher order and temporal issues that readily arise with the newer components and circuit topologies. I do believe that work has been done in those areas but...

So back to Stereophile, decades ago I raised the issue of them not measuring PSRR (how well power supply anomolies are ignored) during a panel at one of their shows. JA was there but the chap who answered (don't recall his name) said that the problem was that there wasn't a standardized methodology or tolerance level. Well, that makes a certain amount of sense, but later JA didn't let that stop him when helping to bring jitter to the table as a significant new problem.

My point is that measurements are, in general, a force for good, but how effective of a force they are depends on their corrolation with the mechanisms affecting final outcome. So I DO understand why many audiophiles believe them to be garbage, but they are wrong...

Rick

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