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The Carver Amp Challenge and the 21st Century and it's Failure

Some of you may be old enough to remember this article from Stereophile. Bob Carver claimed he could make an amplifier audibly indistinguishable from some of the best from Conrad Johnson. A high efficiency (not class D), solid state linear amp vs. a linear tube amplifier.


https://www.stereophile.com/content/carver-challenge


Carver's approach was to feed a speaker via both amps at the same time using opposite terminals. The speaker itself was the measure of accuracy. Any difference in output between the two amplifiers would cause audible output.


What's super important here is Carver invented a new way to measure the relative difference of amplifiers with a real load.


That's kind of revolutionary from the standpoint of commonly published measurements of amplifiers before. Steady state, frequency sweeps, THD, IM and S/N all failed (to my ears) to express human experience and preference. I remember a reviewer for Audio, I think Julian Hiirsch, who claimed that these primitive measures were enough to tell you what an amplifier sounds like. The man had no ear at all, in my mind.  More here:


https://www.soundandvision.com/content/reconsidering-julian-hirsch

And here was Carver in 1985 cleverly showing that two amplifiers which measured reasonably well, sounded differently. We should also be in awe of Carver's ability to shape the transfer function on the fly. That's pretty remarkable too but not the scope of this post.


My point is, really, Carver showed us a revolutionary way to examine differences between gear in 1985 and yet ... it did  not become widespread.  << insert endless screaming here >>


As far as I know (and that is very little) no manufacturer of any bit of kit or cable took this technique up. We are still stuck in 1985 for specifications, measurements and lack of understanding of what measures cause what effects and end up cycling through cables and amps based on a great deal of uncertainty.


My points, in summary:

  • Most of what we consider state-of-the-art measurements are stuck in the 1970s.
  • There are a number of ways to improve upon them
  • No one has.
  • We should be a little more humble when asserting if it can't be measured it isn't audible because our measurements are not nearly comprehensive
  • I look forward to manufacturers or hobbyists taking modern equipment to pursue new measurement and new insights into our hobby.


Best,
E


erik_squires
tomic601's avatar
tomic601
12,986 posts
 
There is a lot going on... the how with reliability ( never a Carver strong suite imo and experience running a service department in a college town ) may not be shared much because it is valuable IP and patents are expensive and not always worth it...

the amp I am listening to has five parts in the signal path, no emitter resistors, floating ground outputs, tube front end, liquid cooling so bias is a set point, ten regulated power supplies, built in HRS isolation.... etc, etc.....

the null test works well in an anechoic chamber to match pairs of speakers.... but so few do it....the reason why ? Well first ya need a chamber, and when they don’t null out, ya got to know what to do, and want to do something about it vs just passing it along....

color me fanboy :-)
tomic601's avatar
tomic601
12,986 posts
 
Good post Erik
erik_squires OP
16,281 posts
 
the null test works well in an anechoic chamber to match pairs of speakers.... but so few do it....the reason why ? Well first ya need a chamber, and when they don’t null out, ya got to know what to do, and want to do something about it vs just passing it along....


We could just as easily today measure the difference via the speaker terminals, and listen to it with headphones, or save it for spectral analysis. Carver was surely using a scope to figure out exactly what was going on and zeroing in with help.

erik_squires OP
16,281 posts
 
I also don’t want to get hung up on the null speaker test, because I think there are a number of ways to get more data and be more accurate.


I wanted to point out this test came out in 1985, and nothing in popular reading has come out since its equal or better. That’s what I call stagnation. What the Carver amp challenge shows is the space available for innovation and research. To stop now is like stopping astronomy when we see the moons of Saturn for the first time. "Hey, that's all there is!"


Best,

E
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