1. Home
  2. tech-talk
  3. 147133-20253

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

Showing 10 responses by erik_squires

erik_squires OP
5,268 posts
 
It started with a bold claim from Carver stating his amplifier was indistinguishable from a tube unit.

His first claim was he could make it indistinguishable. Not that it started there. After that he produced amps such as the M500t. He may have produced others on this same idea, and it's arguable how well he succeeded.

His amp may ONLY have been an accurate reproduction of the CJ amp with 1 particular speaker. In any event, I don't claim his success, but I do claim his revolutionary way to evaluate equipment has not carried us forward, and that's disappointing.

one of which was increasing its current capacity significantly 

Not my understanding. Among other things, Carver increased output impedance, going the opposite way.


don't agree that most of our measurements are stuck in 1970 technology. The test equipment we have today is like comparing a Lotus to a Model T

Which has not actually revolutionized our understanding. We, the buying public, read reviews and measurements taken with test gear which can add more zeroes to the distortion measurements and more dB to the S/N measurements compared to that in the 1970s but we are not presented with revolutionary ways of understanding the performance of electronics and their audibility. 


Likewise, I don't agree that no one has made improvements in measurements.   Folks have, I just don't see them dumping their IP into public domain for their competitors to use.


It's quite plausible this is true, and that leaves us, again the buyers, in exactly the same place as if it didn't exist. We as consumers are stuck with 1970s definitions of electronics measurements, despite vastly superior measurement possibilities, disk storage space, CPU power to now investigate the dynamic performance of gear in entirely new ways.


Best,

E
erik_squires OP
5,268 posts
 
PS, you may be a little confused since I think Carver may have used the term "current source" to describe the difference. That  doesn't mean more current. It's a different operating principle than a voltage source.
erik_squires OP
5,268 posts
 
Thanks for the clarifications, @almarg I was not aware of the earlier testing with the ML, so my thinking about the current improvements was probably not accurate.

I appreciate your detailed and informative corrections!

What this keeps tickling me of is the Technics digitally controlled Class D amplifier. They use DSP to pre-correct issues the amplifier has with the load. Amplitude and phase issues Class D amps tend to have in the top octaves.

I wonder if today we couldn't make better models, or get a better idea of what amps are doing, in such a way that would allow us to pick a sound.

Best,

E
erik_squires OP
5,268 posts
 
@spatialking Apologies, I seem to have been very much in error. You were right. I was wrong.

Best,
E
erik_squires OP
5,268 posts
 
@maplegrovemusic


Erik - Douglas Schroeder just reviewed a amplifier that does what you are describing . Think it was a Goldnote amp . Something about changing the dampening factor by a switch . 

Yep, similar idea about Carver's challenge with the CJ. Nelson Pass has also written a little about using current source amps with certain types of woofers, with some interesting conclusions.


Best,

E


erik_squires OP
5,268 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
5,268 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
erik_squires OP
5,268 posts
 
What good would it do to recreate this test?

I'm not saying we should do so verbatim. I'm saying that this was a ground breaking test that brought together several aspects of amplifier performance in ways the Stereophile suite does not.

I'm saying it illustrates how limited we actually are in understanding how amps differ.

I don't agree that most of our measurements are stuck in 1970 technology. 

Can you name a new measurement since 1985 which has become part of the vernacular? 

I wish I had today's stuff back in my audio design days! 

Same. But adding precision is not a new measurement. It's just more precise.

Likewise, I don't agree that no one has made improvements in measurements.   Folks have, I just don't see them dumping their IP into public domain for their competitors to use.   


If true (not doubting it) that's at the core of our problem as end users.


Best,

Erik
erik_squires OP
5,268 posts
 
To give an example of what I'm talking about as really revolutionary, consider the system Meyer's sound labs uses to tune pro audio systems in real time as the audience arrives.


THAT is, relatively, revolutionary, and takes huge advantage of DSP and computer processing power to coordinate hundreds of speakers at a time.


Being able to push the noise floor from -70 dB to -100 dB is not. It's the same measurement, but with better gear. And as @elizabeth has pointed out, you can buy for a couple of hundred dollars what would have cost tens of thousands in 1985.
erik_squires OP
5,268 posts
 
i will add your list ignored the great contribution of Dr. Matti Otala...TIM


Sorry, I meant to type that but instead typed IM.

But ... 1970.
More to discover