The Bob Carver Challenge

Seeing the other Carver thread today reminded me of the Carver Challenge many years ago. Bob Carver claimed that he could take one of his inexpensive power amplifiers and make it sound like any other amp under blind test conditions, just by changing and tuning the basic design specs without materially altering the cost of the amp. The challenge was that his amp would challenge anything, regardless of cost.

Well worth a read:

http://www.stereophile.com/features/the_carver_challenge/

 

So, amplifiers do sound different then but it is possible to make them sound indistinguishable given enough time and skill.

 

What I found interesting then and now was the surprise for those involved one amp could be made to sound like another even with different topology. Throw enough know-how, parts and technology at a pocket radio and you can turn it into any high-end amplifier of your choice.

It was interesting to see a designer offer what appears to be repeatable procedures and measureable differences explaining some of the sonic differences between amplifiers. More articles like this should written in an effort to de-mystify and validate the claims that amps can and do sound different.

I also got a kick out of Stereophile's assumption that a 700 dollar amplifier couldn't be state-of-the-art (and one of the prime reasons why I don't read hifi magazines..they are as clueless as most everyone else in this hobby )

Top marks for resurfacing this old experiment Rob.

regards,

dave

 

Spot on!

That is a good article - I had forgotten it was Bob Carver. I though it was Tim D' P'.

 

Sort of, but too simplistic and it misses the point.

Amplifiers that sound different do so for well understood reasons, and a designer can alter those design parameters that alter the sound without for example, requiring a pretty standard and inexpensive design be replaced with something costing far more, or with completely different topology.

Carver's view is that where the measurements closely correlate, the amps sound the same.

 

I would love to see a designer exactly duplicate the sound of a berning ZH270 (or even better their bigger brothers) for seven hundred dollars.

I'd buy 3 !

Wonder why they haven't done that if it's so easy?

 

To my mind this is interesting only from an academic perspective. In the real world too many external variables exist, e.g. if you have say a Sugden A21SE, a Krell 300i integrated, a Leben CS300 and say Martin Logan SL3s (cripplingly low impedance), Klipsch LaScala (scarily efficient) and ProAc Tablette speakers (typical small stand mount) my guess is each amp would gravitate to a given speaker system pretty fast. It would be very easy to argue that the Krell was the 'best' amp here, as on paper it has huge current and high power that doubles perfectly as impedance is halved, along with low noise, low distortion etc etc, yet I'd bet money that the Leben would kick it into the weeds via the Klipsch. It would however be the only amp in the pack capable of controlling the SL3s. It's just not a level playing field out there in audio land.

Tony.

 

I suppose it doesn't sound that good to enough people to make it worth it. I understand it's quite a characterful amp.

 

People have different ideas on 'good' - and very much as Tony suggests there is certainly some synergy at play in some systems. I'd argue that in the vast majority of cases there is no need for synergy - it is only where one or more components has unusual specs.

For example, if you ran a Meridian CD player and say a pair of PMC passives, you could use most SS amps on the market with enough power for clean drive and have no meaningful change to the sound of the system. You cannot introduce a Berning into that system with no change - it might have the power but the output characteristics are unusual enough to alter the system performance. You may then need a different and more sympathetic speaker system....

Go back to what constitutes 'good', I'd take a £300 NAD integrated over £100k+ of Kondo. The former is designed to do a job of work, the latter overlays a sonic signature. I don't want signature from my electronics. Same with amps such as the Berning, though on that you can alter the signature to some degree.

What is key from the Carver article is that amplifier sound boils down to the simple manipulation of understood performance specs - not the adoption of boutique components, visualy simple/complex circuits, switches in the signal path, huge PSU overkill, case design and other such reasons given to justify performance.

 

Whilst I can understand the principle of changing a sonic presentation, I struggle with understanding how fiddling with an amp would improve the detail that is being obscured in a poorly designed amp so as to sound like a much better amp. I know that some newer designs try to emulate this with a lift in their treble regions, thus creating an impression of detail, but it certainly isn't the same as actually retrieving that detail.

On a similar note, just how do you go about changing the noise floor on an amp with simple "fiddling".

 

The only things I find I care about in audio these days are analogue sources and loudspeakers. Both need to be suited to both the listener's taste and surrounding environment. There are many radically differing options yet no right answer. The amp is the thing that allows these transducers to communicate, and as such it requires very careful consideration, but to my mind this selection should be made once these variables are known, i.e. you are looking for an amp that fits well between your chosen source and speakers.

Tony.

 

Hi Simon

I'd respectfully say we are one step removed from that.


I am priveledged through my industry contacts to have heard some of the best amplifiers in the world - amps with a cost running into tens of thousands of pounds.

The component quality in these amps are no-cost-spared, and often the circuit design is unique too.

These amps aren't copied simply because the amp designers / builders simply don't have hundreds of thousands of pounds worth of amps around to copy.

They don't know what they are missing in short.



There genuinely are amps out there that are in a different league to the masses.

Very few are priveledged to have heard them at home in a familiar system.
Very very few low-fi companies have such products as a reference to copy.

 

I've never bought the increased detail argument.
You can obscure fine detail and high distortion and high noise floor can certainly mask fine detail. However these things are not a challenge for any competent amplifier designer and something clean enough to 'get out of the way' can be built for a few hundred pounds.

A brightly lit tonal balance can give the impression of more detail, as can certain distortions as in small quantities they can sharpen the sound and make it apparently more analytical.

Listen to so called hightly detailed amplifers (those that measure well) against those without such reputations unsighted and you'll be surprised at the result.

On the issue of noise floor, you can alter this fairly simply in many amplifiers by changing the input series resistance. This is a source of noise and the higher the input resistance goes the higher the more noise (hiss) you can expect.
Reduce it and you cut noise on the input stage, but of course you then have to drive a low impedance. Fine if you can. Just one example where changing the value of just one component alters the noise floor.

 

I would disagree.

There are amps out there sounding different to the masses - but that makes them fundamentally wrong for most systems. The audible difference comes from technical inferiority.
Once you reach a certain performance bar - and that costs relatively little - you have two roads only ahead of you:

- Overkill and overspec. This takes the basic design and beefs it up. More power, improving already excellent specs to superb etc. These command a high cost premium but unless the power advantage is utilised offer no audible benefit.

- Go backward. Literaly, you start to fark the relative perfection you have already achieved in order to produce something that sounds different to the rest.
What are actually backward steps are sold as advantages and improvements. This is particularly the case with valve amps.
This is one of the few areas where two negatives can make a positive in terms of system matching.

I did a couple of interesting experiments at the London Bake-off show by making a Rega SS power amp sound more like a SE valve amp. All listening commented that this was effective. The parts for the gadget in question cost me £15 from Maplin. Now that does simplify the issue but it rams home the point that we are talking about exerting control over some basic specifications.

 

Hi Rob!

I think we simply totally disagree! lol.

At all parts of hifi, I have seen that better quality components make an audible difference. From capacitors and resistors, to transformers, speaker cones diamonds on cartridges.

Quality counts in short, and it's audible. The best designs with the best components cost more money, and they sound better too.

Design compromises always exist, but exist to a far greater degree when budget constraints kick in. I just read a review of a cheap DAC, and the manufacturers comments. They used Op-amps, but the designer said he would have rather used discrete transistors. The reason he said, was the price he was aiming for.

I simply don't believe you can get technical perfection by mass manufacture of cheap components. Cheap is cheap for a reason..

 

Hi Chris,

I have to disagree for the same reasons as Rob. Some of the super expensive amps are different, but not actually better. In some systems, and to some ears, that difference is an improvement. However it is generally easy to mimic in a far more affordable amp.

I'd put money on a bet that if you took a Berning amp, replicated the speaker load, knocked the level down with some resistors and fed it through a CA 840 amp, the resulting sound would be indistinguishable from a direct Berning to speaker connection in a blind test.

I say that because the CA 840 is so damn transparent it will easily replicate the characteristics of the Berning if they are fed in at the input.

 

why would you want to make a Berning sound like a richer sounds amp?

do it the other way, and you'll have something worth talking about..

 

That is what I am talking about. Feed the output of the Berning through the CA 840 and I bet it still sounds the same as the Berning.

If you have a Berning, we could always do a bake-off and test the theory. I don't have a CA 840 but I could do the same with my Cyrus 3.

 

hi

unfortunately not.

My power amp is pretty good, but not as good as I have heard from some amps.

I'm delighted to hear you and Rob can replicate the best amps on the planet with a handful of resistors.

I think you have a new calling?

 

Which amps do you think of as the best? Berning obviously, and?