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Interesting post from diyaudio....

Posted by kuribo (A) on December 18, 2014 at 16:22:04

Brings to mind the comments made by Bruno Putzeys of Hypex who said he could make an amp sound like any other but he preferred to design his amp to be as neutral and transparent as possible.....

Carver Challenge Details...

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For those who might be interested, I dug up the Carver Challenge article in Stereophile. The brief background is Bob Carver (the man behind Phase Linear, Carver and now Sunfire) made it known to the press he would put his inexpensive amplifiers up against ANY amplifier in a blind test if he had a few days to adjust the transfer function of his amp to match the challenger's amp. Stereophile took him up on the challenge and here are some quotes from the article written by J. Gordon Holt:

"We knew that Carver couldn't possibly pull this off, at least not to the point where none of us would be able to distinguish between his modified 1.0 and our reference amp. After all, some of the most highly trained audio ears in the world would be listening for the differences."

"...the reference unit is a high-powered, very expensive stereo unit with a strong and unique sonic "personality" and a penchant for being very finicky about the loudspeakers it works with. It was, we were gleefully confident, likely to be very dissimilar in sound from Carver's own designs."

"Not surprisingly, the reference amplifier sounded very different [from the Carver] and, in our opinion (shared, in most respects, by Bob), much better."

"Bob didn't have to concern himself about quality capacitors, minimal internal wiring, gold connectors, or any of those things; all he needed to do was duplicate, at the output of his amplifier, the sum of their effects at the output of the reference amp. Once he had obtained the necessarily deep null between those amplifiers, it was his belief that ears were not going to pick up on what was left."

"After the second day of listening to his final design, we threw in the towel and conceded Bob the bout."

"We had thrown some of the most revealing tests that we know of at both amps, and they came through identically. Even on the subliminal level--the level at which you gradually get the feeling that one amplifier is more "comfortable" than another--we failed to sense a difference between the two amps."

"We wanted Bob to fail. We wanted to hear a difference. Among other things, it would have reassured us that our ears really are among the best in the business." (italics emphasis in original article)

"According to the rules of the game, Bob had won."

"The implications of all this are disquieting, to say the least. If, after only four days of work, it is possible for someone--design genius or not--to make a $700 amplifier sound exactly like a state-of-the-art amplifier costing many times as much, what does that say for the cost-effectiveness of the latter?"

The amplifier used was a Carver M1.0 selling for $699. Bob used null difference testing to tweak the M1.0 until he obtained a deep null with the (unnamed) Stereophile tube reference amp. They did not reveal the reference amp because they felt it would be unfair to that manufacture who might ask: "why us?".

It was later revealed the most significant modification Bob made was to simply put some series resistance into the output of the M1.0 to better approximate the much higher output impedance of the tube amp. The other tweaks were supposedly limited to a small R-C network in the feedback loop.

It should be noted that J. Gorden Holt was the Editor-At-Large and Chief Tester at that time. Larry Archibald, the Publisher, and John Atkinson, the International Editor and a frequent reviewer, also participated in the listening sessions.

The challenge showed two things IMHO:

1 - It validates null difference testing with "some of the most highly trained ears in the world". Bob simply nulled his amp to the reference and JGH, JA and LA at Stereophile could not tell them apart.

2 - It shows that you don't need expensive components or exotic techniques to make a very modest amplifier with mainstream parts sound like a much more esoteric amp.

Bob literally bought the components used to modify the stock M1.0 at Radio Shack and worked out of his hotel room in Sante Fe (home of Stereophile). He made a 20 pound (9kg) mass production solid state power amp full of cheap parts (with a rail switching class-G power supply no less) sound so close to a very expensive heavy monster tube design that some of the mightiest GoldenEars couldn't tell them apart.

Considering that Stereophile is mainly filled with ads from high-end vendors hurt by the outcome of the challenge (versus just one advertiser--Carver helped by it), and that everything would point to the editors not wanting to admit a $700 amp can sound the same as a five figure one, I have to assume they wrote an accurate article and were not paying Bob any special favors.

Edits: 12/18/14

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