Do amp's sound different?

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What a silly question. Of course they do. I am certain no reasoned person, engineer or audiophile, would argue that a solid state power amp sounds identical to a same-wattage tube amplifier. They're just so different that you can easily hear (and measure) those differences. But if two amps of radically different topologies sound different, can they be made to sound the same? This very question was posed to the affable Bob Carver in 1985 and became the basis of one of the oddest challenges in audio history. In 1985 Stereophile magazine was edited by J. Gordon Holt and published by Larry Archibald. (John Atkinson was still editing HiFi News in the UK and wouldn't take the reins until one year later.) As the story goes, Carver, sometimes known as Captain Bob for his signature blue cap with a gold anchor emblazoned on the front, bragged to Larry Archibald "that he could make his $700 Model 1.0 amplifier sound "indistinguishable from" any amplifier of Stereophile's choice", Larry took him up on the challenge. This became famously known as The Carver Challenge. What Bob did was simple in concept, yet difficult to do without the enormous wealth of knowledge Carver possesses. Bob performed a null test where two gain matched amplifiers are fed the same signal before their outputs are summed together in a difference amplifier. Were the two amps identical the measured differences would be zero. But, because all amps sound different, those differences show up on an oscilloscope or metering system in varying degrees, depending on how big the differences between the two are. Bob then used his extraordinary skills to tune his amp to match that of the Conrad Johnson Premier Five to a null of -70dB and, lo and behold, the two amps sounded the same. The Stereophile listening panel was astonished that he could manage such a feat and the challenge has gone down in audio history. It's worth reading the article again, which you can do here. I've also put a video together with a slightly different bent, but on the same subject. You can watch that here.
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Paul McGowan

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