I owned an A21, and it is an excellent amp. I use three JC 1 monoblocks to drive a pair of KEF Reference 107/2s and a 204/2C. These amps show the KEFs to great advantage. Immediately noticeable was the more-felt-than-heard low pedal notes from pipe organ recordings, the same experience I get with live recitals. And then there's the overall transparency these amps provide. I suspect it's the ability to deliver current that makes the JC 1 sound so great. I run mine in low bias mode which I think is Class A to 10 watts, because they got quite hot when run in high bias mode which I think remains Class A to 25 watts.
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