Comparison CJ MV-55 & 11A

Boy we seem to have consistency on this one.
I used both amps with Acoustat 1+1s. I preferred the MV-55 to the 11A in all ways except for the bass which was more powerful and more tightly controlled with the 11A. Other than the bass... no contest.

I compared these two amps on several Proacs, and also the CJ 12's. The comments above are exactly right. The Proacs definitely benefit from the additional power of the 11a, and the 11a sounds more detailed, correct and refined overall. But that EL34 midrange magic of the '55 is not as present in the 6550'd 11a. Also the lack of power of the '55 results in a looser bass, which is definitely less accurate, but can be pleasing if your system is bass-shy.

The MV-55 would sound beautiful with the ProAcs. I once had an urge to upgrade to the 11a but in direct comparison I preferred the sweet midrange magic of the MV-55 with its equally sweet and liquid treble. The 11a was more dynamic and a little more transparent but some of the midrange magic was gone.

I used both amps with Response 2 for one year each. I was very pleased with both. I think the speaker would benefit from the additional power provided by the 11a, but you do lose the some of the mid band sweetness from the EL34 tubes. By contrast, the 6550 is a better all round performer.