What amp should I buy to power Martin Logan Esl's?

Thanks Bombaywala -- very good explanation. After breaking big rocks with a sledge hammer, courtesy of Ralph and Al, I'm starting to better understand speaker/amp electrical matching. Of course, I've also come to better understand that speaker and amp designs are often the result of engineering/technical compromises. I believe Al and others made that point as well many times.

One such compromise that comes to mind is the benefit and cost associated with using negative feedback. Ralph and Al have spoken about many of the costs, such as TIM distortion and odd ordered harmonic distortion. They have also mentioned some important benefits, such as lower overall distortion, increased bandwidth and lower output impedance.

Case in point: I believe that ARC uses NF in most (if not all) of its tube amps. For example, the somewhat new ARC Ref 150 tube amp uses 14 db of NF and has approximately 1.1 ohm output impedance off the 8 ohm tap and about 60% of that value off the 4 ohm tap. See Stereophile/John Atkinson Ref 150 bench test last year.

Not sure if that turns a low impedance/high capacitance ESL speaker into vanilla ice cream for the Ref 150. Not even sure if the Ref 150 likes ice cream. But I wonder how well tube amps that use NF fare with ESL loads.

08-06-13: Bifwynne
Thanks Bombaywala -- very good explanation.

thanks for your kind words Bifwynne.

But I wonder how well tube amps that use NF fare with ESL loads.

I would think that tube amps using large amts of NF would fare quite well with highly capacitative loads from a purely electrical interface point-of-view. As mentioned by you in your post, NF would make the power amp measure really well on the testbench. I would think that you would get pretty decent sonics from a high-NF tube amp but what would be missing would be the soul of the music. I think that a high NF tube amp would never truly 'sing' to the music - it would have many of the audiophile attributes but would sound very clinical & non-engaging.

I forgot to write in my prev post - comments from other members who have experience with tube amps driving highly capactitative loads are most welcome. Hopefully I'm the person with the least amount of knowledge on this topic. Thanks.

Bombaywalla, not sure what constitutes "large amounts of NF," but the ARC Ref 150 uses 14 db of it. Perhaps somewhat responsive to the issue of tubes and ESLs, ARC reports (and Atkinson confirms) that output regulation is approximately +/- .5 db off the 4 ohm tap. So ... maybe the amp may add a touch of "flavor" to the acoustic presentation, but who said life is perfect.

Can't say that I recall reading comments that the Ref 150 doesn't sing to the music, but I'm tone deaf. What do I know??

I suppose we still don't know for sure what all the techno-babble means in real life. So I echo Bombaywalla's request that folks who have matched tubes and ESLs report their real-life experiences. Kinda' an interesting topic.

Bifwynne,
In my post I did not intend to single out the ARC Ref150 (which I understand is of personal interest to you due to your ownership). I was referring to the tube amp-ESL match in general so as to not hijack the OP's thread. Thanks.