Would switching amps make a big difference?

@cdc2

Excellent suggestion by Ralph (Atmasphere).

In the absence of a Zero autoformer, though, I would just say that the amplifier output impedance should be a good deal lower than the numbers I cited for the Prologue Seven, which btw correspond to a damping factor of approximately 1. Beyond that the sonics of the specific amp, and how they would synergize with the sonics of the speaker, would be the predominant consideration.

Very often amplifier output impedances are not specified (although if Stereophile has reviewed the amp the measurements section of the review will provide those numbers), but damping factors often are specified. And as you may be aware damping factor is inversely proportional to output impedance, and corresponds at least theoretically to the load impedance for which a tap is designated divided by the output impedance of that tap. So the output impedance of an 8 ohm tap should approximately correspond to 8 ohms divided by the damping factor; the output impedance of a 4 ohm tap should approximately correspond to 4 ohms divided by the damping factor, etc.

I suspect that a damping factor of at least around 8 or so would be preferable with your speakers, if a Zero is not used.

Manufacturers of tube amps having relatively high damping factors/relatively low output impedances include Music Reference, Audio Research, and McIntosh. I would be careful about preamp-to-amp impedance matching, though. I couldn’t find an output impedance spec for your preamp, but the Music Reference RM-200, which I suspect would be a fine match in other respects, has an input impedance of 30K balanced and 15K unbalanced. That is too low to be optimal with some tube preamps. Contact the preamp manufacturer if in doubt about that.

Good luck. Regards,
-- Al

Any owners of Martin Logan speakers using tube amps want to weigh in?

I've heard our amps in several customer's homes using our amps. But all of them were also using the ZEROs. No problem playing the highs at all.

If you like the Martin-Logans with tube amplification, you might not like them with solid state.  It might be more accurate, but it will be different than what you have now.  If your room can handle them properly, get the Impression 11a loudspeakers first and then sort out the amp situation.  The ARC room correction will elevate your system performance.  That said, at the level of components you already have, $5k upgrading your source inputs coupled with acoustic room treatments is money better spent than an amp or loudspeaker switch.

Any thoughts on which tube amps work best with Martin Logan speakers?