The smoothest amp you've heard?

Smoothest most detailed amp into a pair of Quad 57’s with Kelly Decca Ribbons tweeters from 12khz up, for me would have been a Nelson Pass Pure Class-A 20w project amp I made called the A20, back in the 80’s
https://www.firstwatt.com/pdf/art_classa_20.pdf
This amp led me later to make a self contained recirculating water cooled monster, which was >100w of the same thing, and a two man lift.

Cheers George

All the tube amps I've heard, pretty much all sound very close..If that makes sense.
Speakers make allllll the difference. 
Which is why I am a  WBer cultist. 

Ayre may be that.

It has this weird ability to suck noise out of a room.... you have to hear it for a while to get what I mean.

Luxman L-509X.  Too smooth.  

many tube amps are closed in on top, not airy. so they may be butter smooth, but it’s a circuit artifact overlayed over all the music, and not ’the’ music.

what you want is transparent, grain-less and continuous, but still lively and with great textures, timbres and tonal richness. i’d choose darTZeel; both the dart 108 stereo Mk1 and Mk2, and the dart mono blocks. zero global feedback, minimal parts count in the signal path. purity and transparent. no sense of any artifact overlay.....just music. super smooth and amazingly grain-less and extended, airy top end.

darTZeel does not sound like tubes, or solid state.....it sounds like music.