Tube Pre/ Class D Amp - Who has done it?

In some cases I believe this is to allow for the OEM to produce their own high impedance input stage.  If you make pr eamps, maybe worth taking a gander at incorporating your own front-end. :) 
 

Thats what we have done with our Hybrids. 

That’s what we have done with our Hybrid amplifiers. One uses a DHT input stage. I didn’t want to go to far into that as didn’t want the post to look like a promo. 

@erik_squires 

The seemingly consistent feature among previous generations of Class D amps has been relatively low input impedance. 

FWIW the input impedance of our class D amps is 100K single-ended or balanced. Anything can drive them.

So - I’ve been (re)assembling my cabin system. It now consists of the Atmasphere MP-1 mk 3.3 preamp (tube) and Atmasphere Class D monos and I’m pleased to say it’s a very good combination. It’s different than my primary system which is solid state preamp going into a class A/B amp but they’re both very satisfying even though they bring different things to the table. 

I’ve had class D amps before (PS Audio Stellar S300, NAD M22, NAD M33) but they all failed to fully satisfy. They weren’t bad, but they also weren’t that great and I’ve since sold them. The Atmasphere Class Ds are notably more musical and a terrific value. I will say they’re not quite as good as my Class A/B amp to which i directly compared them. But they were also a LOT less expensive. 

So, my recent experience is a tube preamp/class D combo is a nice pairing. 

I have been testing our various tube preamps with GaN FET amps and our hybrid  amps (one uses a 12AU7 input stage while the other uses DHT-currently running 2A3’s)

Being a bit biased, my preference is our 2A3 only linestage. The GaN FET modules on their own have a 100K input impedance and the hybrids are min. 100k
The 2A3 preamp utilizes transformer coupled inputs with single ended output  

With the higher input impedance and the better quality of todays Class D amps, it is not to hard to get the sound you want with a tube preamp  just be careful with the synergy with high output preamps with some Class D/solid state low impedance inputs. As always  

I am using the LTA Aero DAC, LTA microZOTL Level 3 preamp, and Apollon Audio PET950 dual mono Purifi amp. Driving DALI Epicon 6's plus a pair of Rythmik F12G-SE subs. The LTA components provide the right level of tubiness, without the transformer-induced distortion at frequency extremes. I am in love with the sound of Ken Rad VT-231 bg 6SN7s in this rig.

My initial impressions were comparing a Pontus II, Primaluna pre + power amp to the Pontus II, Primaluna pre + Apollon power amp.  At first blush, things seemed a little dead and two dimensional, but some fiddling with EQ (minor bump to midrange) solved some of that. Allowing some time to get used to the new sound also helped. The grip and precision on bass is absolutely phenomenal with the Apollon, and the rest of the range is very smooth. I would say top end was also significantly better in definition and air.

I believe the uncompromising neutrality of the Purifi amp exposed weaknesses in the Primaluna. Switching out the DAC and pre for the LTA components was (unsurprisingly) a tremendous step up. Now I'm quite happy with soundstage, tonality, and imaging. It is very musical, and listening sessions always run much longer than budgeted...