Anyone listen to Zu Audio's Definition Mk3?

My Hovland HP200 tube pre/Radia SS power amps are showing a good synergy with the 4s, and I'd really need to be convinced of the benefits of all tubes to make the pricey step up.
In the UK it's getting harder and harder to make meaningful audio comparisons, so I have to grab auditions when I can.
If I move from the Hovlands, my likely alternatives are the Atma Sphere S30/M60/Novacron or Dave Berning OTLs, and Audion Black Shadow 845 SETs.
Simon, the UK distributor of Zu really rates the Atma S30, maybe this is where I'll end up, certainly will be my easiest to arrange audition.

Gopher,
Your big tube SET vs OTL comments are astute.These are two different camps for sure.Preference and system will determine which direction to go.
Regards,

Charles, excuse my ignorance, but what are the salient differences between the two tube camps?
I had never got on with tubes full stop, being totally put off them by the stereotypical over warm wooly sound portrayed by BAT eg. But seven years ago got bowled over by the tube Hovland HP200 pre and found this sounded great with the SS Radia amp, servicing my Pro Ac Futures 2, then Zu Def2s and now 4s. Just love the combination of tube liquidity and SS neutrality.
Interestingly the 4s are so transparent and revealing I'm detecting a hint of hardness/coolness which I attribute to the SS Radia, and am really tempted to investigate all tube. Let me say this hardness is only a hint and may well be eradicated by careful choice of cabling (considering all Zu Event) rather than amp change.
So we have SET eg Audion Black Shadow, championed by Phil v OTL eg Atma Sphere championed by UK Zu dealer/Dave Berning ZOTL, much favoured by Roy Gregory in the detailed review of the Def4s in Audio Beat.
How do their respective pros and cons stack up, esp. in respect to listening thru the Def4s, with a very neutral revealing front end (in my case direct rim drive tt with air bearing linear tracking arm Trans Fi Salvation/ Terminator T3Pro)?

Hi Spirit,
I could relate to Gopher`s comment based on my own experiences, but keep in mind system synergy is key.I find the Atmasphere can come off very clear,fast and transparent but also lean and thinner in some systems.In comparison the 845 SET ampsI`ve heard are fuller in body and tone with more presence and flesh on the bone,yet as detaied(not dark,slow or veiled).Depending on one`s needs or wants 'either' could be the right choice.

Some will say the SET has more pleasing distortion(2nd order)to account for this perception of fullness of tonality.Maybe, but I`m always struck by the full body and warmth of tone when I hear live acoustic instruments(they are`nt lean nor lacking color-tone saturation).Depending on speakers,room acoustics and other components the Atmasphere could be ideal.

Given the nature of your speaker I suspect a fuller bodied SET could mate well with such a revealing and transparent speaker(just a guess). Obviously there`s no better solution than to hear both in your system.The good SET amplifiers as has been stated before, are also very transparent,nuanced and also 'fast'.Hard to predict which one a listener may prefer.
Regards,

Spirit,

To answer your questions directed to me:

I had OTL amps for a long time (pre-Zu) and I did listen to an Atmasphere amp on my 1st-gen Definitions before buying Audion Black Shadows. At the time I was using Audiax 88 monoblocks. OTL amps are highly transparent but if push-pull, they still sound like push-pull amps with that subtle crossover notch grunge. You only really notice this once you live with the unity of fast, transparent SET like Audion, and then try to go back to push-pull.

With Zu you don't have to. You have the efficiency for 25w to sound robust and with 845, you get quality bass with the rest of its convincing tone. Other than what someone qualified might homebuild, the synergy between Zu and Audion SET, and a few other similarly-voiced alternatives, is elevating to both.

As I've written before, once you have a Zu speaker the fulcrum of fidelity for your system is the power amplification. It's worth getting right before pouring more money into sources and cables, especially if you have credible bits there already.

Sonically I put the Berning ZOTL scheme ahead of Atmasphere. However, if you feel truly satisfied with your Hovland combination, build on that. I think Black Shadows with proper tubes, into your Defs, will alter your perception of what's satisfying.

Phil