Anyone listen to Zu Audio's Definition Mk3?

Excellent choice Gopher. :)

Thanks Glory.

Phil, when I receive my Def4s I'm going to install them with my current Hovland HP200 tube pre/Radia SS pow amps.
Luckily in the UK I will have the opportunity to audition Audion Black Shadows SET pow/Audion tube pre (or Silvercore TVC pre), Dave Berning VOTL 230 pre/pow and ASR 4 box amps.
My new tt is unbelievably fast, a function of it's neutrality, lack of overhang and superior timing, and I have my eyes (ears?) on a very fast, analogue like cd player. From what I've read, the Def4s have a very fast delay of 5ms betwen the drivers, as opposed to the usual 20ms (a function of no crossover maybe?) contributing to maximum speed.
This preamble is to state that speed and neutrality are becoming the benchmarks for me.
I know the ASR, and esp. the Berning combination of amps are v. fast, and I gather you feel the Audion Black Shadow is just as fast as these choices. Am I correct in this? The reason I ask is that I've never heard an all tube pre/pow combination that I was totally content with in this respect, but with your encouragement, maybe I should consider Audion.

Spirit,

The ASR sounds neither notably "fast" nor "slow" so I don't think speed in a hifi sense is a notable trait for that amp. I'll say it's "fast enough." Given where you are starting (Hovland/Hovland) the ASR will probably strike you as the least interesting in this particular respect. The Hovland 200 preamp was intentionally voiced to sound completely modern, compared to the more vintage-voiced 100, and as a result it's a "fast" tube preamp and the Radia won't disappoint in that respect.

Audion circuits are simple and sound characteristically speedy -- more so that any tube products I can think of. The Audion preamps are beautifully toneful yet neutral and transparent but for now they lack remote controls. The power amps, regardless of SE or P-P or power level or tubes used carry these traits forward. You can "slow" them a bit by choosing tubes accordingly but there's no reason to strive for an explicitly slower sound specifically. Black Shadow has silver in the signal path wiring and silver secondary transformer windings. Cap and resistor selections make their contributions. A Silvercore TVC is also likely to be a good front end for it. Berning amps have also always been notable for speed, transparency and tone within their topology. So if you like immediacy and event speed, everything you're planning to audition with Def4s qualify. You'll just have to listen and draw your own conclusions. I expect the ASR will prove the least engaging of the electronics you're considering beyond the Hovland gear you already own. The Berning is its own thing. The Audion combination represents single-ended exceedingly well executed for music. You're getting speakers that will lay bare the differences so you can easily choose.

In the Black Shadows, the 845 tube makes a big difference. The expensive KR845, the inexpensive cryogenically treated 845A, and the metal plate 845C are the "fastest" readily available options. The 845B and the stock 845A are the slower of the bunch but the general circuit execution sounds so fast, the total sound retains exceptional perceived speed. The 845B is reliable and brings exceptional tone -- I want to cryo a pair to pick up the advantages I heard in the chilled 845A. The amps ship with the standard 845A which is fine. There is a Sophia 845TypeIII that I'm optimistic about but haven't yet tried. The input and driver tubes have a significant effect but the stock tubes are certainly very good for audition.

Each of these amps will have differing bass characteristics. When you switch between them, adjust the sub level and EQ to tune the bottom end to a common standard, else you will be apt to draw false conclusions depending on your biases. You could view the Berning as a "midpoint" between the ASR and the Black Shadow but that will leave you with bass perceptions that infect your view of the midrange on the amps that aren't the centerpoint one. I haven't heard any two amps on Def4s so far not require tweaking the sub parametrics when switching between them. Remember the sub amp is deriving its input from the power amp output - not from a line-level signal.

Phil

The Audion and Berning will have to be a significant improvement beyond where my Hovlands are at present to consider upgrading. I remember when I got them in 2005 I was so happy with the excellent synergy between the tube pre and SS pow, and I'm still happy with them now.
I have a strong suspicion that the better bandwidth and transparency of the Def4s esp. lifting the veil from the treble of the Def2s will reveal the Hovland combo to be more excellent than ever.