Anyone listen to Zu Audio's Definition Mk3?

The Hovland combination is excellent by any measure. As I've written before, despite the high efficiency, Zu speakers, especially Definitions, make good use of moderate to high power. The main issue to consider is that at 125w/ch, you are running a push-pull tube amp. There's a subtle grunge in the push-pull crossover signal handoff that is absent in SET, and which isn't especially noticeable until you experience its absence. An even excellent push-pull tube amp sounds slightly blurred and congested to me, after years of listening to big-glass SET. On the other hand, push-pull tube amps usually have better bass control and sound (and measure as) more strictly linear, all other things being executed to an equal standard. What is surprising to many who hear it for the first time, is how an 845 SET amp rated for 25w can sound equally or sometimes more dynamic than a 100+w push-pull tube amplifier, on a bursty, revealing and efficient speaker like Definitions.

You have to experience at length SET amplification to understand how it fits your perception of convincing musical sound. A Zu speaker is the perfect speaker to explore this with, and there is perfect concept continuity in mating a single-ended tube amp with a crossoverless loudspeaker. Just don't do it with an old-school slow and sweet kind of SET. At the expense level you're already playing, you can afford a good, objective SET choice. There's no reason you can't mate your excellent Hovland preamp to a good SET amplifier, so no need to take depreciation loss on two pieces if you decide to try the SET power amp route.

The Berning OTL option is also highly credible musically and convincing. Going transformerless but retaining the push-pull topology gives you some of the immediacy of SET but not quite the same thing. Berning has a truly clever OTL circuit that uses an RF carrier signal through a high frequency transofrmer to handle impedance matching without the audio-compromizing effects of an audio frequency transformer. The Berning gear, including the ZOTL preamp, have a specific brand sonic character, which is fast, dynamic and highly transparent. Some people hear it as accurate, others as a little sterile and lacking full tonal body. It's undeniably good. But so is your preamp mated to a suitable SET amp, which if selected well will give you a more holistic, toneful presentation with lots of body. It costs more to get the speed and sheer openness of the Berning in an SET design that delivers the full holistic sound that topology is capable of. Choices.

I think in many respects, the Berning sound can also be closely acquired in solid state in the form of Lavardin.

Phil

My Definition 4s are painted in a high-gloss 2011/12 Cadillac color, Opulent Blue Metallic, with the exposed aluminum parts natural. My Druids are gloss Ferrari red. My first Definition 1.5s were gloss Maserati Blue Nettuno (this became a standard Zu color after I had the first pair built in that finish). My Def2s were high gloss Ferrari red. I use my speakers for 2 ch music and incorporate a 60" display, so for movies the systems are HT 2.0. I don't find the gloss finishes distracting for movie viewing, but then again I manage to ignore incandescent 845 tubes when watching movies so any reflections off the speakers' finish is barely noticeable by comparison. Day to day maintenance is only needed if you have a household of folks who can't keep their hands off the speakers. The gloss finishes are automotive paints that are taking much less punishment than is incurred by a car out in the weather and sun. A little Mequiar's or Mother's instant clean and shine, with a clean microfiber cloth makes quick work of it. But no question the matte finishes require even less attantion.

There are a couple of things to keep in mind about the upper frequencies integration on Def4. First, you're hearing the main full range drivers up to about 12kHz, compared to a two or three-way speaker where the tweeter is crossing in anywhere from 2.5kHz - 4kHz. So most of what you perceive as high frequency performance is determined by the FRD. The new nano drivers are lighter, stronger, faster and therefore more articulate, energetic and refined than the Def2 pre-HO drivers. The spesaker's horizontal spray is also wider than before and most of the Swiss cheese effects in the Def2 soundstage are filled in. That includes the top sparkle frequencies where the Radian plays. Compared to the Def2 FRD/supertweeter hand-off, which was very good at the time of introduction and nothing to be ashamed of today, the Def4 same interface is seamless spatially, tonally and in transient character, and instead of the FRD outpacing the supertweeter as in Def2, in this case if there's preference in sheer beauty at the hand-off, it's in favor of the Radian. This is a lovely tweeter used in supertweeter application here, far better than the ribbons that annoy me, and vastly more listenable than the various and horrid metal and diamond tweeters used in some of high-end's mega-brands. The Radian uses an aluminum dome but with a mylar surround, which avoids the peakiness of most metal dome tweeters. It's not just a claim -- you can hear its extended and smooth neutrality, with dispersion more closely matched to the new FRD than in Def2.

Sidebar: 35 years ago, the Advent Loudspeaker was a great basis for building a highly credible high end system, in a market with much less choice, especially if you had the space for the Double Advent system Absolute Sound helped to popularize. That speaker produced very little worth hearing above 13kHz in a simple 2-way configuration, and spec'd out to perhaps 18kHz. At that time, Jon Dahlquist included a piezo supertweeter on his DQ10, which was flat out to 25kHz, but it beamed like a lighthouse. People did all sorts of things to improve it: wool diffusers over the piezo; replace it with a ribbon tweeter; remove it. Some people just said "....I'll keep my Advents" because they had a rightness to them without the distraction of DQ10's beaming supertweeter.

Well, listen to a Def4, or a Def2 for that matter and have two people handy to put their palms over the supertweeters while you play music. You're hearing nearly the top end of an Advent loudspeaker from the FRD's upper limit. Most of the character of the top end is determined by what you're hearing there. What any Definition's supertweeter adds is harmonic completion, further spatial cues and the subtleties of dfferentiation in expression via instrument materials, playing techniques, vocal inflection and tone. None of the Definitions added this with any ice-pick elements. The cabinet on Def1.5 was a bigger contributor to glare at high volumes than was the supertweeter. In Def2, the top end smoothed out some, but if you needed proof how much more influential the FRD is, you only had to upgrade your Def2s to the 2010 HO drivers. That put the supertweeter's relative contribution in perspective. In Def4 the Radian is a mister instead of a hose with a nozzle. But it's the new nano FRD that sets the stage for you to appreciate the Radian's deftness, dexterity and refinement.

Phil

213Cobra, I really can't thank you enough for such detailed answers which are giving me (and others) a real handle on the identity of the 4s. This is really important since I am likely to buy without audition first; no risk really, since I've been a convert to the tone dense xoverless FRD Zu sound for 5 years now, but your input is invaluable, and lucky for Sean at Zu, decisive!
Thanks for your perspective on amps. I'll be running with the Hovland combination to start, but am v.open to going down the SET route, which I'm fully aware is perfect in a match with 100+dB eff, and xoverless, spkrs.
My choice, since variety in the UK for audition being pretty limited, is to go down the more radical David Berning VTOL 30W/ch SET pre/pow, and on more traditional route Audion Black Shadow 845 SET 25W/ch, either mated to my Hovland HP200 tube pre or perhaps a TVC preamp (Audion dealer in UK recommends Silvercore or Music First). Any experience of the Black Shadow and also TVC preamps in general, which I know can swap overall fireworks for a more subtle rendering of tone and colour?
Just referring to a previous query, my current SS pow doesn't require me ever to turn the volume up past under halfway, hence I'm not using the second half of the preamps available gain. All things on the quality front being equal, will a lower powered SET amp mean that I'll go inro the second half of the preamps available volune setting, and as such will I get more performance from the pre/spkrs?

The Berning 30/30w ZOTL amp has a push-pull output topology, using two of the 33JV6 tubes per channel. They are not, as I understand the circuit, wired PSET. It nevertheless is a clear and highly resolving amp.

Regarding the question of TVC: I headed down the TVC route in lieu of an active preamp about five years ago after I sold my crossover-based speakers and migrated both my systems to Zu. At the time I got the Django TVC assembled by DIYhifisupply, in the S&B TX-102 transformers option, with all internal wiring in silver/teflon. Shortly after that, the US importer shom I've known for over 30 years, was in California and stopped by with his first Music First sample and we compared them. Music First, the integrated products arm of S&B, calimed then that their own version of the TX-102 was in some unexplained way premium to the version they were then selling to other TVC makers, and as I understand it today, a Music First product is the only way a hifi consumer can buy a TX-102 based TVC new.

Regardless, the S&B xformers were and are among the best, and TX-102s including in Bent Audio, DIYhififsupply and other vendors' products were unconditionally excellent. The Music First TVC (what is now their "Classic") was very marginally, just perceptibly more resolving than the Django. It was a very small difference. And some of it could have been due to the Django's steel chassis against the Music First's aluminum. Switchgear, internal wiring and workmanship were fully competitive between the two, despite the considerable price difference (UK-made Music First more expensive).

At the time I had a variety of amplifiers and four active preamps on hand for comparison, three tube-based, and one the Audiopax solid state preamp on loan.

I liked the TVC, and still have the Django as my spare preamp. But it did not win out over my Audion Premier, nor my Klimo Merlino Gold, nor a Melody P1688 I was evaluating at the time. It did win out over my nearly 40 years old Stax SRA-3s tube preamp/headphone amp. I'll say more specifically that the TVCs -- neither of them -- were preferred to the active preamps with my Audion amps, which was interesting because of all the amps I had on hand at the time, the Audions had the highest input sensitivity, so even the +6db gain available wasn't needed.

The TVC did yield several sonic advantages driving Audiopax 88 tube monoblocks, and a pair of Quad IIs. Unfortunately, the input sensitivity on the Audiopax was very low, so the TVC couldn't drive them to full power with normal sources. At the time, to live with the TVC and the Audiopaxes for an extended period and drive them to full dynamic range with a TVC, I had a set of interstage xformers made from S&B TX103 step-ups, so that I could add another 6db of gain. Of course I had to be precise about impedance matching, but it worked with the Audiopaxes. On the Quad II, which have input sensitivity of 1.4v, I did very much like the refined presentation of the Django and Music First, and it has seemed to work well when anyone has brought a solid state amp to listen to.

So, on TVCs, I say your sound quality experiences will vary by power amplifiers. Into Audion Black Shadows and Audion Golden Dreams, the TVC sound is inferior to my tube-circuit active preamps, though I wish it were otherwise because the isolation and lack of an additional power supply definitely makes it easier to chase more noise out of an SET-based system.

Now, Spiritofmusic, on to your volume control range question. I get asked about this alot, so it bears explanation.

Your usable volume control range is not very much affected by the output power of your amplifier. Yes, with two power amps of same input sensitivity, the more powerful amp will deliver somewhat more power at a given volume control level. What you really need to pay attention to is the gain relationship between the preamp and power amp, and/or the input sensitivity of the power amp relative to the preamp's gain and therefore output.

For example: My Audion tube amps have input sensitivity of 0.7v, meaning a signal of 7/10ths of a volt will drive them to full power. Compare this to American amps that generally have an input sensitivity in the 1.5v - 2.0v range. You can see that, depending on the contour of a preamp's volume control and your sources, that generally if I use a power amp with 2.0v input sensitivity, I would get much more usable rotational range on my preamp's volume control. In fact I hint at this scenario in the discussion above. With a disc player having the standard 2v output, connected to a 0db gain TVC where all you can do is attenuate, I could not drive the Audiopax 88 amps to full power even with the TVC volume control turned all the way up, because the Audiopax's input sensitivity was greater than 2v. In a market where most power amps have 24 - 32 db of gain, the Audiopax 88 has only 18 db gain. On the other hand, the TVC set for 0db gain could easily drive the 0.7v input sensitivity Audion amps to full power with the attenuated output of a 2v out disc player.

So what to do when you use an active preamp? This is where input level control on power amps are helpful, because most gear has too much total gain in the chain. Right now, two of my three active preamps are fairly high gain -- the Klimo is 20db and the Melody 101 has 23 and 15 db options. But they each sound great with the Audions. The advantage is, my preamps are quieter than are my SET power amps (common for SET). So I can prioritize the gain in my quiet preamps over the gain in my noisier power amps by running the input level controls turned very low, effectively raising the input sensitivity by "throwing away gain" at the input level pot. This way, I get more usable rotation in my preamp volume control, and lower the system noise floor by reducing SET noise. It's not an amp power issue. I could put in an pair of 1200w McIntosh monoblocks with ~2v input sensitivity and have more volume control range than I'd have if my Audion amps didn't have input level controls, though there could be bigger consequences if the volume control were set too high. The point is, regardless of the power amp, you can choose a preamp/power amp combination that molds the gain relationship between pre/pwr to your operating advantage.

If the gain relationship or output/input sensitivity are not mated well, you won't get more useful rotational range from your volume control with a lower powered amp, but you might push the amp into clipping sooner. Make sense to you?

So if you want more usable range out of your preamp volume control with a given power amp, you either have to choose a preamp option with less gain or need a way to throw away excess gain via input level controls or find lower-output sources to eliminate the problem. A TVC gives you a 0db gain option or at most +6db optional, to reduce system gain, so if it in fact sounds as good or better than a higher gain active preamp, you will get what you're seeking irrespective of the power amp's output.

Phil

213Cobra, you come to the rescue of us poor, non-technical souls out here! I do love the sound of my Def2s thru the Hovland combination, and if this is continued into the Def4s I won't be in a hurry to switch amps. Handy really, since giving my cash to Zu won't allow me to for the time being anyway!
So I gather from your answer, if I'm not mistaken, is that I don't have to chase possibility of using full range of preamp's volume control to acquire more dynamic control over sound if I'm happy with sound with preamp never beyond half way up as it is anyway.
Reading between the lines, the Berning amp combination, to your ears, is leaner tonally and faster dynamically than the Audion 845 SET, and the latter is where your musical happiness lies. That is warmth and tonality win over detail and speed, given the choice between highlights in these amps' signature attributes.
Luckily in the UK I'll be able to get a home demo of Audion Black Shadow and matching pre, and Berning pre/pow combination to make a clearer decision (if ever get to that stage).
Just getting back to the Def4s, since this thread is about them, can you go into any discussion re their stiffer structure: I gather quite a bit more metalwork has been applied esp. in the plinth for the sub bass and also the front panel for the FRD's/supertweeter which has increased weight 50% and contributes a lot to controlling cabinet resonances.