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Decware Zen SE84UFO

Discussion in 'audio' started by Tony L, Feb 7, 2016.

  1. Tony L

    Tony L Administrator

    Anyone here heard the recent UFO transformer update/upgrade to the little 2.3 watt Decware Zen SET? I have a distinct itch to buy one for my Klipsch La Scalas.

    I tried a pfm member's Zen a while back and really liked what it did and I think I could justify running such a small tube amp even though this is the TV/background system and is usually on for many hours a day. Rectifier aside it uses cheap and easily available tubes (long-lasting Russian military 6P15P-EV output tubes), and being so tiny and feeble in output I can't imagine it spinning the electric meter too fast, i.e. it shouldn't be too costly/wasteful.

    My La Scalas have after-market ALK Universal crossovers which are apparently a constant 8 Ohm impedance, so given the crazy high efficiency (105db) these speakers should technically be as good a match for a flea-powered SET as is possible. I typically listen at around 75-80db, so I doubt I've ever flung a quarter of a watt into them yet! As I have these crazy speakers it just seems wrong to use them with a solid state amp (I'm using a Quad 306) when it is widely acknowledged that they really do not give their best with such things. I certainly liked the Zen I tried with them so it wouldn't be a completely blind punt. I'm just curious as to what the current update brings.
     
  2. Rana

    Rana pfm Member

    Indeed. Would also love to hear Decware tubes with my Decware ERRs. The only valves I've used with them was an Easter Electric Minimax, but they had to go as my little boy (then still quite young) showed too much of an interest.
     
  3. Paul R

    Paul R pfm Member

    Amplifiers shouldn't be called 'Decware', it just makes me think 'museum of computing'.

    Spec says 65W, so grossly inefficient but not an absolute issue. If your speakers really are that efficient then there's an implied possibility that the amp may be a bit noisy. But if you've used one and were happy then why not?

    I'd be interested to see how something like http://twistedpearaudio.com/linestages/ventus.aspx sounded. I think 0.5W only, but it should be about a perfect 0.5W.

    Paul
     
  4. Tony L

    Tony L Administrator

    Museum computing is a weekly hobby, so no issue there, in fact one of the guys on my day's team is ex-DEC! I hadn't spotted the 65w, that's fine, I can certainly live with that. Probably only about twice that of the Quad, which I tend to turn on when I get up and off if I go out or know I'll be spinning records in the other room for hours. I'd be a lot more frugal with a tube amp so it would likely work out the same.

    The thing with the Klipsch is they are a vintage design (1963 in the case of the La Scala) and date from a time where there was no "perfect amp", they can sound hopelessly dry and lean with modern tight solid state amps, plus if there is any grain or noise anywhere they'll find it.

    The Zen I tried was surprisingly quiet, a little mechanical transformer buzz though nothing of note through the La Scalas, I have heard some say their sample hummed though, which is a little worrying. I guess a lot depends on the specific tube set, e.g. I can convert my normally quiet Leak Stereo 20 into a white noise generator by sticking a crap ECC83 in the input gain position and I guess quality of the rectifier tube impacts hum. I'm pretty sure I'll end up buying one as it just seems daft owning such rare and odd speakers and not playing to their strengths.

    I've been reading the Decware forum and get the impression that the stepped attenuator actually has more usable volume range (i.e. gets loud further round), so I'll likely go for that option. Do I want copper in my beeswax caps, that is the next question...
     
  5. 786

    786 Another day, another box!

    About 4 years ago, I imported two Decware Zen Triode kits from Steve Deckert with all components and transformers to Decware specs for UK supplies. I bought custom Italian cases and had a well known professional Hifi supplier assemble everything for me, using pure silver wire, audio note ancillaries and various special customisations. The best decision I made was to have each amplifier assembled as a mono bloc, which Steve Deckert provides for in his instructions on building the Zen, so each 3 watt became a 5 watt SET and stable down to a 1ohm load. The cherry on the cake, my best decision, was to include in each mono bloc a high quality volume/gain control totally negating the need for a preamplifier. By giving each mono bloc its own volume control, I have had the amazing opportunity to connect my source (SACD, TT etc) directly to an amplifier with a circuit with just 3 components in the signal path. If you connect to a full range speaker (without crossover) you have the purest sound experience I have had the pleasure of listening to. I highly recommend the Zen triodes for uncanny listening experiences with high sensitivity speakers, if you get the chance definitely buy a Decware amplifier they are amazing.
     
  6. paskinn

    paskinn pfm Member

    I have not experience of the Decaware, but i have regularly used low powered single ended amps (2a3) to drive my 95db speakers...about 3 watts all out. The sound is very fine.
    However are you already using your Leak 20? If not, give that a try. I now use a pair of Quad 11s rather than my SET because the bass is better with no loss of overall quality. You could always wire the Leak in triode, there would still be plenty of power. Simplicity of design seems to be the key, rather than a single-ended circuit in itself.
     
  7. G T Audio

    G T Audio Trade: Manufacturer and Distributor

    The dilemma is not whether the Decware will drive your Klipsch La Scalas - it will. It is about the amplifiers ability to control that 15" driver, especially at normal, and higher listening levels.

    Low power SETs (also triode wired pentodes) have a high output impedance and a poor damping factor, meaning the large 15" driver will not be well controlled. I wouldn't even think of anything less than 8 watts unless you are driving a speaker like the Arcadian Pnoe horns with a single 4" inch full range driver. The best way to "SET" drive the La Scalas is with a 211 or 845 based amplifier running with a high HT voltage. The higher drive capability does a much better job of controlling that big cone but even then feedback would improve drivability even further, but then why bother with a SET in the first place? I would have thought your Stereo 20 would have been the perfect amp, having 12 watts and a good dose of feedback for perfect control of that large cone...
     
  8. Tony L

    Tony L Administrator

    All points above are very valid. I'll try and better explain my reasoning for going for a Decware (which I have now ordered).

    Firstly this is my TV/"pfm office" rig. It is on for background use much of the day. It really is not practical to use a 'proper' sized tube amp here as I'd be burning through expensive tubes and spinning the electric meter way too fast. Even the Leak would be impractical to run, let alone something using 300Bs, 845s or whatever. The Decware uses 65w flat out and the Russian 6p15p-EB output tubes are thankfully extraordinarily cheap and long-life, as is the input tube. It can even use cheapish rectifiers. As far as a proper tube amp goes this is as 'green' as it gets.

    Secondly I have actually tried a SE84 and like the way it drives my La Scalas. It may not be the best thing one can throw at a La Scala in the grand scheme if things, but in the context of my intended usage it is probably the only tube amp that is actually feasible! I felt the one I tried gave a rather bigger, warmer and more open sound than the modified Quad 303 I was using, so I suspect I'll enjoy it.

    [​IMG]

    It is also worth noting that I'm using the fancy third-party ALK Universal crossovers which apparently present a pretty constant 8 Ohm load to the amp, i.e. the little SET does not need to deal with the high-impedance mid-horn swing of the original design.
     
  9. paskinn

    paskinn pfm Member

    Why is it the only 'affordable ' option? You mention the extra warmth you are seeking, well, that's something you can get from the Quad 11s. They will grip the bass better, be more in keeping with the vintage ethos and give you something to renovate during quiet evenings.
    I note the crossover. Even with a steady 8ohn (good!) it will suck life from a little SET amp. I've been taken aback by how much power a crossover consumes.
    Here I could go into my 'single, full(ish) range drivers with no crossover do least harm' mode, but I'l take pity on you all.
     
  10. Martin J

    Martin J pfm Member

    Tony,

    I will be interested to read about your Zen in due course. Mine is still doing sterling service with your old Heresys and a Naim Dac V1 in our flat. It's a great second system.

    I stuck with the Sovtek output tubes that you recommended but use the original input and rectifier tubes.

    What's the lead time like these days?

    Martin
     
  11. Tony L

    Tony L Administrator

    Have you seen the price of even half decent KT66s?! Don't even start me on GZ32s!

    Remember the La Scalas are 105db efficient, which IIRC is a good 5-10db hotter than your Voigt single drivers. 2 watts into these will generate 108db! That is pretty much rock PA volume! With this system I listen at an average of 70-75db, so I'm never going to be out of the milliwatt range. Resorting to basic loudspeaker maths to make my point: driving La Scalas with 2 Watts is the direct equivalent of driving a 85db pair of speakers with a 260 watt amp! (each 3db equates to a doubling of power, and I've not even added in the extra 3db gain of having two speakers in a room, i.e. I'm actually good to 111db!). Even so I'd be a little worried if I hadn't already tried it and have a good idea what to expect. I'd not have taken a leap in the dark. The only difference is the current model apparently has better output transformers, and that is seldom a bad thing!
     
  12. Tony L

    Tony L Administrator

    Finally turned up today, delay not Decware's fault, just hopeless import/customs process in the UK that took from the 26th May until today to get through the bureaucratic processes.

    [​IMG]

    Initial impressions are it sounds very decent from first switch-on, but I'll get used to it for a month or so before really commenting. It goes plenty loud into the La Scalas, volume knob position in picture representing a typical listening level and apparently the whole range is useable assuming a 2v input (it's a gradual curve, but 12 o'clock is far more than I'd ever want to be in the room with a typical CD). It hums just a little on the 'switch forward' forward input tube bias setting and rather a lot on the 'back' one, which is a shame as I suspect I may prefer that one (La Scalas really will find hum or hiss in absolutely anything, and the lower bias setting is no worse than the beautifully quiet Quad 306 I was using previously). Hiss is a total non-issue, I can't hear any. It has two impedance settings selectable via switches on the output transformers, though like the input tube bias setting they are not labelled, one is 4 Ohms, the other 8 Ohms, though I have no idea which is which. I prefer 'switches forward'! It really is nicely made, I had a quick peep inside before powering it up just to make sure nothing had come loose in transit. All hard-wired and with very nice components. I went for the audiophool copper in beeswax caps just for the hell of it, but the rest looks very decent too. Will report back once it has burnt-in for a week or two and I've really got a handle on it.

    PS I may well end up sticking spades on the speaker cables so they don't stick up in the air!
     
  13. Rana

    Rana pfm Member

    Nice one, Tony. I eventually went the way of a Unison Preludio for my Decware speakers, as it was about the same price after import and taxes. Happy for now.
     
  14. TimF

    TimF pfm Member

    Congrats Tony, glad the little beast finally showed up! Will be interested in your thoughts on it as time goes along.
     
  15. Hoopsontoast

    Hoopsontoast pfm Member

    Very Nice Tony! :)

    I keep thinking about getting my Zen out but its finding a balance for the speakers, that are efficient enough and will work in my room.

    I tried Hereseys but I just did not get on with them at all, not my taste.
     
  16. Tony L

    Tony L Administrator

    Klipsch are odd things, I've no idea if I like them myself to be honest. They are astonishing in some respects, but hopelessly coloured in others. I'm convinced there is a truly spectacular speaker in the La Scala somewhere, in some ways the best I have ever heard, but it would involve a lot of destructive DIY to unleash fully (e.g. the cabs really need bracing/damping), and I'm not prepared nor capable of embarking on that path. I suspect I'll just enjoy them for what they are as long as I have a dedicated TV rig in a largish room, then bounce them out for something different.

    I've been very impressed with the DIY Frugal Horns I've heard, I bet with the right (i.e. efficient) driver choice and without excessive volume expectations they'd be a great match. I like the idea of trying a full-range driver speaker at some point down the road and I get the impression some modern designs (Fostex, Mark Audio etc) are very good indeed.
     
  17. John

    John Rack’em Up!

    Same here, had a nice used pair back in the early 80's.
     
  18. fleapower

    fleapower Member

    Tony, I'm surprised that you don't find the combination of the Zen with the LSs to be outstanding. I've worked with many guys using the latter in relatively small rooms, and low power SETs and SEPs are almost magical. I think you mentioned using Klappenberger's constant impedance crossovers. Do you still have the original Klipsch crossovers to swap back in? It would be a very worthwhile experiment since SETs are fairly immune to the normal impedance variations across the audio band.
     
  19. Tony L

    Tony L Administrator

    I missed this yesterday. Don't get me wrong, it is sounding very good, in fact better today now I've swapped the supplied Chinese 5U4 rectifier out for a nice NOS Mazda 5Y3GB. That made a big difference and has lost the hum to the point both input tube bias settings now sound fine. I also bought a black plate Sylvania 5U4GB and that sounds great too (both from Watford Valves). Chinese rectifiers have a reputation for being crap, which seems deserved, so I was surprised to see one there to be honest. The other tubes are decent commie-era Russian, so fine. I've ordered some more from eBay so I've got a stash for the future.

    I do have the stock crossovers and I will one day recap them and give them another go. I know I very much preferred the ALK Universals when I first got them, though I was running a solid state amp at that point (Quad 303). I definitely like the little Zen, it is a very good little amp IMO. I'll report back more once I've better hot to know it.
     

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