[jsm71]

I just brought home my new Decware Zen Mystery Amp (ZMA), Steve Deckert's latest new model.  I'll put an explanation below on the goofy name; there is a story behind this.  Although I just got this and I have many hundreds of hours ahead of me for its break in, I know how it will sound eventually.  This model was on display last fall at Steve's annual "Decfest" at his place before it was available to anyone.

This is a very basic (minimal parts) push-pull class A (only) design that uses zero negative feedback.  Output is 40 watts/channel and not over driven for longer tube life.  It is a true dual mono design on a shared chassis.  Only the power switch and cord are shared.  The beauty of the design is with the power supply.  It is way over supplied and those big caps have some real benefits.  As with all Decware amps no circuit boards are used, only point to point wiring. In this model high end parts are used as well, including cryoed flat stacked Jupiter signal caps.  The big red caps on my model are NOS Mallory caps, an upgrade over the stock (black) caps.  I kind of like the looks, some probably hate it.  The big caps hold incredible stock reserve which really smooths out the sound and holds all you need for great dynamics.  Because of their size no chokes were needed, another simplifying element.  A couple of early buyers claim they tried various power cords and were able to swap them in an out while music was playing, never missing a beat.  I haven't tried that.

The ZMA comes shipped with KT66 output tubes, but EL34, 6CA7, KT77, KT66, 7027, or 5881 can be used.  Input tubes are 6N23P, but 6922 or 6N1P can be used.  NOS OA3 voltage regulators finish out the tube display.  Tube biasing is required but couldn't be simpler.  All four output tubes have their own biasing supply and measurement meter.  The biasing is done as a channel.  Each channel has a dial hidden behind the regulators which brings both channel tubes up to the desired voltage.  A second and easier to reach turn control balances the two channel tubes to be equal.  Done, without tools and can be adjusted on the fly.

The sound of this amp is best described as very liquid but with no lushness.  Some Decware amps have that wet lushness that many tube lovers love.  This is all business no doubt a result of the power supply and per Steve's design comments strives to achieve what his top of the line mono blocks provide at a much lower cost.  Initial cost today is set at $4,695.  A few options including an additional set of balanced inputs, the Mallory caps, a stepped volume control, and wood base options can bring that price up.  I expect the price will rise about $1k once the initial buying wave is over.  Steve did similar price hikes with other models once initial user testing qualified the amp's readiness.  I waited about 12 weeks for mine to be built, typical for doing business with Decware but well worth the wait.


Note:  The name "Mystery" amp came from early teasing from Steve on his forums where he showed build in progress pictures without telling anyone what he was building.  This mystery design was eventually tagged the Mystery Amp and the name stuck.
 

[JakeJ]

Suh-weeeet!  Congrats, jsm71.  Keep us posted as to how the sound changes and the attributes you like best over amps you've owned in the past.

JakeJ

[bladesmith]

Looks sweet, with many tube options, even sweeter.

(The 6n23p's will not be disappointing. )

[doorman]

Having owned several Decware amps, " wet- lushness " wouldn't have applied to any of them, but who knows.
Your ZMA is a killer unit, so versatile, power to drive most speakers with authority, and superb musicality.
Happy listening.

[planet10]

Output is 40 watts/channel and not over driven for longer tube life...
The ZMA comes shipped with KT66 output tubes, but EL34, 6CA7, KT77, KT66, 7027, or 5881 can be used.

None of those tubes are capable of 40 W in Class A PP.

If run in triode more like 10W/channel. If run in Pentode about twice that and a current amp -- that is cool, but would give strange results with most speakers since a voltage amp is assumed by the speaker designer.

dave

[bladesmith]

The web site says 40 watts, weird.

Bladesmith

[planet10]

The web site says 40 watts

Steve has often beem caught with colourful prose that is suspect.

We ran across similr with the "45w class A no feedback" KT88 Grant Fidelity RITA we have in-house. It has a feedback loop, and the most we could get out of it Class A was about 20W but it sounded best at 35 w Class AB.

A pair of any of the tubes listed are physically incapable of 40W Class A.

dave

[bladesmith]

Is your research based on product comparison or on engineering principles ?

Bladesmith



 

[planet10]

Is your research based on product comparison or on engineering principles ?

Both.

Althou there are  many UL Class A PP No NFB amps to compare.t
Tube data says 9.5w anode power dissipation per tube with 390V across the tube

http://tdsl.duncanamps.com/pdf/kt66.pdf

dave

[jsm71]

Steve's specs are actually 38 watt/ch run Ultra-linear but he markets them as 40 watt class A dual mono amps.  I'm no engineer.  The performance specs and design features are taken from Steve's web site.  I do have anecdotal experience that suggests the numbers are believable. 

My speakers are JansZen zA2.1s, hybrid ESLs.  They carry a 87dB sensitivity rating.  Before I got the ZMA I had Decware's Torii MK IV rated at 25 watts/ch.  The Torii was driving the JansZens quite well with amazing bass although it would give out before the speakers would.  I don't listen at rock concert levels any more and the Torii was great.  I stepped up to the ZMA becuase I may have a larger listening room some day and I felt the almost double power would be useful.

I haven't pushed the ZMA to see how loud it will play, but I can feel the extra power in dynamics and tighter bass over the Torii even though it is still early.  Just based on the modest sensitivity of my speakers and the support this amp gives them I believe 40 watts/ch can't be too wrong.  I can also attest to the transparency being very close in sound to his other SET amps.  The overall sound still has some edge to it which will shave off as it breaks in.  In the end I know it works as expected and it's sound will be hard to top in its price range.

[Ericus Rex]

Everyone's confusing push-pull with single ended.  Class A PP is still push-pull and not single ended.

[planet10]

Everyone's confusing push-pull with single ended.  Class A PP is still push-pull and not single ended.

Not me. PP Class A & PSE will have the samepotential output power.

dave

[jsm71]

I said, "I can also attest to the transparency being very close in sound to his other SET amps."  Strike the word other.  I fully know that this PP pentode amp is not a SET amp.  The big caps just filter the power feed so much the transparency is wonderful.   

[FullRangeMan]

None of those tubes are capable of 40 W in Class A PP.

If run in triode more like 10W/channel. If run in Pentode about twice that and a current amp -- that is cool, but would give strange results with most speakers since a voltage amp is assumed by the speaker designer.

dave

It would be 40W of plate dissipation, not output watts.

[FullRangeMan]

Everyone's confusing push-pull with single ended.  Class A PP is still push-pull and not single ended.

Not sure why referring PP as Class A, it looks Class B to me, since it use a phase splitter and two tubes at output.
SE and PSE are Class A.

[planet10]

It would be 40W of plate dissipation, not output watts.

across all 4 tubes...

dave

[planet10]

Not sure why referring PP as Class A, it looks Class B to me, since it use a phase splitter and two tubes at output.
SE and PSE are Class A.

Depends on where the bias is set. If a PP amp is Class A all the tubes need to be fully on all the time, in Class AB a tube turns off for part of the cycle, One of our best amps is a trioded Class A EL84. It outputs 3.2 W at clipping.

dave

[Guy 13]

Depends on where the bias is set. If a PP amp is Class A all the tubes need to be fully on all the time, in Class AB a tube turns off for part of the cycle, One of our best amps is a trioded Class A EL84. It outputs 3.2 W at clipping.

dave

Hi Dave.
Any picture(s) of your best triode Class A el84 ?
Or a link where I can have a look.

Guy 13

[FullRangeMan]

Depends on where the bias is set. If a PP amp is Class A all the tubes need to be fully on all the time, in Class AB a tube turns off for part of the cycle, One of our best amps is a trioded Class A EL84. It outputs 3.2 W at clipping.

dave

Thanks for mention this detail I was unknow it.

[planet10]

Any picture(s) of your best triode Class A el84 ?

It never got pretty (have to build another one 1st) It is an El-Cheapo derivative.



dave