See the complete review in TONE AUDIO Magazine No.71
- 40 watt dual mono amplifier.
- Optional transformer b alanced XLR Inputs & RCA.
- Input level control makes it possible to use with no preamp.
- Ultra cool bias adjustment - no tools required.
- Large Meters - let you maintain PERFECT tube matching without effort.
- Exotic parts - cost no object design.
- Compatible with a wide range of speakers
- KT66 Ultra-linear output stage is also compatible with other tubes.
- Dual Mono design
- Lifetime warranty
||One of the things that makes the Zen Mystery Amp unique is it's insane power supplies.
A typical tube amplifier this size uses power supply capacitors totaling about 80 micro-farad.
The Mystery Amp has 45 00
micro-farads. Yes, that's about 50 times more than normal but we did
mention that this was a cost no object design and th e massive capacitors
come with some huge sonic benefits. Each amplifier's power supply
has enough stored energy to start your car and melt all four tires to
the garage floor!
In fact, these capacitors are so large that the amplifier sounds as if it's being run on batteries.
Steve Deckert - owner DECWARE High
ZEN MYSTERY AMP
The Zen Mystery Amp's bias system makes sure you
know if your matched tubes really match, let you force them to match
when they don't and keep your tubes from failing prematurely not to
mention sounding their best throughout their entire life cycle.
THE ZMA ADJUSTABLE BIAS SYSTEM
The Zen Mystery Amp features 4
independent bias supplies and 4 precision current meters, one for each
output tube, so that adjusting one has zero affect on the others!
The meters give you a real time view of how each tube is doing and how well they match each other.
A simple balance control between each pair of meters lets you match the tubes at any time while the amplifier is on.
The meters also show you if a tube is going bad and which one - at any power level.
A visual power indicator, the meters begin to dance when the amp reaches maximum output.
True Analog movements in each meter make it
possible to predict tube performance by simply watching the meters
behavior during warm up.
The Mystery Amp came directly from our signature Zen TORII mono-blocks.
We wanted something with similar performance, but in a single chassis
and at a reduced cost. By building two mono amps in a single chassis,
eliminating the fancy transformer covers, reducing the power a bit,
using smaller meters and finally by making balanced XLR inputs optional ~
it was possible to maintain the same cost no object design and internal
parts used in our $12000 mono-blocks.
The Mono-blocks are unique in that they have a massive power supply with
caps so large it is possible to eliminate the choke and any dropping
resistors feeding the output stage. Unless you see an amp with similar
size caps, you can be certain that it has at least one if not both of these current limiting
necessities. This is why the Mono's sound better than almost
everything. Well, on that note, the Mystery Amp explores this zen
approach a little further by doubling the capacitor size and eliminating
the dropping resistor that feeds the input stage. Instead a vacuum
regulator tube was used to drop the voltage with no heat and 20 times
the ripple rejection of the resistor it replaces. This was a personal
goal of mine because it makes this the first tube amp power supply in
the world that doesn't use a choke or any current robbing
resistors to supply both the input and output stages of the amp.
Consequently there is no heat or parts to fail. The real impressive
part however is the liquidity and speed that results from eliminating
This is about as close to pure DC power as you'll ever get in a 500 volt
amplifier. As a result, the Mystery Amp will have about 50 times
the immunity to dirty power from your wall outlet.
The other nice thing about this amplifier is how it handles the output
tube bias adjustments. We've all seen tube amps that have blown up
due to "bias runaway" when the plate inside the tube gets red hot and
causes the tube and sometimes the amp to fail. This happens
because many amplifiers share a bias supply between more than one
tube. Setting the bias wrong, or using mismatched tubes can
trigger this event. It's a big reason people who like cathode
biased amps, like cathode biased amps better than fixed bias amps.
Anyway, an adjustable fixed bias amp can actually be as reliable and
sound as good or better by simply doing it right.
In the Mystery
Amp, I created independent bias supplies for each output tube so that
when you adjust one tube, it does not affect the other tubes. That
way you only ever have to adjust it once, instead of ten times until
you happen to hit it just right. Also a lot of time was spent
defining windows of adjustment that worked with all the recommended
output tubes without allowing the user to get into too much trouble
should he/she miss adjust it. In fact, most of the time it will
impossible to get into trouble ensuring long happy tube life.
biggest thing is output tube matching in push pull
amplifiers for linear
output and max power, so to that effect rather than have a
adjustment for each tube, we have one for the pair and
one as a balance
control located between the meters so that the user can
the meters at any time in less than a second. Each
channel is set up
this way. You'll find this handy since tubes drift with
temperature and this allows you to counter it on the fly
as you listen without tools. It takes all the pain
in the ass out of owning a
fixed bias amplifier. Of course the meters make
great tube testers
and clipping indicators allowing you to see if any one
prematurely clipping relative to the others despite being
matched at idle.
The voicing on this amplifier is more particular than anything I've
done, short of the TORII Mono's. I say that because I have a very
strong preference for the 6N23P input stage as that is the only tube I
like in this amp. Cryo-treated with silver leads, and flat stacked
beeswax film caps are used for all internal coupling, and 2 watt carbon
composition resistors throughout the signal path. Factory Tube
compliment is the Tungsol KT66, and OA3 and for the driver stage a pair
of Russian 6N23P-EV.
Another delightful thing about this amplifier is that is has zero
negative feedback so the imaging and sound stage depth are unrestricted
and capable of rending whatever is on the recording.
In the end, it is every bit the fidelity and performance of the Zen
TORII Mono's with a bit sweeter top end. On most speakers greater
than 86dB there was no noticeable difference in power between the
Mystery Amp and the Mono's.
The OA3 feeding the input stage combined with double the capacitance of
the Mono's gives the Mystery Amp unparalleled accuracy and liquidity.
NOTE: There is also a forum thread on the Mystery Amp that I started early in the design process.
World Voltage compatibility 50/60Hz
INPUT TUBE Compatibility:
6N23P, 6922, 6N1P, 6DJ8, 7DJ8
OUTPUT TUBE Compatibility:
EL34, 6CA7, KT77, KT66, 7027, 5881, 6L6G
INPUTS: OPTIONAL TRANSFORMER BALANCED XLR INPUTS
INPUTS: SINGLE-ENDED RCA INPUT
OUTPUTS: 4 & 8, or 8 & 16 OHM SPEAKERS
IDLE CURRENT: 40~70
MILS PER OUTPUT TUBE - ADJUSTABLE
HIGH B+ VOLTAGE: 410 VDC WITH LOAD
INPUT IMPEDANCE: 100 K OHMS
FULL POWER @ 2.0 VOLTS ON RCA INPUT
POWER INTO 4 , 8 or 16
OHMS: 38 WATTS PER CHANNEL
PRECISION CURRENT METERS 0 to 100 MA
WINDOWED BIAS CONTROL to ADJ OUTPUT TUBES
DYNAMIC BIAS BALANCE CONTROL FOR PERFECT MATCHING of EVEN UNMATCHED TUBES
600V CRYO TREATED COPPER FOIL BEES WAX - SIGNAL CAPACITORS
OPTIONAL 20 POS STEPPED ATTENUATOR w/ GOLD CONTACTS for INPUT LEVEL (GAIN) CONTROL
4400 UF 500V LABORATORY GRADE POWER SUPPLY CAPS
GOLD TEFLON INPUT JACKS
RECTIFICATION: ULTRA FAST RECOVERY 3 AMP 1000V
MACHINED STEEL CHASSIS with POWDER COAT FINISH
HI-GRADE FUSED IEC CONNECTOR for REMOVABLE POWER CORD
SOFT START- NO STANDBY NEEDED
PREMIUM GRADE KT66 OUTPUT TUBES
PREMIUM GRADE 6N1P-EV INPUT TUBES
OA3/VR75 REGULATOR TUBES
19-1/8" WIDE x 13-3/4" DEEP x 8-3/4" HIGH
NET WEIGHT: 43
LIFETIME TO ORIGINAL OWNER / 90 DAYS ON TUBES
carefully hand select and match the tubes for these amplifiers. The
amplifiers are tested and burned-in with the tubes you get.
These include four Russian Military Grade 10,000 hour
6N23P-EV's with gold grids, four KT66's and two OA3's per amplifier.
(Note the amplifier is also compatible with 6N1P / 6922 / 6DJ8 / 7DJ8 as
well as KT77, EL34, 7027, 5881, 6L6)
The ZMA comes with some options.
All of these can be configured from within the shopping cart.
You will be able to select between 110/120 volts
50/60Hz or 220/230/240 volts 50/60 Hz. We will investigate your
countries actual voltage and plug type and wire the amp accordingly.
You can select
from a black figured base OR contemporary styles like the ones shown
below. Along with the option to have one made in custom woods.
When custom woods is selected, a phone call about what wood and what
finish you want will happen.
Base options from top to bottom: Maple, Cherry, Black, Walnut, Black Figured.
OPTION 3 - VOLUME CONTROL
You may select from a normal smooth-action
volume control OR a stepped attenuator if you prefer those. Our
attenuator has 20 steps.
OPTION 4 - KNOBS
Black, Cream, Walnut.
OPTION 5 - OUTPUT TRANSFORMERS
Your amplifier can be configured to use 4 and 8 ohm
loudspeakers, OR it can be configured to use 8 and 16 ohm loudspeakers.
OPTION 6 - INPUTS
The amplifier comes standard with RCA inputs (aka
Single-Ended inputs) but can also be configured with
transformer-balanced XLR inputs. When the amp is configured for XLR
inputs, you will still have RCA inputs and either can be used, but not
both at the same time.
Here are four Anniversary Mods that were developed to narrow the
sonic gap between this and our 25th Anniversary Zen Triode amplifier.
These mods accomplish this by using the same 'cost no object' approach
as was used in that amplifier.
ANNIVERSARY / OPTION 7 - Beeswax Bypass Mod
This option installs matching cryo-treated beeswax signal caps on the plates of each audio tube.
ANNIVERSARY / OPTION 8 - Glass Resistor Mod
This option replaces the signal resistors with
hermetically-sealed glass-cased resistors from NASA. They are military
ANNIVERSARY / OPTION 9 - Nichicon NX Cap Mod
This replaces the two giant electrolytic capacitors used in the ZMA with industrial grade counter parts.
NOTE: All reviews through 2019 of the Zen Mystery Amp have been done without
ZEN MYSTERY AMP OWNER'S MANUAL