The New Moscode 402 Au Amplifier
This is what I love about tubed components.
Review By Ron Nagle
Click here to e-mail reviewer.
story begins as I was cruising the halls of the 2008 Rocky Mountain Audio
Fest. I pulled up short outside of room 402Au hoping to find out what
George Kaye was working on. Now George is one of us, you know the type; he
is the kid in the garage burning his fingers learning how to solder. He is
one of those audiophiles who started out with a love of music, boundless
curiosity and ultimately he reached out to share with us.
Flash Back to 1980
Only indirectly through the audiophile underground
did I hear that Harvey Rosenberg, aka: Doctor Gizmo, bought the rights to
the Julius Futterman Output Transformer
Less amplifier from Mr.
Futtermans widow. And following that in early 1981 Harvey Rosenberg set up
the New York
Audio Laboratory to manufacture these innovative amplifiers. The very
first product from Harvey’s company was a (slightly) improved version of
the Julius Futterman OTL amplifier.
Back in June 1983 George Kaye became Chief Engineer of
the N.Y.A.L. Company. Then in 1984 Mr. Kaye developed and introduced the
first true hybrid Tube/Mosfet power amplifiers on the market, they were
the Moscode 300 and 600. After Harvey Rosenberg’s company went out of
business there was a period of years that George Kaye was churning out
aftermarket modifications and upgrades. During this time period he
designed and built Chesky Records recording studio equipment.
He stepped back into the spotlight once more at a 2005
show. There he introduced the model 401HR a hybrid amplifier from the
Moscode Corporation he founded in 2004. So now we move to the present and
bare witness to the premier of his latest evolutionary design. It is the
200 watts per channel Moscode 402Au. This is a Hybrid Dual Mono Stereo
Amplifier with a Class-A tube driver stage upfront and solid state
Mosfet’s driving the speakers. The last two letters of the model
designation are the symbols on the periodic table for gold. The circuit
layout has been redesigned, the components used have been upgraded and the
heavy copper circuit traces are now gold plated. All of these and many
other advancements promise to lower the noise floor and refine the sound
beyond what was possible before.
The overall build quality is
absolutely first rate with 14 gauge steel used for the chassis. It uses a
dual mono power supply rated at 200 wpc at 8 Ohms and there is 88,000 mF
of storage capacitance for each channel. The circuit parameters are many
so I will include a list at the end of this evaluation.
The amplifiers power switch is a push button located in
the center of the front panel. There is a
rectangular opening in this half-inch thick aluminum panel holding a glass
plate engraved with the company logo. The glass plate is illuminated at
the edges by a blue light and serves as an operational status indication.
When the amplifier is first turned on the glass illumination alternates
between two levels. After a 45 second delay the power muting relay closes
and the display remains brightly lit. In the event of an amplifier
overheat condition the glass logo will turn red until the amplifier cools
The most striking and for me intriguing aspect of the
new 402Au is the prospect of an all out tube rolling orgy. Let me explain,
I am basically but not solely an audiophile afflicted with Audiofilas
Tubularis that is a person who likes to experiment with tubes.
The Moscode amplifier has a power interlocked trap door style faceplate
and when opened you have access to the four tubes that comprise the Class
A input circuit. This circuit is a simple 2-stage class-A triode
driver stage. If you are like me and you have drawers full of New and Old
Stock vacuum tubes the possibilities are simply erectile. Seriously, the
ability to adjust the power amplifier and tailor your system sound to
match your listening environment and musical interests is no small thing;
as a matter of fact the Moscode Company encourages it. When you open the
front panel there is a tube guide printed just below each tube position
showing compatible tube types. Remarkably the 402Au has an Auto
Filament Switcher circuit that is unique among tube-powered
amplifiers. It will sense and instantly switch to accommodate either 6 or
12-volt center tapped heater filaments. Ultimately you understand that
this allows for so very many dual triode combinations that you should
never run out of great sounding tubes. The 402Au comes supplied with a
pair of EH 6CG7 and a pair of Sovtek 6H30PI tubes. The 6CG7 is listed as a
medium Mu (gain) twin triode and the 6H30PI is a low Mu (gain) double
triode. Looking at the rear of the amplifier there is an IEC line cord
socket a 10-ampere fuse and a pair of gold plated Cardas RCA sockets. Most
notably there is an input Stereo/Bi-Amp toggle switch that configures the
amplifier to mono and allows two amplifiers to drive speakers with two
separate inputs and crossovers. At the center is a front panel light
dimmer control and notably a pair of oxygen free solid cooper Edison Price
speaker cable binding posts. Internal wiring is kept to a bare minimum and
is by Cardas. The Owners Guide recommends approximately “25 hours to
open up and a good 100 hours before performing its best”.
What follows is excerpted and condensed advice lifted
from the very informative owner’s manual.
The first stage of
tube amplification does not use negative feedback around the circuit so
the gain of the tubes used determines the overall gain of the amplifier.
For those who want
to fine tune your systems sound start with the two outer tubes in
positions V101 and V201. These tubes provide voltage gain and they will
make the most sonic difference. Do not use the Russian 6H30PI in these
positions. The two other inside positions, V102 and V202 have much less
effect on sound.
In general when
using, low Mu (gain) tubes like, 6FQ7, 12AU7 and the 6H30PI the sound will
be smoother and less aggressive with more forward imaging.
Medium Mu tubes like
the 6DJ8/6922 can extend the high frequency response and tighten the bass
most likely the sound stage will appear to be deeper.
Before I try to describe very specific tonal
characteristics of this amplifier let me talk about my little experiments.
The designer George Kaye told me he likes Cardas Golden Cross cables but
he encouraged me to experiment by swapping interconnects and speaker
cables. He was right, I started with Kimber 8TC cables to my four way
Strata Mini speakers then exchanged them for the newest Kimber 12TC. Next
I Bi-Wired, using two pairs of Kimber Kable’s. The 12TC went to the mid
and tweeter drivers and the 8TC was connected to the bass. I gained a bit
more extension at the bass and treble frequencies. Next I swapped
interconnects. I installed 3 meters of Kimber Silver Streak between my
Audio Research SP9 Mark 3 and the Moscode 402Au amplifier. Each
substitution that I made yielded more extension and opened up the sound
stage a bit more. Bottom line, try a little system fine-tuning the
amplifier will respond and tell you if you’re going in the right
Understand that my evaluation and any final comments
that I make has to be based on the tubes that were supplied with this new
amplifier, however I just might do a little tube rolling later on. The very first in your face characteristic that I heard
was more gain; I had to trim down volume to keep the neighbors from
squawking. As a reminder you do have the option of using lower Mu tubes to
customize your system gain.
We all know your not supposed to listen critically until
you put a couple of hours on anything new. But in passing I did notice a
softly rounded bass in those first few hours. The bass slowly improved as
the 402Au burned in. Farther along at about 25 hours I did tune in and
noticed something I value very much. What might that be you ask? Well
bunky it’s the expanded space around individual elements of the
recording. It may be subtle but its there. This is an effect not only of
placement but the inclusion of harmonic information that lets you hear for
example the resonant wooden body of a piano or cello. It is most revealing
in the upper mid range and when listening to vocals. What you get is an
envelope of information that further defines what you’re listening to.
This is exactly what digital class D and even some transistor amplifiers
get wrong. They do get the initial attack (jump factor) but do not resolve
the natural decay of the instruments. With digital amplifiers it seems
that once the source volume drops below a certain numerical value it
becomes an insignificant bit. Contrastingly I recently purchased a very
neutral sounding four thousand dollar Bi-Polar powerhouse (1.Kw/2 ohms)
solid-state amplifier. It was exactly what I needed, no matter what type
of speakers I might have to review. It will drive anything out there
without imposing itself on the performance. But now a stereotypical
audiophile conundrum confronts me. I don’t need but I want the $6,495
Moscode 402Au it has a melodic voice that speaks to me. Understand it is
not too Single Ended amplifier dark and not too Class-D amplifier bright,
it’s just about right. It does great things to a sound stage it is wide
and it is especially deep casting a wonderful harmonic surround around
every thing in the musical mix.
Let me get very specific, when I listened to Frank
Sinatra singing, “What’s New” from the album Only
the Lonely [Capital 48471]. The vocal inflections the breath
sounds describe an organic quality that places him in the room directly in
front of me. The sound of the bass line was deep and slightly warm but you
could better hear small inflections like the husky reed overtones of a
Baritone Saxophone. Admittedly you can get tighter bass control with a
bi-polar amplifier but than you would have to further sanitize everything
In a world of tradeoffs I would rather see and hear into
a deep and wide soundstage that liberates me from my small room. That is
something that I value very much, transport me believing into the
performance and then count me content. Surely this is a right brain left-brain problem for me
and in this case both sides are correct but for different reasons. I believe that the inclusion of tubes operating in
Class-A lends an expansive and lifelike quality that I want. The Moscode
402Au is the amplifier I would chose to sit and listen to on a cold
Oh what to do, maybe I can hide it from my wife? Or
I’ll tell her its on loan. Nah! That won’t work, eventually she will
find out and I know exactly what she will say.
“But didn’t you just buy that other amplifier
George this is all your fault I didn’t see this
coming. This is what I love about tubed components the options the
possibilities last long after the wedding night and even after you carry
it across the threshold. You have 33.3 day’s to listen to this amplifier
in the comfort of your own home, I think you will like what you hear.
I feel sorry for the solid-state guy, as they are most
certainly solidly stuck in that state. If you want an amplifier with
power, finesse and adaptability than this is as close as you will ever get
to having your cake and eating it too.
Marantz DV 8400
Universal CD player, Cambridge Audio Discmagic-1 CD transport, Cambridge
S-700 Isomagic HDCD D/A Converter, ART DI/O Up sampling D/A and A/D
processor, Magnum Dynalab FT 101a tuner and Dynalab Signal Sleuth.
Roger Sanders ESL Power Amplifier, Onix Rocket Strata
Mini 4 way speakers by AV 123, Aurum Cantus Leisure 2 SE two-way monitors
on 24-inch stands.
Three-meter, Synergistic Research Alpha Quad X Series
speaker cables with active shielding.
Three meter Kimber Cable 12TC, 3 meter Kimber Silver Streak
RCA, 3 meter, Wire World Eclipse-2, RCA, 1 meter Chord Silver Siren, 1
meter and Wire World 10 gauge IEC power cord, Audiobhan 0.5 meter
Gray 20 Ampere Substation, Islatrol Industrial 20 Ampere ac line
conditioner, Alpha Core Balanced Transformer Power Supply, Audio Power
PE-1 power enhancer, Triad 2-Ampere isolation transformer
VPI Magic bricks, Argent Room Lens system, Room Tunes
Panels, a comfortable chair.
Type: Tube amplifier
Serial Number: M 402B 08 0051
Direct Coupled Output Transformer less Amplifier.
Power: 200 Watts RMS @ 8 Ohms: 300+ Watts @ 4 Ohms
THD @ full power: (tube dependent) with 6H30Pi, 0.15% at full power.
Noise: Inputs shorted <1.mv. Voltage Gain: (tube dependent) 30 to 33 db.
Tube Complement: 2x 6H30Pi and 2x 6GU7 supplied
Substitutions: 6DJ8, 6922, 6FQ7, 5814, 7730, 12AU7 should be used in pairs
Connections: Input, Cardas Gold RCA, unbalanced, 100K input impedance
Output: Edison Price Music Posts.
Rear Panel Toggle Switch: Configures amplifier for Stereo or bi-amplification in Mono.
Dimensions: Faceplate 19 inches wide
Chassis 17.5 x 14.5 x 6.25 (WxDxH in inches)
Shipping Weight: 52 lbs.
74 Cotton Mill Hill A124
Brattleboro, VT 05301
Voice: (877) 797-8823