World Premiere!
The New Moscode 402 Au Amplifier
This is what I love about tubed components.
Review By Ron Nagle
Click here to e-mail reviewer.

 This 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.

Build Details
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 down 

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”.

Tube Rollers Guide
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.

Ancillary Effects
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 direction.

Aural Aspects
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 else.

Bottom Line, Verity
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 winters night.

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 thing”.

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.

Semper Hi-Fi

Reference System
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 unbalanced digital

Richard 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.

Specifications
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.
Price: $6,495

Company Information
Moscode Inc.
74 Cotton Mill Hill A124
Brattleboro, VT 05301

Voice: (877) 797-8823
E-mail: info@moscode.com 
Website: www.moscode.com