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Moscode 402Au Amplifier Review

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I repented and replaced the RCA’s with ECC88/6DJ8 in the outside pair. It took only two seconds to comprehend the Russian tubes as vastly richer, sweeter and heavier. An envelope of energy around instruments returned and instead of an antiqued feel, the experience was of a full, glamorous finish. Gone was the Pixie Stix (a child’s confection, a tube filled with sugar), and in its place a mature Crepe Suzette sweetness had appeared. This was a musician’s type of tube, I thought. George had snatched up these Russian tubes which were originally touted as “Virgin Commies” by none other than Gizmo! George says, “He would just make stuff up…” Thankfully, the sound of the Russian tubes wasn’t contrived.

Once I received answers to a few questions I emailed him, George explained that one of the design changes to the 402Au versus the 401HR was the reversal of the tube positions in order to improve noise rejection! All the time I thought I was rolling the critical tubes, I was actually rolling the “wrong” ones. Not that what I did was literally wrong, or that it had nil effect. It simply did not have the most dramatic effect. I would have to return to the rolling to now try the inside pair to get the scoop on the highest benefits of tube rolling in the 402Au.

There could be dangers created by such a misunderstanding between the Manual and the unit. The Manual clearly cautions, “Do not use 6H30Pi tubes in… the inside pair. This is a follower circuit and the 6H30Pi tends to oscillate when used this way.” I might have done that very thing had I not spoken with George. It wouldn’t be fun to cause issues with the amp due to a tardy update on the Manual. If a new manual is not immanent, a letter accompanying the manual showing editorial changes should be issued with the amp. Not all owners are going to research and discuss their actions as much as me, and some might miss performance improvements, being unaware of such changes.

Rolling Along…

Revisiting the tube rolling I was rewarded with precisely the experience George indicated, a far greater impact from tube transitions. Keeping the same sequence of tube changes, this time I swapped the inside pairs. Distinctions between sets of tubes were far easier to recognize, in fact they were holistic in nature. This time, with the Electro Harmonix 6GU7’s glued to their outside position for several rotations, the swapped RCA 6GU7’s inside brought a more powerful, potent, clear Sypro Gyra, as though I had moved closer to the group by 20 rows. A bit of the tonal golden glow was exchanged for this impact. Seal’s voice had more bite and was earnest sounding again. The bass beat greatly tightened up. All in all the character of the sound became more involving.

The best was yet to come, however, when I put the “Virgin Commies” to work (that sounds really evil, but is entirely innocent!). Now I was sitting with the band members of Spyro Gyra, a complete immersion into the group. I could feel the context and involvement of each band member intimately. The soundstage was huge, but the focus had shifted from a smaller, more distant set of instruments with extended ambience to an immediate focus on explosiveness of each note and fullness of the instrument, including each note’s decay. I thrilled to the Xylophone’s wooden notes, as stilted as they are because the bars struck are wood, even having their own musical decay. Seal’s voice was sonorous, sensual, relaxed with no harshness at all. These tubes awakened a marvelous dynamic feel in the King speakers. Even use of four of the Virgin Commies did not top this combo.

Smooth, Like Butta

Each amp has its own native sound, its “voice” if you will. In the case of the 402Au the phrase, “smooth, like butta” is appropriate. I found it difficult to detect rough edges in the Moscode’s characteristic sound. With some amps I have had to work overtime matching equipment, testing cables, rearranging the rig to escape an edginess, a flinty nature to its strength. Even the much esteemed Pathos Classic One MkIII hybrids I so enjoy have fallen prey to this rarely. However, the Moscode was far easier to work with in terms of its ease of presentation.

The 402Au is a tube roller’s dream, and a powerful ally in system matching. With a sea change of sound available to the owner, if something does not seem “right”, send out for tubes, not a new component. You’ll hear vast distinction in presentation from a three-minute tube-ectomy; it doesn’t get easier than with the Moscode. In fact, you’ll end up harboring several sets of tubes because you know the amp can deliver whatever mood of power you’re into lately – antiqued, intimate or nailed-to-the-wall!

This is a classic “music lover’s amp” as opposed to a music analyst’s amp. If you are the analytical type, who wants detail galore, and you do not as much care if there is a tonally tighter, thinner or less plump nature to the sound, then you might not find the 402Au to be precise enough for you. Conversely, if you are moved by the fluidity, the fullness of the notes, the intertwining of the instruments over a parsed separation of the instruments, then you will be enthralled at how placidly the Moscode lays out the music. In other words, the 402Au is like that friendly individual who often seems to be in a good mood, who smiles easily and makes you feel welcome. Sort of like George Kaye.

Manufacturer’s Comment:

First, please accept our gratitude to DAGOGO and Doug Schroeder for such a wonderfully positive review of the Moscode 402Au power amplifier. We are very pleased that Doug heard exactly what we were aiming for.

Doug’s review is very extensive, pairing the 402Au with different speakers and front end components over a period of 6 months or more. Fortunately he makes the point that the amplifier is comfortable with loads under 4 ohms as found in electrostatic speakers. And thank you for the kind words about our service and attention to detail, Doug.

Doug’s comparison with the Futterman OTL amps and Quads is very flattering but not unexpected. Since I was chief engineer at NY Audio Labs back in the day of the OTL, I was exposed to this exact setup and it remains my reference for voicing the amplifier to this day. I have, in the intervening years, brought the Futterman OTL’s performance up to modern standards with regard to power, clarity, bass response and reliability. We currently have a pair of highly modified 200 WPC 10-tube triode OTL’s as our reference. And we also use a pair of modified Quad ESL 63’s that we did some extensive work on to eliminate some of the fundamental flaws of the design. The point is we have a reference system that is unparalleled in transparency.

The big advantage here is that we are not designing to hit a moving target. The mods to the reference gear only served to remove veiling and grunge letting the true character of the gear come out. Sort of like chipping away all the marble that isn’t the statue. But once cleaned up the reference setup never ceases to amaze us at its transparency and effortlessness at rendering detail, no matter how minute. So that has always been the target sound for the Moscode amplifiers since the start.

Lest you think the Moscode is a Futterman circuit with some mods to graft in the MOSFETs, the OTL’s and Moscodes achieve their similar sonic signature in very different ways. The OTL’s are a very high negative feedback design (very much out of fashion today) utilizing about 60dB of NFB, while the Moscode utilizes only about 10 dB of negative feedback to attain its performance. The topology could not be more different. They are different animals, indeed, but give a very similar performance.

Doug talks about detailed analytical sound as a signature of solid state amps and electrostatic speakers. I think what he may be hearing are very transparent speakers that reveal that which comes before it. If the electronics are edgy you will hear edgy. The Moscode was designed using the Quad ESL 63’s because they are so transparent. I can hear subtle circuit changes very clearly. In that sense ESL’s are analytical, but that benefits the product by allowing me to get the grunge out of the way. So when played on cone speakers or ESL’s the amplifier delivers consistent performance.

As a side note, I think our whole industry’s sensibilities have been centered around dealing with a horribly flawed delivery system of music – Red Book CD’s. So much money has been spent and invested in fixing the “perfect” medium. It forces the industry to have to voice our equipment to sound good with inferior source material. Moscode’s design philosophy has always been to go for transparency. So the amp may reveal faults in an inferior front end. Hopefully the 96/24 downloads and advances in digital electronics that are elevating the standards will help get around that issue.

I think hybrid amplifiers such as the Moscode are a class unto their own because they have the potential to do things neither all tube or all solid stated designs are capable of. The only thing I may take issue with is Doug’s comparison with solid state amplifiers in general: “This is a classic “music lover’s amp” as opposed to a music analyst’s amp.” We do take that as a compliment, thank you very much. However, I don’t want people to think that this is a tube-y sound, as in a caramel covered presentation sacrificing detail for smoothness typical of transformer coupled amps. We don’t think there is any sacrifice in detail whatsoever. Quite the contrary. The detail is all there, it just doesn’t burn your ears off with unnatural artifacts that seem to plague many solid state designs. We think it is there just as it should be – as close to live music as we can make it.

George Kaye
President
Moscode, Inc.

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