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Moscode 402Au Amplifier Review

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An ESL speaker can be notoriously difficult to make relaxedsounding. Most ESL’s I have heard, regardless of size, and even ones with dynamic bass drivers, have sounded intense. The hyper-detailed upper end and speedy transients in the bass cause many of them to make me intense, sitting upright, focused on the minutia in the music. In such cases I tend to become analytical, assessing the sounds in the musicrather than the sound of the music. So, if the speaker has the capability to reveal detail to an extreme degree, there is a good chance that I will find it hard to leave the “critical” mode, to simply relax and engage the music in Toto. It is also one of the reasons I often read while listening when not engaged in reviewing work; call it appreciation by distraction.

For that reason the Moscode 402Au is a Heaven-sent amp for ESL owners. The Cascode (cascade of triodes) George has developed smoothes the intensity of the ESL so that I can relax while listening. As previously alluded, these amps carry a weight and solidity in the bottom-end that is enviable. Even though the Azur and the 402Au spec out close in Bi-Amp mode (The Azur is 200 wpc at 8 Ohms, 350 wpc at 4 Ohms), the sense of import in the sound of a tympani or acoustic bass, not to mention electric or synthesized bass, is greater with the Moscode. From the bottom on up through the mid-bass there are extremely pleasing harmonic overtones with the Moscode. As a result I could relax emotionally more easily as the music flowed a bit more smoothly.

While this may seem a trivial detail, it becomes of paramount importance with a full-range planar speaker like the King, since every bit of bottom-end frequency which can be extracted is precious. Even a perceptually 2-3 additional Hertz is a nice move lower when the speaker is rated at 32 Hz +\-3.

Musically, a good example of this is Steve Oliver’s Radiant, and its third selection “Good to Go”. The electric bass as heard through the Moscode carries a lovely weight, being plump without blurring the notes. The 402Au’s fatigue-free top-end on the King speakers contributed to their exuding efficiency but also effortlessness, a comfortable feel. Similarly, considering vocals, Steve Oliver’s baritone carries strength but also a vocal pliability as he philosophizes in “Bend or Break”,

“Sometimes light as paper or heavy as a stone, we still bend or break.

Yes we all are fragile, just running through our lives, we still bend or break.

The storm is hitting harder as we flutter in the wind, we still bend or break…”

That seems an apt description of the attributes so many are seeking to balance in an amp, strength like a rock but the lightness of paper. We want all the impact and force but also want lightness and quickness as well. After all, have you ever heard anyone boast that their amp is a lightweight or sluggish sounding? The 402Au conducts a fine tight rope act between extreme demands.

Indeed, in a sense the Cascode design does walk a tightrope between the transparency of the OTL and the impact of solid-state. As a tightrope bends and sways just a bit to either side of the person walking it, so also as I sat balanced in the listener’s chair, the amp would stay centered but dance ever so slightly with different artists between tube amp bloom and solid-state clarity. Balance is the key word; the amp never offended the ear. In fact, I think it would be difficult task to match the 402Au in a system and obtain a harsh result. If it can make a pair of hyper-detailed ESLs sound smooth, then it’s not going to drag gravel across your satin-like soundstage.

Rear view of Moscode 402Au Amplifier

VAC Renaissance Sig. and Moscode 402au

There was a preamp/amp combination which won my heart over. Even though in the majority of cases sending the signal direct from the Ayon CD-2 to amp was preferable, the venerable Valve Amplification Company (VAC) Renaissance Signature Preamplifier MkII, when paired with the Moscode 402Au, was unassailable. Here were two top notch products, both with highly refined designs and which mated exceptionally well. In fact, if I had the means, I likely might pursue them as a reference pre/amp combo.

The Renaissance preamplifier is superb at expanding the reach of the acoustic envelope of each instrument, and doing so with startling purity. Mate it with the robust power of the Moscode 402Au and the result is nothing short of spectacular. The joy of it was that the King speakers were up to the quality level of the combo. Indeed, at the time I am writing this, I have already determined to make the King speakers my reference planars, easily so.

I get my taste of orchestrated sound often through rock anthems, a fine, funky example of which is (What else would you expect?), Anthem, by the Taliesin Orchestra. Imagine the oddity of hearing massed strings playing Mike and the Mechanic’s “The Living Years”, or an orchestral version of Eric Clapton’s “Layla”! Let’s just say it’s different; however, the scale of the production is what I’m after. The combination of the VAC pre, Moscode amps and King Speaker is way up therein terms of reproducing the feel of a live concert.Just as fifty years ago OTLs and Quads were the rage, I can perfectly understand itnow that I’m hearing this particular rig! Power, clarity, and that heavenly ESL full throttle, wide open sound is awfully close to “as good as it gets” for the serious audiophile.

402Au with Legacy Focus HD speakers

Lest you think the 402Au is a one-trick pony, only suitable with ESLs, allow me to share the experience of using them with the Legacy Audio Focus HD full-range dynamic speakers. These have a frequency response range of 16Hz – 25 kHz +/-3 dB, yet have a sensitivity of 96 dB! In other words, they are pushing toward the polar opposite of the speaker spectrum from the King. However, the 402Au handled them every bit as adroitly.

The 402Au sounds lush with the Focus SE. I have had some amps which have not been svelte with the planar mid and neo-ribbon tweeter of this speaker. However, the Moscode is right at home with such high intensity drivers, and never made them tinny or piercing. Playing music at elevated levels was a pleasure that few amps I have used can do with ease and elegance, but the 402Au is cut from a very fine sonic cloth.

After the intensive sessions with the King, when it was time to switch to the Focus SE speakers, I dreaded the change, as I thought it might be a huge let down. It was not the case at all in use with the Moscodes. I listened to a fair bit of female vocals as I prepared for the Rocky Mountain Audio Fest 2009. Certain pieces I find gripping, as well as very telling of a system’s capabilities. Two which tell me a great deal are Christina Aguilera’s “A Song for You” and Joan Baez’s “Diamonds and Rust”. The voices of these women take over the room, but not all amps make them sound powerful. With its seemingly limitless reserves and full bodied bass, the amps drew me in such that I was not analyzing but experiencing their voices. That is a big accomplishment, since I am unceasingly analyzing the character of sound no matter the system. When I can be distracted by the sheer beauty of the moment, the components are exceptional.

Tube Rolling


Not only does George endorse tube rolling, his amps are virtual compendiums of rolling options. Printed right on the chassis behind the trap door façade are directions for which tubes are to be placed where, including warnings regarding improper placement. This is one of the most user-friendly features I recall in recent memory, and it treats the audiophile with respect. Many audiophiles have knowledge of tube swapping, but not many are intimately familiar with the myriad of options available. Having concise directions immediately available honors the audiophile instead of intimidating him or her.

George welcomed my request for tubes and sent along two extra sets. Faithfully referring to the manual for placement of the additional valves, I rotated them to see the effect. I was concentrating on replacing the outside pair as the manual indicated that they would have the greatest impact on the performance. My first move, to the RCA 6GU7 in the outside position, resulted in Spyro Gyra’s debut album Moring Dance sounding “antiqued”, with an older air, a stillness and thinness of the air akin to walking into a large auditorium or cathedral which has sat unused for some time. However, when the level was raised the bass began to fall apart – harshness entered and the bottom-end sounded strong, but not terribly full. Seal’s Soul carried a noticeable increase in treble with more sibilance in his voice. He sounded less relaxed, more strained on high notes.

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