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Basics: Reader Rob Hubertse aka dhtrob - "...upon reading your intro about this VT52 amplifier, I feel the need to share something. Finally we seem to have a commercial product here that applies a non-commercial approach. As a DIYer I have long recognized the need for separate driver and power tube supplies in the same circuit. This is important. Power supplies do have a profound effect on the sound. If the driver tube is fed through a tube rectifier but the power tube through a silicon diode instead the sound is mismatched. Based on your description, this would also appear to be a real power amplifier with appropriate sensitivity. You will need the mentioned 5.5Vrms input (about 3Vrms minimum) to get the full 3-watt output. Yamamoto applies this approach to almost all their models which is good. Most so-called power amplifiers today only need half or less of source output to make full power. Most preamplifiers with gain—be it 10dB or 20dB—become nothing but active attenuators. This you mentioned before but I have never read about a bad S/R ratio when the open gain of the preamplifier—actually the power supply—continuously feeds into too sensitive a power amp.

"And what about microphonics? Using older triodes often results in a gain stage prone to sound pick up, be it by tapping the amplifier (or coming through the floor) or getting triggered by the speakers at high levels. Hitting the pause button on the remote can often result in not immediate silence but sounds starving away. Playing a CD with flute or piano at higher levels immediately reveals whether an amp is microphonic. If so it will have a spacious character. All those little echoes our ears define as extra space.


"The dampening and modifying of capacitors is worthwhile but only if the vibrations come from the same chassis. Remove the power supply from the voltage amplifier by adopting a two-chassis approach and this capacitor mod benefit will be far less. I took apart BlackGate WKZ capacitors to see what's inside. The only difference with other brands was some bitumen damping between can and capacitor. Remove the plastic shrink from application-critical capacitors like coupling or cathode decoupling caps and you will hear a much bigger improvement. Old school sound as you defined it in your A/B comparisons of 300Bs and 45s... now here I think this amplifier will probably fall between the modern EML/KR/EAT and WE/FM/Shuguang schools of sound due to its separate power supplies. Does it make you wonder how good it could be if only there was a modern VT52 equivalent or replacement?"

I'm uncertain which spec Rob referenced to come to his conclusion of a real power amplifier with appropriate sensitivity (he later explained he'd assumed triode rather than pentode-connected C3m drivers). At 0.4V, any wimpy iPod will drive the A-010 to full output. That really makes the Japanese more of an integrated without volume control unlike for example my Trafomatic Audio Kaivalya monos. Their deliberately low 3V input sensitivity places them below the industry-standard 2V for digital sources to benefit from active preamp gain.


Relative to gross microphonics I too had to 'disappoint' Rob. Foot steps or other mechanical shenanigans produced no audible ringing and minimalist fare à la Anja Lechner/Vassili Tsabropolous on ECM betrayed no ghosting. With the ear right up to the midrange driver of my 91dB-specified ASI Tango R speakers there was very mild steady-state surf but no more than with most high-quality valve amps and utterly inaudible from one meter away. Where the quadruple rectifier tubes were concerned, other DIYers active on the forums opined that they were mostly just for show but that only a full schematic could conclusively determine this matter. Indeed. And no manufacturer is obliged to produce such a schematic unless perhaps a customer's foreign service department requires it to facilitate a non-obvious repair. I'm personally inclined to credit Shigeki with far more intelligence than pulling any silly misdirection on rectifiers. My A-09S top-line amp only runs one 5U4G after all. So did my A-08S 45 SET—a single 80 recto—which I later bequeathed to Frederic on staff to have a reference micro-power triode amp on hand. The quad array for the A-010 to me looks simply like a scenario that befitted this specific occasion best.
   
Active or passive? Sometimes banal pop wisdom actually gets it right. The 5AR4-rectified 6SN7s in my ModWright LS100 preamp into the Yammy proved how on occasion too much glass can sound glassy. Literally. Having just the previous night entered far-out inner space over the Burson HA160D/Audez'e LCD-2 headphone combo by marveling over a new conservatory-trained clarinetist's album discovered over the New Year in Instanbul's Tünel district [Göksun Çavdar playing Zülfü Livaneli songs called Şarkilari - Ateş Müzik], I was quite put off by how much thinner, reedier, watery and glassy his Grenadille wood sounded over my main speakers now. It was the proverbial morning-after letdown.


Having used our Istanbul vacation also to shop for a personal G clarinet—actually after play-testing ten different instruments I'd identified Hammerschmidt as the best maker, then decided against being flogged by tourist pricing to instead purchase directly from the Austrian instrument maker which would also reveal more about the operation and allow comparison of various specimens of the same model—I knew very well how it sounds and feels to play this instrument again. The ModWright/Yamamoto team just wasn't it. While I could have drafted Shigeki's own passive preamp into duty, I can't live without remote control. Enter my AVC-based Bent Audio Tap X. This transformation was instant and far-reaching. Now I was in proper Tone Central. Bass too had been too bloomy and big with the active valve preamp. Now I had far superior contour/control and proper amplitude. Subliminal noise levels improved as well. Passive it thus was for the duration of this assignment.




Because of John Chapman's brilliant 1dB-stepped numerical display, let's talk levels. 54 on the Tap X equates to unity gain. At that setting, just two clicks up from mute on the Burson DAC's precision resistor pot netted desired levels from the puny 3-watter (which to be realistic could be driven to distortion slightly above them). In reverse the Burson's pot fully open is supposed to generate approximately 10 volts out. This had the Tap at 10 up from mute, i.e. 44dB below unity gain. With the Burson at approximately 2 volts out (5 clicks up on the stepped attenuator) the Tap-X sat at ±40 to be around 15dB below source output. As you can see, my present listening room is decently spacious, the listening seat nicely distanced from the speakers. There's nearly the same amount of air volume behind the seat. This should give you a useful reference on the A-010's gain/power structure and what it's realistically good for.
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