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Reviewer: Srajan Ebaen
Financial Interests: click here
Source: Ancient Audio Lektor Prime, 1TB iMac with AIFF files via FireWire 800 into Weiss DAC2, via Entreq USB into Wyred4Sound DAC2 [on review]
Preamp/Integrated: Esoteric C-03, Burson Audio 160 [on review]
Amplifier: FirstWatt J2 & F5, Burson Audio 160 [on review], Wyred4Sound ST-500 [on review], ModWright KWA-100 [on review], Trafomatic Audio Kaivalya
Speakers: ASI Tango R, Zu Essence
Cables: Complete loom of ASI Liveline
Stands: ASI HeartSong - 2 x 3-tier stands, 2 x amp stands
Powerline conditioning: 1 x Walker Audio Velocitor S, 1 x Furutech RTP-6
Sundry accessories: Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; extensive use of Acoustic System Resonators, noise filters and phase inverters, Advanced Acoustics Orbis Wall & Corner units
Room size: The sound platform is 3 x 4.5m with a 2-story slanted ceiling above; four steps below continue into an 8m long combined open kitchen, dining room and office, an area which widens to 5.2m with a 2.8m ceiling; the sound platform space is open to a 2nd story landing and, via spiral stair case, to a 3rd-floor studio; concrete floor, concrete and brick walls from a converted barn with no parallel walls nor perfect right angles; short-wall setup with speaker backs facing the 8-meter expanse and 2nd-story landing.
Review Component Retail: $3.600

Nelson Pass on the M2
: "I created an amplifier using a transformer for voltage gain. Despite its mediocre measured performance, I thought it sounded quite good. I still had some misgivings about taking it to market particularly at the same time as the J2. But then my Japanese distributor asked to hear it so I sent them a prototype. Next I received photos from the Japanese show. Then a prominent reviewer committed to a review. Suddenly I had a lot of interest from all over Asia."

In the FirstWatt catalogue, the M2 follows the J2, with M for Mosfet, J for JFet. It's the only second amplifier in the range to sell through dealers and distributors. The previous six, F1 through F5 plus Aleph J, sold only direct. They also were limited editions of 100. Like the J2, the M2 will be made in higher volumes. Like the J2, it also does 25 watts into 8 ohms, runs in pure class A and avoids negative feedback. Where it differs is in the voltage gain stage. Here it's passive. An input autoformer replicates what a step-up transformer does for an MC phono stage. It magnetically multiplies the input voltage. Inverted, this also relates to transformer volume controls. TVCs use multiple secondaries on transformers or autoformers to step down the input signal in discrete steps. Some TVCs even offer up to 6dB of gain. They will also step up the input voltage by a small amount instead of just working at or below unity gain. And stepping up is exactly what the M2's autoformer does - by a gain factor of five times or 15dB.

Transformers tend to limit bandwidth. It's a contributing factor to the tube sound which sends amplified signal through an impedance-matching output transformer. Hence OTL tube designers abolish output transformers. With FirstWatt, the output devices of choice have always been transistors. Though transistors can couple to speakers through output transformers—McIntosh amplifiers do—the FirstWatt amps haven't. Thus far.

But repetition is the mother of boredom. Nelson Pass seems to hate it like most creative folks. So the M2 does use signal-path iron. It simply puts it at the circuit's beginning, not end. Impedance matching—to the source rather than load—occurs via a complementary JFET pair. It acts as a very low distortion input buffer and sets the input impedance at 100 Kohms rather than the 6K which the autoformer alone would present. This welcomes valve preamps. Of course signal path transformer limits on bandwidth, phase shift and slew rate remain. That's why most transistor amp designer shun them. Why not the M2? Many tube amps measure poorly. Or not as good as most sand amps. Even so—or because, at least in part—they often sound from good to terrific. If valve amps can pull that stunt, why not transistors? It's a question the M2 seems to ask. Put differently, many moons ago Bob Carver met a well-publicized challenge to make a transistor amp sound indistinguishable from a valve amp. His approach involved manipulating the sand amp's transfer function and altering its output impedance. Nelson Pass makes no claims for outright tube sonics.

But, "...the M2 does have some of the qualities SET aficionados look for. The autoformer brings its own signature to the sound, albeit in smaller doses than usual. The midrange has a lush warm character which I associate with tubes and transformers but subtly so. Part of this is due to the limited bandwidth of transformers, part of it is the lack of feedback artifacts. On the other hand, there is considerably less harmonic distortion than with no-feedback SETs. If you really do like that distortion, then the M2 might not be what you want. Also, there is more power than usual and a relatively high damping factor. So in those regards the M2 differs too. The only thing special about the autoformer is that it won the listening tests for reasons unknown. To avoid the inevitable cloning, I am withholding the details of its manufacture. Funny thing about that - I can give enough information about a circuit that real DIYers will be able to more or less duplicate it. But if I don't fill in all the part values, the commercial cloners are discouraged because they can't promote it as authentic."

Nelson's new paper on a Jean Hiraga-based, Jan Didden-inspired Arch Nemesis DIY amp project kicks off with these words: "A poster of Einstein once said, things should be made a simple as possible but no simpler. This can apply to audio amplifiers but if they are evaluated subjectively, the simplicity thing can get a little out of hand. Of itself, minimalism exerts a strong aesthetic attraction and there is a reasonable belief that fewer components in the signal path allow more information to get through with less coloration. If like me you are interested in understanding how we hear distortions with our brains—instead of our meters—you might appreciate that simple circuits help isolate these phenomena. I listen to all sorts of flawed circuits because I enjoy hearing the differences and it helps to train my ears. In this regard, reducing the number and types of flaws makes it easier to tweak a single parameter and hear the difference. I think it's also true that simple distortions are often more forgivable in a listening situation and create less fatigue."

Jan Didden will publish this very interesting paper in the first issue of his new Linear Audio printed bookzine, to hit the streets September 1, 2010 with 100+ pages of tech audio and perception articles. An accompanying website with capsule previews of the print articles and related materials will launch a few weeks prior. Here's a guest editorial Jan wrote for Audio Xpress that's nicely relevant to all critics of other people's works while explaining the allure of DIY.

SET (de)lite without the sins? The M2 was an intriguing proposition that just begged for an investigation. Because all FirstWatt amps share the same chassis to save production costs, their class A power output is necessarily limited by what these enclosures with their fixed heat sinks can dissipate in heat. At 25/40wpc into 8/4Ω, the M2 is no arc welder. Compared to the usual triode amps however, it's rather beefy. And affordable. Its output impedance is obviously much lower than the single-digit figures of no-feedback SETs. This benefits frequency response linearity and control. It also diverges from the recipe of why tube amps sound like they do.

It would thus be very interesting to learn how this and the overall lower distortion might alter the overall sonic gestalt; and how much 'tube flavor' the overlapping aspects of class A operation, simple circuitry and transformer windings in the signal path could generate. Conceptually, I expected a between-both-poles presentation, albeit a tad closer to the valve polarity than dead center.

For comparison, I not only had two classic 300B SETs—the Yamamoto A-09S and Woo Audio Model 5—but also the Burson Audio 160 amp/buffer. The latter is a 95/180wpc into 8/4-ohm class A/B transistor amp. Unusual about it are high-level inputs to boost the drive power of 5-25wpc SETs. Then it acts as pure current buffer like Nelson's own F4. This option—SET + transistor buffer—would give me another variation on the general theme of coaxing recognizable valve virtues from solid-state without any ambitions of cloning them outright. After all, where would the creative challenge be in just cloning? That's best left to unimaginative copycats.