October 2013


World Premiere!
First Watt / Pass Labs SIT-2 Stereo Amplifier
10 excellent watts!
Review By A. Colin Flood

  On several systems including mine, the SIT-2 did not sound like a tube amplifier. It was better in some respects. Nor did it sound like solid-state either. It was better in many respects there too. The new Static Induction Transistor SIT-2 stereo amplifier from Pass' First Watt company is a plain dark-gray box. Sure, it has signature Pass cooling fins sticking out at an angle like Batman's car, but small, bright blue LED eyes replace the famous big, blue Pass meter. The amplifier doesn't look monstrously powerful. It isn't either. Intended so its first watt is the best, the SIT-2 amplifier is rated at only 10 watts output. Designed to sound like tubes, instead the SIT amplifier does not sound like solid-state.

Of course, a solid-state amplifier that sounds like tubes seems ideal. Especially for my Big Ole Horn loudspeakers (see my Reviewer's Bio). Therefore, I auditioned the SIT-2 gray box with the blue eyes in a variety of systems, not just my horns, but on other systems too.

The new SIT-2 is half the price of the original monoblock amplifiers; it offers two channels for the price of one monoblock. The SIT-1 monoblock offers adjustability of the operating point and is biased by a big chain of power resistors instead of the constant current source used in the SIT-2. In this way, the SIT-1 is totally surrounded by passive components. The cost comes in efficiency — the efficiency of the SIT-2 stereo amplifier is about 12%, while the efficiency of the SIT-1 monoblock is about 6%. While the SIT-2 provides maybe a single watt, at most, to drive horns  to normal 70s sound pressure levels (SPLs), it still draws 200-watts off the wall. Both SIT amplifiers offer the same maximum output of only 10 watts per channel.

The stereo version does not offer a bias meter and adjustment potentiometer. The SIT chip combines a square-law input character with a low impedance output to form the only solid-state gain device, which Pass claims, "behaves like a triode tube." See Nelson Pass talk more about his exciting new designs in SET and SIT Amplifiers article for Enjoy the Music.com. There is no output transformer on the SIT-1 or SIT-2. The point of the SIT is that it behaves like a triode but at lower voltages and higher currents, so it doesn't need a matching transformer to deliver power to 8 Ohms.

Input Impedance
Without the buffer stage, the SIT-1 monoblocks' inherent input impedance is 10 kOhms, which should not be an issue with any line preamp sporting a source impedance under 1 kOhms. But in order to ensure compatibility with any preamp or source component out there, both the SIT-1 and SIT-2 units offer an optional FET buffer that provides a 100 kOhm input impedance option. Input impedance selection (10 or 100 kOhm) on the SIT monoblocks is performed by means of a gold jumper which plugs into an XLR connector near the RCA input jack. Switching the jumper switches the input impedance. Pass says the 10 kOhm setting is of course more purist in nature, as it bypasses the buffer stage. The 100 kOhm input impedance is "for people with passive volume controls," Pass said, "and pitiful preamps that can't drive 10 kOhm. I find that almost no one uses it."

The manual for the SIT-2 amplifier is informative and entertaining. It is on line at www.FirstWatt.com. The manual provides SIT details and distortion curves. The SIT-2 packaging meets my approval: two-three inches of Styrofoam brackets, (necessary for the UPS bounce test), along with a plastic moisture barrier bag. The SIT-2 does not have balanced outputs, which would be nice at this level of refinement. Though not quite as huge and impressive as the thumb-size speaker cable binding posts on the Pass Laboratories Supersymmetry Balanced Single-Ended Class-A X250, which I reviewed, yet the smaller versions are just as easily reached and usable.

In many sonic respects though, the revolutionary SIT-2 design resembles the sonic aspects of mighty Pass amplifiers like the X250. The SIT-2 had no problems with thundering bass notes and never seemed to run out of power on most music at normal listening volumes. On my horns and on a pair of full-range cone loudspeakers, the SIT-2 always seemed much more powerful than mere 10-watts. Like the X250, only on the deepest, most complex crescendos, did I notice that the SIT-2 was not the equal to the far more powerful Pass monster amplifier. This is a remarkable achievement for amplifiers, designers and the industry. It certainly did not sound like a low powered amplifier. The SIT-2 was the best solid-state amplifier I have heard on Big Ole Horn loudspeakers.

In his thorough tour of the interior components of the SIT-1 monoblocks, Dick Oshler said the Pass design is "a sonic home run." He said the SIT sounds "like a superb 300B based SET but with far more transient speed and extension at the frequency extremes. There's plenty of soundstage transparency and dimensionality, as well as superb layering of the depth perspective."

Comparisons
On several systems including mine, the SIT-2 however did not sound like a tube amplifier. Listening in the low 80s sound pressure levels (SPLs) on a slow, C-weighted scale — as measured by an uncorrected Radio Shack analog meter — my pre-amplifier indicated about half-power at noon on the dial. The SIT-2 did not have the sweetness of tubes; it was leaner, not as bloomy bass. More treble friendly. The SIT-2 sounded artifact-free. It had wider separation and improved distinction to the instruments.

Of course, with only 10-watts maximum output, it was easy to dial full power on the dark gray box. Yet, the slide up the SPL scale never sounded harsh. This was something I could not do even with Don Garber's wonderful 1.5-watt Fi amplifier! At full power, SPL was only mid-90s — not the amplifier I need for rock music. While treble instruments stand out from others better, there is no deep feeling to the lowest bass notes. Yet, the SIT-2 never showed any strain or clipping.

Danny Boy
The Bryston is a solid-state stereo power amplifier, rated at 120-watts continuous into 8 Ohms (20.8dBW), and 200-watts per channel continuous into 4 Ohms (20dBW). It retails for $1565. Up against the well-regarded Bryston 3B ST amplifier on custom, 6 Ohm floor standers (ScanSpeak drivers, vented, 2.5-way towers) in a small, cluttered but open room, the SIT-2 did not show many apparent differences at first. Jacintha's has an enticing 20-bit XRCD rendition of the classic Irish folk tune "Danny Boy." On it, the SIT-2 horns were shaper, almost strident, more blat, but less of the smoother blare, which together makes such instruments so beguiling. The SIT-2 had ample mid-bass, but not enough for the lowest notes.

Switching to Igor Kuznetsoff's $325 silver Empowered power cord produced almost as much difference as switching between the two amplifiers. There was more texture and details. But the result was too bright for my liking (review coming). Also up against the SIT-2 on this system and my Big Ole Horn loudspeakers, was the new Glow Audio $1508 integrated amplifier Two (review also coming). This charming, white EL84 tube amplifier is indeed the sweet tube sound... and its weaknesses too. Side-by-side, the SIT-2 is no tube amplifier. It has none of the warm, organically full midrange and soft treble sparkle of even a tiny EL84 tube on Big Ole Horn loudspeakers.

But it also had none of the grating solid-state edginess (odd-order harmonic distortion) that drives tube lovers over a cliff. The chart of its Total Harmonic Distortion is a steady slope, a smooth climb, albeit to low power altitudes. In fact, the SIT-2 sounded much less defective or annoying than any other solid-state amplifier I have auditioned on Big Ole Horn loudspeakers!

On Big Ole Horn loudspeakers, in a big wood room, 15 by 30 feet, half sloped to a two-story 22-foot peak, soundstage with the SIT-2 was vast, separation excellent. First impression was of cleanliness, but not brute power. It was sharper, bright but not sparkling. The treble was accurate, with some clinical dryness, though not hard edge as most solid-state amplifiers. If the price was lower, this would be the solid-state amplifier for many Big Ole Horn lovers.

Solid Choices
A typical audiophile quality cone driver loudspeaker, with a typical 85dB/W/m efficiency, may require less than one watt to reproduce conversational SPLs about 10 feet away. Yet for brief microseconds, musical peaks 30dB higher at full volume, will require as much as a staggering 4,000 peak watts! The answer for solid-state lovers is something like the amazing $195,000 Boulder 3050 amplifier, with 4,000 watts into 2 Ohms! The answer for tube lovers is the soft clipping characteristic of tubes.

Pass accomplishes soft clipping with this new solid-state design. Its low-rated power belies the strength of this design in many Enjoy the Music.com categories. While tweaking audiophiles might want another solid-state amplifier driving their woofers, I would put this amplifier up against any solid-state amplifier of any power rating on above-average efficiency loudspeakers.  Its sonic footprint does sound bigger than its shoes. In this regard, the SIT-2 played most kinds of music with excellent transparency, rhythm and dynamics; always sounding more powerful than rated. The soundstage was impressive. Images are life-sized, without the holographic 3D imaging of a really good tube amplifier. Tonally, the SIT-2 exemplified the well-worn term of neutrality more than any solid-state amplifier I have reviewed yet.

I think the SIT-2 midbass is solid like the similarly-priced Jaton Operetta A2300AX Stereo Power Amplifier. Nelson Pass accomplishes with a 10-watt Static Induction amplifier what Jaton does with 300 Class A watts at 4 Ohms! Two other nice sounding solid-state amplifiers on Big Ole Horn loudspeakers bear mentioning. One is the "The Sexy, More Powerful, Roksan Caspian Integrated Amplifier" I reviewed almost ten years ago. I said "It Sounds As Good As It Looks." The Roksan colored everything in a silver sheen, slathering more soft butter than any Brit would spread on a biscuit. Nonetheless, it was an enjoyable performer for a quarter of the cost of the SIT-2.

The second is the Outlaw receiver that made the company famous. Stereo reviewer John Atkinson personally recommended the famous Outlaw Audio RR2150 stereo receiver to a friend of mine for his Khorns also. The Outlaw receiver opened my mind to the potential of solid-state amplifiers on Big Ole Horns. It too was a very enjoyable solid-state amplifier, for a tenth of the SIT-2 price!

Also in the running is the integrated solid-state Synergy Control amplifier from Audio by Van Alstine (World Premiere review coming). This is a 100-watt per channel amplifier, with 47 kOhm input impedance on all sources, for $1799. It is not lush like the Roksan, powerful like the Jaton or gentle like the Outlaw, yet first impression is of a delightful and capable contender. No amplifier I have ever auditioned on the same system in the same room with the same music for Enjoy the Music.com has ever sounded exactly the same as any other amplifier when playing demanding passages, such as a large rock band or full symphony orchestra, at louder than normal sound pressure levels!

I have auditioned maybe a dozen amplifiers at home and several dozen on other systems.  I have not heard two of the same amplifier models, except for my own Bottlehead Paramour 2A3 monoblocks. These amplifiers are not marked for right or left channel, yet over the years, I have never noticed any difference between the two. I can say, and did publicly, than when my Class A Pioneer M-22 drove my classic Klipsch corner horns, I did not hear enormous differences between it and the amazingly powerful Pass X250, with regular music passages at normal volumes. Therefore, the big audible difference between amplifiers is probably due mostly to at least two major measurable characteristics: impedance control and clipping.

Because of its lack of detracting artifacts, I rank SIT-2 tonality as above-average compared to other amplifiers auditioned. With only 10 watts maximum output and other reasons, the sub-bass of course is a typical tube amp ranking. The SIT-2 may ranks as average, though felt that inner resolution provided the ability to hear into the details of the music was improved. So I awarded it as above-average in this category too. Sound Scape is an especially hard category to review on Big Ole Horn loudspeakers. Because of their size, projection, clarity and enormously wide dispersion, most other systems seem narrow and congested in comparison. Belying its low power, like other Pass amplifiers I have heard, the SIT-2 has the important ability to play a numerous instruments simultaneously side-by-side and with good separation. Apparently giving each one enough energy to sound whole and complete. The First Watt site describes this as "exceptional localization." The First Watt SIT-2 ranks well in the imaging department.

Was able to crank the SIT-2 to full power with no sound of distortion or fatigue either from the amplifier or the mighty Khorns. Although Big Ole Horn loudspeakers are so efficient they tell you everything they hear upstream from them, I ranked the SIT-2 above average in Self Noise because I never heard a whisper of gossip from it, even at full volume. As for my own enjoyment, the bottom line is above-average enjoyment for a low powered, solid-state amplifier on über-efficient horns. Therefore the revolutionary new Nelson Pass Static Induction Transistor stereo design is definitely an above-average value for the money for anybody that can fit 10 excellent solid-state watts into their system.

Specifications
Type: Solid-state stereo amplifier
Frequency Response: 4 Hz to 500 kHz (-3dB) 
Output Power: 10 watts @ 5% THD, 1 kHz
Distortion @ 1 watt: 0.7%
Input Impedance: 10 kOhm / 100 kOhm
Gain: 18 dB
Output Impedance: 4 Ohms
Noise: 150 uV unweighted, 20 Hz to 20 kHz
Power consumption: 200 watts
Fuse: 3AG slow blow type -2.5 Amp for 120VAC, 1.25 Amp for 240 VAC
Weight: 32 lbs.
Dimensions: 17" x 15" x 5" (WxDxH)
Warranty: Parts and labor for 3 years, not covering shipping costs or consequential damages. 
Price: $5000

Company Information
First Watt / Pass Laboratories,
13395 New Airport Rd,
Suite G
Auburn, CA 95602

Voice: (530) 878-5350
Fax: (530) 367-2193
Website: www.FirstWatt.com