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Equipment Review
April 1998

Three Is Enough? Three's a crowd?
Moth Audio Corporation s2A3 Amplifier

by Steven Rochlin

Last month's review (by me) of an awesome, killer, almost $8,000 phono cartridge was fun (Clearaudio Insider Gold Cartridge), yet now it's time to get back to reality, or is it? It's time to bring down the equipment price by quite a bit, yet the product at hand, which is less then half the price of the Clearaudio cartridge, will probably be for an even more obscure audience. Only the truly dedicated experimenter will even consider buying this piece, yet once all is in place, the beauty of music might come and hit ya smack in the nose! After all, when you're tryin' to trip the light fantastic to find that hidden beauty, you gotta kiss a lot of frogs to find your princess. On SoundStage! Talk Online there have been quite a few questions about speakers to use with lower-powered amplifiers. My hopes here are to give some insight to a few matters at hand as we usher in the new Moth Audio Corporation s2A3 unit.

The 300B tube, as many of you are quite familiar with, is usually run single-ended and can achieve an output of about 8Wpc. I know, I know. With only 8 watts, what kinda speakers can you use? Well, the 2A3 tube is also from the same "old school" as the 300B and, like the 300B, it's still being made today. Unlike the 300B, the 2A3 has an output of a huge, monstrous, city-shaking 3 watts or so when run in pure class-A single-ended mode. No! WAIT! Hold on a moment! Please don't hit the back button on your web browser so fast! Please humor me here. Pretty please. OK, where were we? Oh yeah...3 watts output or so. The trick with many low-powered units is to find high-sensitivity, smooth-impedance, great-sounding speakers. Horns are one obvious option. Specialized dynamic cone speakers like those offered by Lowther for many decades are another. Still other options are to just shop around for a speaker that meets the criteria of high sensitivity and smooth impedance and then possibly mate it with a self-powered subwoofer or two for the lowest few octaves (which I do). Why do this? Please read on.

Most speakers are really nothing more than motors with the job of moving air. A motor that needs to move less air (a tweeter, for example) works less and therefore needs less power than a motor that needs to move more air (a subwoofer). Of course, the size and acoustics of your listening room also play a part in the story here. If you have a huge room (or a very acoustically absorptive one), the motors need to move more air to fill the room with sound. This is kinda how we also get sound pressure levels (SPLs). The act of the speakers moving the air "pressurizes" the room per se. The speakers moving air causes pressurization, and thus the more air the speakers move, the higher the pressure levels (volume). By careful planning, crafting, and grouping your system, a harmony may be found. As for me, it was just dumb luck. Go figure. As for the smooth impedance, may I simply say that a majority of tube units use an output transformer to better match the electrical output from the amplifier to the speakers. Seeing as this transformer has been made to accommodate certain impedance(s), for best results we all should find speakers that closely match what the transformer was designed to "see" (said in humor). Now remember kids, there will be a test on all this next week! Enough already with the foreplay! It's time to get down and dirty.

The Moth Audio Corporation s2A3 amplifier is capable of 3Wpc output and uses the 2A3 tube in class-A single-ended mode with no feedback. This unit has a volume control on the front panel that is always in the circuit. This means if you have only one source component there's no need for a preamplifier. Also on the front panel is a new twist you virtually never see with high-end gear, a headphone jack. Now you probably realize that 3 watts should be more than enough for comfortable music enjoyment with headphones, but with speakers? The output transformer is made by the well-respected Electra Print company and can be set to drive 2-, 4-, 8-, or 16-ohm speakers. There are only two triodes per channel directly in the signal's path. One 6SL7 dual triode is wired in parallel to drive the 2A3 output tube per channel. These tubes are direct-coupled by the way -- no capacitors in the signal path. Both tubes are cathode-biased and require no adjustments. The power supply uses a 5AR4/GZ34 rectifier tube (in a RC, LC, LC filter network for those of you with technical fetishes). The power transformer and filter inductors are all low-flux-leakage, torroid designs. This type of design helps to keep the power-noise yukkies from affecting the rest of the electronics. In addition, Moth Audio Corporation uses low-noise regulators for all filament supplies. Input RCA jacks and speaker output binding posts are of very high quality and made by none other than Cardas. The Cardas speaker binding posts are my personal faves, by the way. I wish more manufacturers used them. Why? They can take a lickin' and keep on....

Cosmetically, the Moth s2A3 has a retro tube-unit look. Even the nondetachable power cord has that old-time cloth covering. Actually Moth Audio Corporation's whole line has this retro look, and I find it very appealing. The chassis/unit is so solid that I betcha it could be thrown against a wall, put a hole through the wall, and not damage the unit itself. Then again, when a unit sounds this good, why would you wanna do that? Speaking of sound, it's about time I shudup and get to it already!

Three watts. Gosh, well, um. So watt can they do? Given the right speakers here's watt they can do. With the Moth 2A3, the music can be wonderful, but not in the overly euphoric sense. In fact, with the stock tubes, the music sounded just a smidgen sterile -- just a touch, mind you. Meanwhile the speed of attack, the ability to follow even the smallest timing cues, the very small dynamics within the music, were absolutely amazing. I gotta admit, 3 watts on the various speakers I used did an amazing job. They produced a deep soundstage and very good width, very nice overall. Yet the harmonics sounded a small bit sterile. What got my attention was how very good the bass was. In my room, in the various systems this unit was used in, many folks who came to visit were amazed at the sound this 3-watter was making. In fact, one person couldn't believe the unit was only 3 watts (he has big Krell amps, by the way). Still, it was that touch of sanitary sound that irked me.

So upon popping the hood, I found there was one Chinese 5AR4/GZ34 to the rear of the unit and two Sovtec 6SL7GT tubes in front. Hmmm. Never been a fan of Chinese tubes versus some good ol' NOS ones, so enter in some new, er, um, old tubes. Replacing the 5AR4 with my old fave Mullard CV1377 (basically a military-grade brown-base 5AR4) helped to lessen that hygienic sound quite a bit. Things were now cookin'. By the way, after taking the top off I noticed the unit uses virtually 100% point-to-point wiring and all tube bases are of the top-quality ceramic variety. Once everything was set, it was time for music. And music it did play!

Call me a basshead, a subterranean dude, a bassaholic. The last thing expected was high-definition bass to really come through. Hey, we're talkin' 3 watts here. How wrong I was! The acoustic bass heard on the wonderful new Sara K. Hobo CD (Chesky Records 9037 155 2 ) as well as Geddy Lee's bass on various Rush recordings were both tight and clean, to a certain volume point. Not only was the bass tonally right, it was amazingly good overall -- full- flavored, impressive, and with proper harmonic structuring too, but without any sense of strain or congestion. Amazing in fact. Even fast bass riffs on my various Rush vinyl/CDs were like the agility of the new McLaren Formula One cars. It ran circles around virtually everything else I have ever bought, begged, or borrowed. The one thing, in general, that separates the men from the boys is how well a unit can decipher intricate lower-frequency passages. In this regard, the Moth did amazingly well. All 3 watts of it. OK, OK. So it's hard to get past the 3-watt thing.

Now, as for the mids, how can I say this and seem sane? Forget sanity; this thing was just freakin' stupidly good for the money. They say the first watt is the most important one in terms of the crucial midrange. The mids weren't seductive or euphonic. Upon playing the aforementioned Sara K CD, I noticed that her voice was supple yet gutsy. When Sara is played on the right system, her voice can be so, um, seductive. Hearing her live was a big highlight for me last year. If you ever get a chance to attend one of her performances, please do so. Now back to the mids and highs. They were very clean and fast -- just like the bass was. There was a touch of hardness in the lower treble that might be due to the Chinese 2A3 tubes used. Unfortunately there weren't any NOS single-plate 2A3 tubes in my stash to substitute. My friends say the single-plate tubes are the best, yet they are quite expensive too. Maybe I'll hit the lottery one day. Hey, my odds are huge at one in a kabillion or so. In the end, the mids were extremely tactful and the Moth s2A3 was unraveling more than every other amplifier I've heard save for the Audio Note Ongaku and another tube unit here that is yet to be reviewed and costs twice the price of the s2A3 (yet it can output 75Wpc).

As for the highs, well, they were very extended, clean, and fresh like early-morning fishing out in the middle of a favorite lake. Ya know, it's good to get a breath of fresh air every now and then. The bass all the way up to the highs also had a great sense of contrast in the dynamics. Unfortunately the very small microdynamics seemed a tad constrained. This is Audio Note Ongaku territory here at $89,200, not at $3,450. Again, this also might be due to the Chinese 2A3 output tubes used.

Unfortunately there are no really great headphones here to try. Personally, I have disdain for headphones. Hated them in the recording studio, hate them in my home. They all seem to make things sound artificial, in my humble opinion. Of course, this could be due to not properly projecting a realistic, real-world soundscape. As an amplifier, the Moth s2A3 did wonderfully well with my personally modified KEF 104/2 speakers, Royal Reference 3As and another diamond-in-the-rough speaker made by Legend Audio and called simply, The Legend.

In closing, the Moth s2A3 was one of the fastest, cleanest, and best "little train that could" my ears have heard for quite a while. The one thing holding some systems back may be the chosen speakers. Fortunately more and more manufacturers from Alón to Wilson and many in between have been making their new products with higher sensitivity. Life is good. If you get a chance to audition the Moth s2A3, may I humbly recommend you drag yourself to do so. Just please remember, it may be only 3Wpc, though in the right system it can easily satisfy the rocker in you too. In the end what really matters to me is that you.... Enjoy the music!

...Steven Rochlin

Moth Audio Corporation s2A3 Amplifier
Price: $3,450 USD

Moth Audio Corporation
1746 Ivar Avenue
Hollywood, CA 90028
Phone: 213-467-4300
Fax: 213-464-9100

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