Review: Air Tight ATM-3 Tube amp

Category: Amplifiers

Air-Tight ATM-3 Mono Block Triode Amplifiers
When I came home and saw the Air-Tight ATM-3's two boxes, their size and weight surprised me. These were as big as my Plinius SA-102 boxes with a weight of 55 lbs. I unpacked the amps and set them on the floor. They started building the ATM-3 in 1991 with an original price of $ 12,800. They have now stopped them and can be found used for around $ 4000-4500.
My first impression was they were just like the tube amps from the sixties. A brushed aluminum face plate, a couple buttons and a meter were all that graced the surface. Behind the face plate are (6) 6CA7 output tubes, (1) 12AX7 and (1) 12AU7, enclosed in a thin, inferior feeling black steel casing with holes for ventilation. I wondered if the thin metal could add some noise (ringing) to the tubes through vibration. I am left wondering why they still use this type of enclosure. They rated the output at 55W Triode and 110W Pentode. They provide a selector switch to choose between the two modes of operation. I used the Triode mode for my audition. The back side of each amp has a single RCA input and two screw type speaker binding posts. The hole in the post is not large enough to accept my banana fittings, so I had to find my WTB spades to adapt the speaker cables. To my disappointment only a fixed power cord is available, precluding one of my preferred tuning tweaks.
After setting the amps on the Neuance shelves used by my two Plinius SA-102 amps I connecting them into the system. After letting them warm up for about four hours before my first listen. My initial impressions were mixed, overall the sound was smooth, good deep base, great depth but lacking in PraT and detail compared with what I am familiar. I left the amps running for the next two weeks before any critical listening. I started my evaluation with a few well-known current favorites, Dead Can Dance "Into the Labyrinth," Patricia Barber's new "Verse," Kasey Chambers "Barricades and Brickwalls," Lucinda Williams "Car Wheels on a Gravel Road," Nora Jones "Come Away With Me," Patricia Barber "Modern Cool" SACD, Alison Kraus "New Favorites" SACD, Duke Ellington "Blues in Orbit" SACD, and "Natures Realm" Philadelphia Orchestra SACD.
They impressed me with their depth and power in the bass. Not quite as tight as the Plinius nor do they provide the same degree of texture. However, they had all the power and punch to which I am familiar. The midrange was as smooth, liquid and effortless as any amp I have heard. This could be a great thing with certain set-ups, but for me it became problematic. Patricia Barber's voice was gorgeous, as rich and smooth as imaginable. I have seen Patricia often in person, and her voice is simply not this liquid. Her voice is dark and biting, like a strong cup of coffee. The Air-Tights made it a thick chocolate with a smooth creamy caramel. If I had never heard Patricia on my system or in person, I would say this was great, but as it was it is simply not real. Two of my favorite women, Kasey Chambers and Lucinda Williams and the male voice on Dead Can Dance has a lot in common in their vocal style. They have a great deal of grain and texture in their voices, filled with expression and emotion. I enjoy these singers because I can feel their souls, they extend their raw emotion through their raspy, throaty voices. An infinite palate of color, texture and sensation is expressed through their voices, giving me a window into their souls. The Air-Tight simply glosses over all of this, and they are not able to delineate this fine level of detail. Again had I not heard these women in person, and through my system, I would be running around praising their smooth liquid voices. The problem is smooth and liquid would never be the way one would describe a live performance from either one of them. On Patricia Barber's "Verse" and "Modern Cool" and Duke Ellington's "Blues in Orbit" there are passages of trumpets. In real life and with my system the trumpet is biting, brassy and harsh. The Air-Tights made them warm, smooth and harmonious. Although the treble on the amps is closer to natural, they still were a bit edgy at the very top. This was the type of energy that makes your ears ring a bit, but not so much that it was offensive. Removing the metal back improved this some, but it remained an annoyance. I am sure cables and footers could solve this issue with the proper diligence. The depth of the presentation was impressive but very different from my system and it took me awhile to get a grip on it. My system puts the front/ middle performer about 5' behind the speaker plane, and with a small ensemble the stage is 10-15 feet deep. With the Air-Tights the front was 10-15 feet back and the back of the stage was at least 50' away. The rear performer would often change positions based on who played the lowest note. If the drum were lower than the bass player, the drummer was in back. If the bass player was lower, he became the back player. This was not overly noticeable, but once I saw it I became obsessed with it. The most serious issue for me was the PraT (Pace, Rhythm and Tempo). Plinius are an extremely fast amp and they have an energy that brings excitement and life to the music. The Air-Tight's were unable to keep pace (so to speak) They were simply unable to produce the life and energy I am familiar. I found myself uninterested in music I love and enjoy on a continuing basis.
So overall, with my system these amps left disappointed me. Now consider that my system consists of Dunlavy IVa speakers, large full-bodied speakers. I believe these may not be the best fit for tube equipment. My impression was with a different speaker the whole picture might change. If for instance I had tried Martin Logan or Megapan with their great transparency and speed, or a tighter cone speaker like Meridian or Theil, I might expect to hear better performance. This is strictly a guess on my part. I already use one of the quickest and most transparent cables (Valhalla) and pre-amp (Placette), leaving the question of how a speaker would alter this annoyance as strict conjecture.
For my tastes, this amp is simply not to the standard of other amps within this price range. If however your looking for the smooth, liquid, colored experience, I would test them out. When I went back to my Plinius amps, it took no time for me to settle back in. I missed my Plinius while this three-week period was happening, I am happy to be back!
My experience with these amps (and matching AT preamp) in a system featuring SoundLab Dynastats - obviously a very different speaker - was pretty similar to yours. I did not like the sound of that system from a standpoint of overt tonal coloration (highs rolled, mids bloated and uneven, bass a day late and a dollar short) and lack of liveliness, although it did have great imaging and scale. But I can't put those complaints on the amps alone, since the speakers and overall system synergy/set-up surely played a part (I will say that the quality of the sources - Goldmund/Clearaudio analog, Accuphase digital - plus Nordost SPM/Quattro Fil cabling, seemed beyond reproach). I still gave the amps the benefit of the doubt with that audition, especially since I knew the speaker set-up was done hastily.

But what was clear in that audition was that between the two modes, triode was not the way to go if you wanted to hear some (relative) clarity, control, and extension, at least with those speakers. Running the EL-34 output tubes in normal tetrode mode yielded more acceptable results to me, and the system's owner agreed as well. Other than the issue of you basically listening only in triode so it seems, did you ascertain that the tubes were still up to snuff? Oh well, these aren't ever going to sound like your Pliniuses anyway, but I guess that was the point. But you've made it clear how you feel about your reference amp before, so what were you looking for this time around?
Excellent review. Comparing the sound to the live experience is absolutely appropriate (unless the recording engineers tweaked too much) and I applaud you for it. Too bad more reviews, especially in the press, don't do this!
Jadem6: An excellent and well documented report, as usual! Incidentally, I am supposed to try out used ATM-3's next week (not for purchase; just as try-out). My experience, if it takes place, will be different -- the amps will drive the upper part of the speakers (over 84 Hz).
I think your use of the Placette might have been responsible for some of the sounds you heard. The input impedance of the Air Tight must be considered, as well as the gain setting you used via the attenuator pots. Finally, while the air tights have a decent power output, pairing them with a Dunlavy would not be my choice, particularly in triode mode.

I've heard these amps on several systems (I used to sell them), and the preamp choice is critical. I've got a pair finally of my own, on their way as I type, and to be paired with Air Tights ATC3. I'll have to play with them for a while, but my prior experiences are very positive.
What Davehg said... Dunlavy IVas spec a minimum power requirement of 50 watts. IMO, the ATM-3's 55 watt output in triode mode is simply insufficient to drive the Dunlavys for critical analysis. I should know, I have a pair of ATM-3s and used them to drive Thiel CS6's and now CS7.2s.

I concur with Jadem6's impression listening in triode mode trying to drive huge speakers - it sounds like ass. Listening in Ultralinear mode (Tetrode) is an entirely different experience.

I have the matching ATC-2 Preamp so impedance matching is not an issue in my system. The ATM-3's have plenty of punch to drive the Theil CS7.2s to realistic concert levels without running out of steam. Listening to acoustic jazz, my personal favorite, is a real treat. I haven't heard Patricia Barber in person but her voice is hardly smoothed over on my system. Both male and female vocals are very realistic and bass response is deep, tight and quick.

Check out my entire system in Member Systems titled "Integrated two channel/Home Theater System"
Having listened to my ATM3's for a few months, now, a couple of thoughts. Mine have the Tom Tutay mods which include better binding posts, a soft start circuit (to save the tubes from too much start up juice), and IEC connector allowing me to use any PC I want (currently Cardas Golden Ref).

First, Triode still sounds more real than Ultra Linear, but the differences are close except in the presence area, where nothing beats triode.

Second, I was using an AirTight ATC3, which I think is all wrong for this amp. It sounded better with the source running directly into the amp. I swapped for an Aesthetix Calypso, which has proved to make all the difference. With the Air Tight ATC3, glassy tube glare and limited air. With the Aesthetix, simply magic. This leads me to second my prior comments: I think passive preamps just don't work with this amp.
Hi Jadem6
I live in New Zealand where Plinius is made and have owned several Plinius amplifiers personally, the Class A 50 watt and Class A 100 watt amplifiers being their best amplifiers in my personal opinion.
Live is the reference point to all music, but you have to also realize that live music play back today is most of time played back through big PA rigs using solid state amplifiers.
If you plugged one of these PA amplifiers into your home speakers with out all the mixing desk adjustments you might have a different opinion on the sound quality.
You are right in the opinion matching amplifiers to speakers is the best way to get musical system synergy.
I have built my own preamplifier & power amplifiers to match my own Horn speakers, this system is placed in a dedicated acoustically treated listening room.
The best solid state amplifiers I have used in this system is the Pass Labs XA 100.5 Class A amplifiers, these amplifiers provide wonderful sound.
If you use a speaker that would match the 55 watt triode output of the Air Tight ATM 3 mono blocks with the Air Tight ATC-2 preamplifier your would be very impressed.
System synergy is is very important to get a great sound, room interaction is 40% of the sound quality.
In the domestic field of music playback we do not usually have the luxury of mixing the sound playback to each listening room, so then room acoustic treatments are a necessary part of the sound system for best sonic results.
I think in your system the Plinius might just be a better match to your loudspeakers resulting in your findings of your review.
Try the Plinius amplifier on a pair of Avantgarde horn speakers or PHY based speakers then compare the sound to a Triode valve amplifier on the same speaker, now you might have a different opinion of the Plinius amplifier.

Thanks Jason.