Discover the EL-34 Air Tight ATM-1 Valve Power Amplifier
One amplifier which came my way in 2021 was the AirTight ATM-1. This was a remarkable little amplifier which made a big impression as part of the Tannoyista system.
Air Tight had always been one of the manufacturers which I heard of but, alas, never found the time to take a look at. So when an ATM-1 came along, I thought, why not...
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My go-to amplifier at the time was the wonderful KT-150 valve-based Tube Distinctions Copper amplifier, a wonderful-sounding piece of kit. Of course, the Air-Tight wasn't in the same league as the Copper, but still, I was surprised by the sound of the ATM-1.
The ATM-1S has now succeeded the ATM-1 but it had a great run since 1986 until 2010. And now Air-Tight's model range extends even further. So this 'classic' little amplifier was a nice insight into the Air-Tight sound.
The ATM-1 is a 36w push-pull amplifier with a unique CD direct input control. So on the front panel, we have two RCA direct inputs. An input selector which allows you to select the front or rear RCA inputs. And two attenuator controls for both L & R channels. Attenuator controls on a power amp? Well, in this case, yes. Passive? Maybe. These controls can be handy for source equipment with a high output so you can adjust it accordingly. Or, this power amplifier can be used as an integrated. Handy for some I suppose but to me, a little odd. Especially when they made a matching preamp too!
Its successor, the ATM-1S has the same controls but with some differences. The 'S' stands for 'Special'. The main difference of the Special version is that you lose the valve 5AR4 rectifier valves as it uses transistorised rectification and a user-adjustable biasing system.
How does the ATM-1 sound
The ATM-1 with 36wpc in Push-Pull should match my 15" Tannoy Monitor Gold loudspeakers (LINK) quite well, so hooking them up along with my Croft preamplifier, we're ready to go.
I set the volume controls on the amplifier to around halfway at first before opening them up to full.
Starting with vinyl, I thought I'd start by playing something gentle and Tales of Us by Goldfrapp was my first choice. The first thing I noticed was the amount of air in the sound and how full it was. The detail retrieval was quite surprising as it was almost immediately noticeable that the mid-range for Alison Goldfrapps's vocals was quite lush. Whilst the bass wasn't as prominently voluptuous as I was accustomed to, the first full play of the album started to give me a signature to this compact amplifier.
I carried on with something more modern and a favourite of mine, The Wonder Stuff, Never Loved Elvis. This album has lots going on, but it's not as articulate as the previous album which goes for many albums recorded in the 1990s. But still, the swirl of the music came through, the speed of the delivery was very nicely done, and, although the more complicated cymbal splashes weren't disappointing, they weren't quite as smooth as I wished for.
My next choices were a mix of both vinyl and digital including Leftfield, Seal, Curtis Mayfield, Spiritualized, Lou Reed and after a few days, I found what this amplifier really liked and what it had in common with. I found classical was probably its main love together with 60s/70s rock was where it's at, which is very cool as I love the psychedelic rock era.
But for me, something more modern, bass-heavy, dance or some DUB, the cracks started to show. One thing that did impress me was that it was very articulate at lower volumes, but by giving it something with more energy at a reasonable volume, I found that the sound became a little flat but not enough to not be addicted to its charms.
It seemed that the ATM-1 didn't seem to have enough grip for the 15" Tannoys, even though they're quite sensitive. This is something I've found before with other amplifiers, for example, the QUAD II's. Generally, anything under 50wpc with 15" Tannoys just doesn't get the best out of them. So nothing is notably wrong or different there in regards to this amplifier.
The build quality of the ATM-1
Let's look at the build. From first impressions, it's a very compact and solid amplifier.
Weighing in, this little compact amplifier weighs in at 22kgs. The main chassis is made from mild steel and coated in a very nice charcoal grey. A very nice finish, whilst underneath, a nice copper-coated polished steel panel. The main faceplate is nicely machined and the control knobs are a nice quality too.
The action of the selector is nice as are the volume controls. All controls are made by Alps which is nice to see. The quality of the RCA sockets are also of decent quality as are the binding posts.
Although I don't know about the power transformer, I can only assume it's of great quality just like the Tamura Seisakusho output transformers.
Conclusion
The Airtight ATM-1 is an old amplifier and I wouldn't expect nirvana. It was from a different era. But in many ways, it did deliver just that. Its ability to reproduce the most gentle and dynamic music is as good as anything I have heard.
The build quality is superb and if you manage to find one of these amplifiers, like myself, make sure you have it serviced and biased before making your mind up.
What did I love?... Detail and the midrange presence, bass on gentle recordings were sublime. A romanticised delicacy and speed on slower tracks. Low-volume bass.
What didn't I love?... Not enough grunt and grip for anything complex at volume. Timing and accuracy on more complex tracks. Not easy to bias. The volume controls are not required. Front-facing RCA sockets are ugly.
What could be done?... Apart from the aesthetic functions, I'm absolutely sure that the ATM-1 can be upgraded massively today. It needs to be less shy and cuddly, more grunt and speed for my liking. And adding an auto-biasing system would also be a great thing to do. And for those reasons, I think the ATM-1 is something of a bargain on the 2nd hand market.
Specifications
The ATM-1 circuit is a Mullard NFB type circuit using 5AR4 and EL34 valves as well as the 6CA7, ECC82 and ECC83 valves.
| Type | Stereo power amplifier |
| Effective power | 36W + 36W (8 Ω) |
| Total harmonic distortion factor | 0.1% or Less (1 kHz, 1W) 1.0% or Less (1 kHz, 36W) |
| Frequency characteristic | 20 Hz ~ 20 kHz ± 1 dB (36W) |
| Input sensitivity | 1V |
| Impedance | 100k Ω |
| Signal-to-noise ratio | 100 dB (IHF-A, input short) |
| Load impedance | 4 Ω, 8 Ω |
| Vacuum tube used | 6CA7x4 12AU7x2 12AX7x1 5AR4x2 |
| Accessory function | Input 2-system switching SW |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Power consumption | Approx. 250W (Electrical Appliance and Material Control Law) |
| External dimensions | Width 368x Height 298x Depth 231 mm |
| Weight | 22kg |
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