Power Amplifier Air Tight ATM-1E

Air Tight ATM-1 (2024 Edition) – a valve push-pull amplifier with EL-34 valves in an ultralinear configuration

The ATM-1 (2024 Edition) is a stereo push-pull valve power amplifier featuring EL-34 output valves, which builds on the original model from 1986 and arrives eighteen years after the last update. The design is conceived as a tool for listening to music: the priority is tonal balance, operational stability and utilising the characteristic properties of the EL-34, rather than circuit experiments for their own sake. The declared output power is 35 W + 35 W per channel, which corresponds to the typical operating mode of this valve.

The signal path is based on a tried-and-tested Leak-Mullard circuit configuration with an ultralinear (UL) output stage, which strikes a balance between the linearity of triode mode and the power reserve of a pentode configuration. The magnetic components – the output transformers and the Tamura choke – are among the key elements determining the transfer characteristics. The operating point of the output tubes is controlled by a fixed-bias circuit supplemented by a vertical analogue meter, which allows for precise and repeatable adjustment of the quiescent current without the need for external instruments.

The mechanical design meets the requirements for resonance suppression. The internal assembly and cabling are routed on a sub-chassis made of pure copper and carried out by hand by Air Tight technicians. The monocoque main chassis minimises the transmission of vibrations to the valves and transformers; the base plate is made of steel plated with polished copper, and the front panel consists of a thick aluminium die-casting with no visible screws. The lower level of mechanical vibration in these microphonically sensitive valves results in a quieter background to the recording and stable localisation of instruments within the stereo image.

Connection to the source is provided via a standard RCA input; an unbalanced XLR version is also available as an option. The speaker terminals are rated for impedances of 4 Ω and 8 Ω, and 16 Ω on request, which allows for more precise adaptation of the output transformer to the actual impedance characteristics of the loudspeaker system and contributes to better bass attenuation. The compact dimensions, whilst maintaining mechanical strength, emphasise the slim silhouette of the EL-34 tubes.

Key features

• Power: Push-pull EL-34 with 35 W + 35 W output
• Circuit: Leak-Mullard configuration with ultralinear wiring
• Transformers: Tamura output transformers and choke
• Bias: Fixed bias with vertical analogue meter
• Construction: Monocoque chassis and copper sub-chassis wiring
• Connectivity: RCA input, 4 Ω and 8 Ω outputs