Power Amplifier Air Tight ATM-2211

Air Tight ATM-2211: a monoblock SET amplifier with a directly heated 211 triode

The ATM-2211 is a monoblock valve amplifier in a Single-Ended Triode configuration with a 211 power valve, launched to mark the 35th anniversary of the Air Tight brand. Instead of the usual overall negative feedback taken from the output transformer, it employs deep feedback from the anode of the 211 valve to the first stage. This signal path prioritises energy and impact in the sound reproduction over more formally favourable specifications, whilst delivering 32 W of output power without compromising transparency or dynamic range.

Operational reliability is based on fixed bias and DC filament heating with precisely defined operating points for each stage. The power supply circuit utilises separate transformers for high and low voltage; filtration is complemented by a hand-wound choke without a traditional core, crafted by Japanese master craftsmen with an emphasis on high-voltage resistance. A vertical analogue meter allows for continuous monitoring and precise adjustment of the quiescent current.

Signal transmission to the loudspeakers is handled by Hashimoto Electric output transformers, which extend and reinforce the response in the lowest frequency range. Mechanical stability is ensured by the Air Tight monocoque chassis, which suppresses resonances; the main circuit boards and capacitors are mounted on a pure copper sub-chassis isolated from the main frame, whilst the front panel is milled from a solid block of aluminium. The rigid construction, combined with high-quality filtering, reduces signal modulation caused by vibrations, resulting in stable instrument localisation and clarity in quiet passages.

Speaker connections are handled by WBT terminals with separate terminals for 4 Ω and 8 Ω; optional RCA and XLR connectors are available on the input. A circuit with a time relay ensures a gradual build-up of the anode voltage, thereby protecting the valves from current surges and extending the service life of the capacitors.

Key features

• Circuit configuration: Single-Ended Triode with a 211 tube, 32 W
• Feedback: Deep anode feedback instead of global NFB
• Power supply: Separate transformers and hand-wound choke
• Transformers: Hashimoto output transformers for tight bass
• Construction: Monocoque with copper-sprung sub-chassis
• Connectivity: WBT 4/8 Ω terminals, RCA and XLR inputs