Power Amplifier Air Tight ATM-2Plus

Air Tight ATM-2Plus – a push-pull stereo valve power amplifier featuring KT-88 valves

The ATM-2Plus is a stereo push-pull valve power amplifier featuring KT-88 output valves, building on the ATM-2 model from 1988, which has been in production for more than three decades. The ‘Plus’ version features a complete redesign of the internal circuitry whilst retaining the brand’s original aesthetic. The aim of the redesign was to redefine the capabilities of the KT-88 valve, with an emphasis on operational stability, valve lifespan and compatibility with modern loudspeaker systems.

In the driver stage, the original 12AU7 tubes have been replaced with more powerful 6CG7/6FQ7 tubes, which provide a wider amplitude with lower distortion. Optimised negative feedback (NFB) adjusts the damping factor to match the characteristics of modern transducers. The signal path is routed via point-to-point wiring without printed circuit boards in the traditional Air Tight monocoque construction; the connecting hardware is concealed using stud-boss technology, which contributes to more thorough chassis earthing. The amplifier is hand-built at the factory in Takatsuki, near Osaka.

The power supply and output sections comprise oversized 100 W Tamura output transformers and a bespoke, hand-wound mains transformer with paper insulation. The headroom provided by the output transformers is evident in the control and fullness of the bass range, even under more demanding impedance loads, whilst the oversized power supply reduces power supply voltage modulation and promotes a more stable, spatially wider soundstage with more precise instrument localisation.

Operational reliability is enhanced by a reduced anode voltage, which extends the service life of the KT-88/6550 valves without any significant loss of power, and by fast-acting fuses that protect the circuits in the event of valve failure. The combination of a more moderate operating mode and a robust power supply results in low noise levels and consistent performance during extended listening sessions.

Key features

• Circuitry: Push-pull output stage with KT-88 tubes
• Driver stage: 6CG7/6FQ7 tubes with lower distortion
• Transformers: Oversized 100 W Tamura output transformers
• Power supply: Hand-wound mains transformer with paper insulation
• Construction: Monocoque and point-to-point wiring without printed circuit boards