Усилители мощности стерео — Air Tight ATM-1

The ATM-1 is the stereo EL34 power amplifier that started the Air Tight catalogue, first launched in 1986 by A&M Limited of Japan. An ATM-1S version followed in 2006, and in 2024 the company released a new edition, also listed as the ATM-1E, which is the first update of its EL34 amplifier line in 18 years. The maker describes the goal of this edition as authenticity over novelty and balance over uniqueness, keeping the character of the original while using current parts.

Key specs that matter

Rated output is 35 W per channel at 1 kHz with THD below 5 percent, and the same figure is given for 4 ohm and 8 ohm loads. Frequency response runs from 20 Hz to 30 kHz within minus 1 dB, measured at 30 W. Input impedance is 100 kohm and input sensitivity 700 mV for full output. The damping factor is 6.7, measured at 1 kHz and 1 W. Power consumption is 250 VA. The chassis measures 365 mm wide, 305 mm deep and 225 mm high, and the amplifier weighs 21.5 kg.

Engineering and use context

Tubes fitted are one 12AT7 (ECC81), two 6CG7 (6FQ7) and four EL34 output pentodes, two per channel in push-pull. Air Tight uses a Leak-Mullard type circuit, and the EL34s are ultralinear-connected, a choice the company made to balance quality against the aim of drawing stable output from each channel. Output transformers and the choke coil come from Tamura. Bias is fixed and set by the owner with the help of a custom precision vertical edgewise meter on the chassis. Parts are chosen through listening checks and are mounted and hand-wired on a pure copper sub-chassis. One pair of RCA sockets forms the standard input, which can be converted to XLR on request, though the connection stays unbalanced. A 16 ohm speaker tap is available as a factory option. The earlier ATM-1 used a pair of 5AR4 rectifier valves and manual biasing, while the ATM-1S moved to solid-state rectification and user-adjustable bias.

Pairing

With its low damping factor, this amplifier's source impedance interacts with the load, so speakers whose impedance stays fairly flat are a safer match than multi-way designs whose curve drops sharply in the bass. The input sensitivity is within reach of nearly every line-level preamplifier. Owners of higher-impedance vintage or horn speakers should order the extra tap so the EL34 stage sees its intended load.

Alternatives

The Air Tight ATM-300R is a stereo single-ended design by the same company using 300B triodes and rated at 9 W per channel.