Усилители мощности моно — Lamm Industries M1.2 Reference

The M1.2 Reference is a hybrid mono power amplifier designed by Vladimir Lamm for his New York firm. It represents the top of Lamm's hybrid and solid-state line, combining a single valve in the driver stage with a MOSFET output stage running in pure Class A. It is sold as a pair of units, one per channel.

Key specs that matter

Output is 110 W in Class A into 8 or 4 ohms, with switch-selectable bias and voltage settings for each load. Input impedance is 41 kohm on balanced and single-ended inputs, and output impedance is 0.082 ohms. Frequency response is 4 Hz to 155 kHz (+0/-3 dB), slew rate is 33.5 V per microsecond and damping factor is 98 at 8 ohms. Each chassis measures about 210 x 430 x 570 mm including handles and weighs 31 kg.

Engineering and use context

The signal enters through RCA or XLR inputs and passes to two high-speed buffers originally designed for video applications. These drive a differential cascode stage of matched J-FET pairs feeding matched PNP transistors. The cascode feeds a single 6922/ECC88 double triode, which drives a single-ended stage of two NPN transistors, one acting as a powerful current source. A small amount of feedback, 6 to 7 dB, runs from the driver stage to the input, but there is no overall loop feedback around the output stage. The driver stage couples capacitively to six pairs of fast MOSFETs in the output stage, all running in Class A. Because Class A output transistors conduct continuously, they never switch off during the signal cycle, avoiding crossover distortion, at the cost of high heat and power draw. The bias switch sets the operating point to match an 8 ohm or 4 ohm speaker, so the amplifier delivers its full Class A power into either. Power consumption is typically 330 W, at idle as at rated output, since the output stage draws full Class A current all the time. Short-circuit protection is built in. Front and rear handles make the chassis easier to move. Lamm's approach mixes technologies deliberately, using transistors where they bring speed and current and a valve where he favours its behaviour in the voltage gain stage.

Pairing

With its switchable bias, the M1.2 Reference suits speakers of 86 dB and above with 4 or 8 ohm loads. Lamm's L2.1 Reference preamplifier includes remote on and off for Lamm amplifiers.

Alternatives

Lamm Industries' ML2.2 is the single-ended valve mono amplifier of the range for high-sensitivity speakers.