Nestorovic Labs Alpha-1

the Alpha-1 defies conventional labels in most respects. First of all, it's a tube amp that actually looks good without looking gaudy. Its mirrored-chrome chassis and black cover are a striking contrast to other large tube amps, most of which look like stage props for a Buck Rogers movie. Even with the lights off, the Alpha-1 looks attractive, with its rear-illuminated name-plate and soft glow of the tubes visible through the cage.

The Alpha-1 runs as a balanced output amp its outputs consist of hot and inverted-hot terminals, as opposed to the conventional hot and ground connections. This significantly improves the efficiency of the power supply (one of the greatest weaknesses in most tube designs) and, if the output stage and power supply can handle the doubled current demand, will quadruple the rated output power compared with a single-ended design running off the same B+ rail. But the unique feature of the Alpha-1 for a domestic tube amplifier is its ability to run a balanced differential input. Admittedly, this is a feature of which few users will be able to take advantage, since most preamps, even those with a phase-inversion switch, do not offer a second pair of inverted outputs. But it does make a noticeable difference to the sound.

A feature of the Alpha-1 unique in these modern times is a feedback adjustment switch on the rear, which allows the level of feedback to be adjusted between "normal" and "low." Although the manufacturer does not publish specifications for the amount of feedback present at either setting, I assume the quoted distortion specifications are in the "normal" feedback mode. The performance of the Alpha-1 was clearly better with the switch in this position. In the low feedback mode, the amp sounded slower, with a distinct loss of detail, particularly from the midrange on up.

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Vacuum tube mono power amplifier.
Rated power output: 150W (8 and 4 ohms, 21.76dBW and 18.76dBW).
Frequency response: 20Hz - 20kHz, +0, -0.5dB.
Input sensitivity: 2V balanced, 2V unbalanced for rated output.
Input impedance: 220k ohms.
Weight: 27.3kg.