Nestorovic Alpha-1 power amplifier

The great debate that has long separated audiophiles is tubes vs solid-state. Other topics, CD for example, may temporarily steal the spotlight, but year-in and year-out no other subject is the cause of as much controversy as whether tubed or solid-state circuitry produces the more accurate sound. As is typical with long-standing feuds, the split runs deep, and tempers often flare.

Even if you are among the majority of audiophiles who keep open minds in this matter, making a decision between tube and solid-state electronics is one of the most difficult choices you can face. Each technology has its advantages and weaknesses—there is no one right choice. Picking either means sacrificing the virtues of the other.

Mile Nestorovic, designer of much of the now-legendary McIntosh tube gear, is a hero of sorts among tube lovers, but he has always managed to stay clear of—perhaps "above" would be a more appropriate word—the tube vs transistor dispute. It is appropriate, then, that the first amplifier to bear the Nestorovic name transcends the expected sonic distinction between tube and solid-state to produce a sound that defies conventional labels.

In fact, 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.

The Sound
I used a Klyne SK-5 preamplifier with the Alpha-1, which was convenient because the SK-5 does have two pairs of outputs inverted in phase relative to each other, allowing me to audition the amplifier in both balanced differential and conventional input modes. Using the single-ended input produced a respectable but unextraordinary sound with, apart from good low-bass performance, a distinctly tube-like character. All in all, a good amplifier, but not the most cost-effective way of spending nearly five kilobucks. Running the inputs in balanced mode, however, brings the Alpha-1 to life. The sound improves markedly, and the tube character disappears. Since it is my belief that a component should be reviewed at its best, the remainder of my comments on the Alpha-1 assume the use of the balanced inputs and the "normal" feedback setting.

Overall, the Alpha-1 sounds clean and well-balanced, though just a touch warm in the lower midrange. The midrange is very transparent and detailed, but not as fast as some of the best solid-state amps. Harmonic contrasts and detail are rendered as well as I've heard from any amp. The tonal characteristics of different woodwinds come through with exceptional accuracy, and there is no trace of grain or harshness in the violins.

The treble also is free from grain and hardness, and has excellent detail. Although the HF is well-extended for a tube design, the Alpha-1 cannot match the HF extension of certain solid-state amps, such as my reference BEL. Still, the Alpha-1 is sufficiently well-extended for believable reproduction of anything found in music, and is as open and clean at the top end as any. Most important, the Alpha-1 has the transparency, air, and subtlety in revealing detail in the lower to mid treble that is the hallmark of the better tube amps. As a result, vibes, chimes, and other sounds with delicate upper harmonics are remarkably lifelike. I've heard few amps that can equal the Alpha-1 in the lower to mid treble.

The bass is excellent for a tube amp, being tight, reasonably quick, and not nearly as bloated in the mid to upper bass as most tube designs. In fact, the bass is far more characteristic of a good solid-state amp than of an amplifier using tubes (and their necessary output transformers). The midbass is slightly warm, and performance does drop off noticeably in the bottom octave, below 32Hz. This latter condition is undoubtedly due to the current delivery limitations inherent in tube designs.

The image is wide with good depth, but not as holographic as I have heard from some tube amps. That is, the illusion of a real body present in the physical space of the listening room—one phenomenon where I've always felt tubes have the upper hand—doesn't come through as well as I had hoped. On the other hand, the Alpha-1 does exceptionally well—better than most tube or solid-state amps—at such things as separating massed instruments, particularly strings and voices, and in giving a sense of height to the soundstage that allows one to quickly tell the microphone perspective used in the recording.

Transients are quick and dynamic, and there is a sense of more than ample power. Even more important, the relative dynamics of various instruments (on properly made recordings) are accurately preserved.

Because of its rather hefty price tag, I've been fairly critical in evaluating the Alpha-1; but despite my best efforts to fault it, it still comes out quite well. It manages to preserve most of the virtues of tubes while minimizing the extent of their traditional weaknesses. The overall character of the Alpha-1 is closer to a top-notch solid-state design than to a tube amplifier, and I don't think, therefore, that it will appeal to someone who enjoys traditional tube sound. I've always used solid-state amps as my reference because of their superior performance at the frequency extremes, and because of the excessive colorations present (in my view) in most tube amps. Far from suffering at the frequency extremes and in neutrality, the Alpha-1 is exceeded in these areas only by the best solid-state products. And it offers many of the virtues of tubes that I've always wanted in my solid-state amps.

While there is no one amp that is right for all systems and tastes, the Alpha-1 is one of a very small handful of amps, and the only tube amp, that I would consider for my personal use. My one hesitation in recommending it is the need for a preamp capable of driving a balanced input in order to realize optimum performance. Run with a single-ended input, its performance is unremarkable for its price; if you can use it balanced, the Alpha-1 is highly recommended.

Nestorovic Labs
Company no longer in existence (2018)