Infinity HCA power amplifier

Imagine if you can a power amplifier with the bass richness, midrange liquidity, and high-end accuracy of the best tube amplifiers, and the inner detail, transient attack, and bass solidity and range of the best solid-state amplifiers. If you can imagine that, you can visualize what this amplifier sounds like.

There are some amplifier designs around in which transistors are used throughout until the output stages, which are tubes. This defies explanation, for among listeners who can recognize merit in the "tube sound," it is generally acknowledged that tubes do best in early stages and transistors are the best output devices. This is the first power amplifier that has followed that principle. In the HCA, all stages except the outputs use tubes, with high-speed circuitry achieving high-frequency response into the 0.6MHz region—far surpassing any previous tube designs in audio. The output stages use 12 power transistors, operated in class-A mode for minimum possible distortion.

The HCA uses industrial-grade tubes which are normally guaranteed for 10,000 hours of use—implying a stable-condition tube life of around 8000 hours. At two hours a day, this works out to a little over 11 years of undiminished operation—hardly a cause for concern. As in the case of the Berning preamp reviewed in this issue, the manufacturer here assures us that these tubes—unlike those which were intended for the consumer market, such as the 12AX7—should continue to be readily available for a number of years, since they are used in military hardware that would cost far more to replace with solid-state (with no gain in performance) equipment than to re-tube periodically.

It has an effective protective circuit that automatically throws the unit into Standby mode if hit with a potentially damaging overload. It must be re-set manually by depressing a front-panel switch (which can also select the Standby mode if desired, so that one can unplug signal cables without eliciting squawks).

Sound Quality
Sonically, the amplifier almost defies description. With suitable program material and speakers capable of revealing what's going on, it is unequalled in its reproduction of massed-string tone and brushed cymbals—two of the most difficult musical sounds to reproduce. Its low end is awesomely deep and solid, yet without the dryness that we have observed in practically every solid-state power amplifier. It is entirely free from sonic texture, it reproduces depth and ambience superbly, and it is the only amplifier we have ever heard that is at once both detailed and euphonic. And an added bonus is that, despite its remarkable transient capabilities, it exaggerates disc surface noise less than any amplifier of comparable bandwidth.

In comparison with what is probably the best solid-state power amplifier (the Audio Research D-110), the HCA is slightly warmer and more liquid through the middle range, equally open at the high end but without the D-110's slight dryness, and somewhat richer but equally solid and deep at the bottom. The difference is not astounding, but neither is it negligible. Whether it makes the HCA worth about twice the price of the D-110 is a matter that only the buyer can decide. The D-110 is a very musical solid-state amplifier, but the HCA can make musical sounds come to life with almost startling realism.

In comparison with our previous favorite amplifier—the discontinued Audio Research D-150—the HCA produces much fuller, deeper, yet equally well-defined bass, and a much more open high end with less texture (the D-150, by comparison, sounds slightly grainy) and sharper transient attack but a smoother, more natural top. The D-150 is somewhat brighter than the HCA, and also somewhat warmer and "rounder"-sounding. The D-150 can sound gorgeously musical and listenable with the right speaker system (FMI Premiers, for example), but the HCA is almost certainly the more accurate of the two, with the capability for producing (again with the right speakers) the best sonic replication of any power amplifier currently available. In other words, this is now the top power amplifier. For the price, it ruddy-well ought to be!

Unfortunately...
It does have a couple of drawbacks, of which price is obviously one. Few audiophiles are going to be able to afford an amplifier costing $4000, although there is better justification for buying it than for buying any $2000 competitors: It is not likely to be surpassed within a year or so, and it is so good now that there is not enough room for improvement to really justify replacing it with another.

Secondly, it is not suitable for driving most electrostatic speaker systems. While it has the power capability to drive virtually any dynamic speaker system to room-shaking volume levels (and cleanly), it cannot deliver the voltage needed by typically low- efficiency electrostatics.

Thirdly, the Infinity hybrid is noisy. Not electrically—it is dead-quiet through even the most efficient speaker—but mechanically. The class-A output stages tend to run very hot, and a potent cooling system is needed to prevent them from burning up. Nevertheless, we encountered an inadequacy in the cooling system of our first sample HCA, which persisted in going into thermal- overload shut-down after a couple of hours of operation. This, it turned out, was related to the thin air in altitudinous Santa Fe (7000 ft), whose reduced density impairs its ability to draw off heat. The problem, which would have been encountered by any buyer living at a high altitude, appears now to have been solved, for it has not recurred in two months of hot-weather operation.

The fan noise, which measures 51dBA from a distance of 1 foot and 42dBA from 6 feet, is predominantly 300Hz energy, and comes from the forced-air cooling system. The noise is minimized by orienting the amplifier so that its rear faces away from the listening area and, better still, placing it near the speakers rather than near the listening area, but at best it is just slightly higher than the background noise on the average disc at moderately high listening level.

Ideally, the amplifier should be relegated to an adjoining room, or should be housed in a "blimp" similar to what is used to deaden the noise of professional cine cameras when filming with synchronized sound. The only saving grace here is that the noise is unobtrusive enough for most listeners to readily ignore. And as far as we're concerned, it is a small price to pay for such remarkable sound quality.

Conclusion
This, then, is the amplifier for other designers to emulate, with the hope that someone may be able to equal its performance at a rather more affordable price. As for us, we have no intention of parting with this, even if we have to negotiate a second mortgage to swing it.

COMPANY INFO
Infinity Systems
250 Crossways Park Drive
Woodbury, NY 11797
(800) 553-3332
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