Counterpoint Natural Progression NPS-400 power amplifier

This review was first published in March 1995

Amplifier designers have frequently looked for ways to marry the advantages of tubes to those of solid-state devices. Hybrid designs of various stripes have appeared over the years, most of them using tube input stages with transistor output stages, eliminating the major weaknesses of tube amplifiers: eg, they run hot, are unreliable in that tubes have a finite life, are more expensive than a similarly powerful solid-state design, and have power-hungry output tubes and output transformers.

Counterpoint Electronics has long been a leading proponent of this design approach. In 1992, they introduced their new Natural Progression Mono power amplifiers, building on the hybrid design topologies they had long been using in their earlier amplifier designs. Some of this technology has now filtered down into a pair of less-expensive, Natural Progression stereo power amplifiers: the NPS-200A and the NPS-400A.

The imposing NPS-400A ($4395) is large, heavy (65lb), and clearly well-built. The front panel has a single two-position power switch and a single LED indicator. This LED indicates either standby (red) or operate (green), and blinks on and off during the transition from one to the other. In standby, the B+ (high-voltage) supply to the tube heaters is turned off. The tube heaters, however, are left on to reduce thermal cycling. The output stage remains on in standby.

On the rear panel are balanced and unbalanced inputs for both channels (each with a balanced/unbalanced selector switch), along with input muting switches (useful for swapping input cables without having to turn the amplifier off). There's also a switch that selects bridged operation, and two pairs of five-way binding-post outputs per channel (for bi-wiring, if desired). The good-quality binding posts are of the finger-tighten variety—I strongly prefer hex-head posts, which are usable with a nut driver (for audiophiles who can't resist the urge to tighten them beyond reason). There are output protection fuses for each channel (along with internal power-supply rail fuses), and a power-line fuse in the connector for the detachable power cord.

Internally, a massive, 2kVA power transformer is located front and center, with eight large power-supply filter caps. There are two vacuum tubes (a 6DJ8 triode for amplification and a 6CA4 rectifier which is used for the high-voltage supply to the 6DJ8) per channel, along with eight solid-state output devices.

The NPS-400 Natural Progression design uses a high current gain, high input impedance, bipolar transistor output stage—not the IGBTs, or Insulated Gate Bipolar Transistors, of the Natural Progression Monos. The vacuum-tube input stage, however, does use the same configuration as in the Monos—to quote Counterpoint, "a dual triode configured as a differential common-cathode amplifier, with bipolar constant-current cathode and anode loads." If this doesn't ring any bells with you, don't worry. The net objective is to lower the distortion of the input stage, which is said to be low enough that no loop feedback is required. The NPS-400 does not, in fact, use feedback at all in its amplification stages [other than the output stage's usual cathode-follower feedback—Ed.].

A feedback loop is used for the DC servo, however, to control DC offset. This loop includes only the output stage, where Counterpoint argues that the only significant DC offset errors occur.

My thoughts about the NPS-400A remain ambiguous—even after listening to it for a considerable amount of time. It's only fair to state this up front. While I normally try to use a maximum of two loudspeakers (one primary and an alternate, if necessary) in evaluating a power amplifier, with the Counterpoint I used three. I also freely substituted among the cables noted in the "System" section.

The NPS-400A presented a large, expansive soundstage. The chorus on Laudate (Proprius PRCD 9100) had bloom to spare, with open textures and a convincing sense of space. The amplifier's sound had life and detail, with a reasonably neutral, if just slightly forward, perspective. The Counterpoint was also capable of superb performance on simply scored material. Vocals over the Dunlavy SC-IVs and the Energy Veritas 2.8s, in particular, had an in-the-room quality. Soundstage precision, particularly on the Dunlavys, was superb laterally, with a good, though not exceptional, sense of depth.

Neither did the Counterpoint lack for power. While its bass quality varied from loudspeaker to loudspeaker, at its best—with the Energys—its extension and weight were exceptional. It definitely energized a room on material having a strong bottom end. The Counterpoint's bass impact, while often unnervingly good, was surprisingly less evident on the Dunlavys. In fact, the operative word for the bass through the Dunlavys was "tight"—even a little lean (the Dunlavys do sound tighter and leaner in my large listening room than they do in Robert Deutsch's smaller one). The same was true of the midbass, which was fuller and richer, but less defined, on the Energys than on the Dunlavys.

Through it all, however, I was bothered by a slightly dry top end—it was almost grainy, though that term may make too much of the problem. This dryness wasn't always in evidence—frequently I was able to just go with the flow. While the Counterpoint was clearly doing more right than wrong, the dryness did bother me often enough that I couldn't ignore it; once I began comparing the NPS-400A with other amplifiers, this dryness became an itch that I couldn't quite scratch.

On the Mirage M-7sis, hard percussion sounded very slightly splashy with the Counterpoint—not a true brightness (which lies in the low to mid treble), but rather an aberration that seemed a bit higher in frequency. Climaxes, such as those on Laudate, turned a bit silvery. The top end of the Krell KSA-300S was noticeably cleaner and more liquid, with less strain on peaks and a more natural reproduction of ambience. The more expensive Krell unquestionably won out in this comparison.

Counterpoint Electronic Systems
Company no longer in existence (2021)

Glotz's picture

More hybrid AB amps need to come out!

Or impress us with more tube hybrid Class D... Rogue and AVA come to mind along with AR.

And thank you for the PS Audio '1200 review.