Solid State Power Amp Reviews

Back in 1970, one Julian Vereker decided to record some musician friends in his house in Salisbury, England. Using standard, off-the-shelf electronics and tape machines, he was startled at how dissimilar the recording was to the sound of live instruments. As a result, he started designing his own recording electronics, including a recording console, of which he sold several to local broadcast facilities.

Spurred by this success, Julian founded Naim Audio to design and manufacture home playback equipment that more closely approached the sound of real music. Naim has since become one of the largest hi-fi electronics manufacturers in the UK, employing about 60 people. The brand is highly regarded in England and is exported to 30 countries, including those in the Far East. Interestingly, the preamplifier and power amplifier topologies have remained virtually unchanged since the very first Naim products. It is significant that Naim's 20-year success is based on the same circuit.

Naim products are also unusual in the way they are constructed. Rather than making the products in assembly-line fashion, each worker builds a component from the chassis up and sees it through to final test. By inserting the pre-stuffed printed circuit boards, jacks, transformer, wiring, and mechanical components, the builder has a greater identity with the product than if he/she installed just one part repeatedly in many units. In addition, each product is individually listened to before it leaves the factory, assuring reliability and consistency. Listening to each unit as part of the manufacturing process reflects Naim Audio's fundamental belief in the importance of the listening experience: Naim provides very few or no specifications on their products, preferring that potential customers decide by listening. Incidentally, Naim has an outspoken disdain for digital playback.

During the 20 years since Naim Audio's founding, the company has pursued an individualistic, idiosyncratic course that has set it apart from other hi-fi manufacturers. Instead of building components designed to work well with a wide range of products from other manufacturers, Naim has maintained the philosophy that the best music playback system is one in which all components have been optimized to work with each other. In addition, Naim believes that making equipment conform to existing standards inevitably involves compromising the system's musical performance. This philosophy is reflected in the nonstandard DIN jacks found on all Naim equipment, BNC phono inputs, and unusual preamplifier power-supply arrangement. Taking this idea even further, the loudspeaker cables are considered part of the amplifier design, suggesting that cables other than Naim's should be avoided. Even installation in the customer's home is considered in the overall system design: Naim dealers set up the system for the customer and will even demonstrate the equipment in the potential purchaser's home.

In fact, Naim's five-year warranty specifically states that use of cables and interconnects not supplied or recommended by Naim, or use of "unsuitable" combinations of Naim and non-Naim equipment, constitutes "abuse" under the warranty terms.

This approach, which places system integration and performance over individual component versatility (or to put it more bluntly: "We're doing what we think is right, the rest of the world be damned"), has resulted in products very different from those I am accustomed to. When I unpacked the three Naim units for this review, I felt a combination of apprehension and anticipation, based on my only other experience with a Naim product, the $875 NAIT 2 reviewed in Vol.12 No.9. I remembered my hassles with the NAIT 2's nonstandard jacks, but also its extraordinary musicality and ability to involve the listener in the musical performance (ST also raved over the NAIT 2). I thus approached the review of these three products with ambivalent feelings.

When evaluating a component, I feel it is mandatory to leave all other variables in the system constant (music, associated components, cables, loudspeaker and listener position, etc.) to isolate the character of the unit under audition. This was clearly not possible with the NAC 62 preamp and Hi-Cap power supply, nor with the NAP 140 power amp. Besides not being able to audition the units separately, the 62's DIN input jacks required that I use a Chord Company interconnect with RCAs on one end and a DIN plug on the other, as well as Naim's interconnect between preamp and power amp. Rather than chop up a pair of AudioQuest interconnects to install BNC terminations, I used a pair of BNC-to-RCA adaptors before being sent a Naim phono cable with integral BNCs. Finally, I discovered that 10' runs of bi-wired AudioQuest Green caused the 140 power amplifier to oscillate, necessitating my use of single-wired Naim speaker cable (more on this later). Clearly, these weren't components amenable to my usual review methods.

After a visit from Chris West, Naim's North American Technical Representative, who explained their overall system approach to music playback, I began to see the products in a different light. Rather than buck their system, I decided to approach the three units (along with their interconnects and loudspeaker cable) as an integrated system. Indeed, the NAC 62 and NAP 140 should be considered an integrated amplifier in two boxes (three with Hi-Cap), such is their compatibility with each other and incompatibility with other components: Naim specifically recommends against using the 140 with any preamp other than a Naim.

This experience caused me to reflect on the differences between Naim's approach and everyone else's. There is a certain type of customer for whom a Naim system is ideal: one who doesn't want to make decisions about which interconnects or speaker cable to buy, and isn't going to trade in his preamp with each new "Mark" designation. In other words, a Naim system is designed to be set up and forgotten, with the listener enjoying music through it rather than the music system and its continual tweaking and experimentation becoming a hobby. My reluctance to accept their methods reflects the fact that I constantly listen to different equipment and cables in a variety of juxtapositions as part of my job, a situation not predisposed to the Naim philosophy. Nevertheless, I decided to put away my prejudices along with my favorite interconnects/speaker cables and listen to some music.

I'm glad I did; I discovered a very special music playback system.

Naim NAC 62 preamplifier: $895
The NAC 62 is the lowest-priced and simplest of the company's three preamplifiers. Like most of the Naim line, the 62 is housed in a long, narrow, extruded aluminum case. The front panel reflects the 62's minimalist design, with just two large knobs (volume and input selection) and two small knobs (balance and mute/tape monitor). The front-panel lettering is difficult to read but inconsequential because of the unit's simplicity. The rear panel has five DIN connectors, three of them for signal input (marked "Tuner," "Aux," and "Tape," footnote 1) and two for connection to either a Naim power amplifier or external power supply (only one of which is used at a time). Phono inputs are BNC jacks rather than RCAs. With each preamp, Naim provides BNC terminations for fitting on an existing interconnect. Alternately, the user can buy from Naim a ready-made BNC phono interconnect with a variety of tonearm terminations. In systems without a phono source, the BNC inputs can function as an additional line input, with the line-input sensitivity adjusted by the dealer.

Rather than include the power supply within the preamp chassis, two of the three Naim preamps (the 62 and 72) get their DC from either a supply within selected Naim power amplifiers (the NAP 90 or NAP 140) or from an external supply like the Hi-Cap (the top-of-the-line NAC 52 preamp has a dedicated external supply). Keeping the power transformer away from low-level audio circuitry reportedly improves audio performance. If the NAC 62 is used with an NAP 90 or 140 power amplifier alone, 24V DC is carried to the 62 through a five-pin cable. The NAC 62's audio output travels in other conductors within the same cable harness.

The preamp supply within the NAP 140 comprises a bridge rectifier, a 3300µF electrolytic capacitor, and a TO-220 (three-pin) regulator. Naim places great importance on the power supply, especially in low-level circuits toward the front of the electronics chain. For this reason, they offer the Hi-Cap (for High Capacity) power supply as a replacement for the supply built into the two power amplifiers. The Hi-Cap is described below.

The NAC 62's circuitry is quite basic and contained on a single-sided pcb, except for the phono stage. In addition to being completely discrete, very few components are in the signal path. Two tantalum capacitors provide input and output coupling (the only caps in the line stage), while resistors are all 1% metal-film types. Five electrolytic power-supply decoupling caps are located next to each audio circuit stage. An expensive-looking Alps potentiometer provides volume control.

The phono section is located on two small vertical boards mounted toward the unit's rear. The phono circuit is somewhat unusual in that it provides some gain before RIAA equalization. Like all Naim circuits, the phono boards are discrete and employ 1% metal-film resistors and tantalum caps.

The boards are easily changed to accommodate different phono cartridges. The "N" version has an input sensitivity of 2mV and input impedance of 47k ohms for moving-magnet cartridges, the "S" version is 100µV/470 ohms for moving-coils, and the "K" version, at 100µV sensitivity and 560 ohm input impedance, has been optimized for the Linn Karma and Troika cartridges. For systems without a phono source, the phono boards can be replaced with "V" boards that provide an additional line input whose input sensitivity is variable (hence the "V" designation), allowing perfect level matching with a CD player or digital processor. A sticker on the preamp's rear panel identifies which phono option is installed. In addition, a stick-on letter designation on the board also indicates the circuit version. Changing phono boards is very fast and easy due to the gold-plated pin and socket arrangement. I had both the "S" and "K" versions available for the auditioning.

The 62's overall construction is excellent, with the layout refined by years of manufacturing the same product. The point-to-point wiring between pcb and input/output jacks is meticulous. Without a power transformer and DC supply, the NAC 62 is quite lightweight at just 8 lbs.

Naim NAP 140 power amplifier: $1295
The power output of Naim amplifiers is reflected by the model number, which represents the total power output into four ohms. The NAP 140 power amplifier, rated at 45Wpc into 8 ohms (70Wpc into 4 ohms), is housed in the same size and type chassis as the NAC 62 preamp and the Hi-Cap power supply, maintaining a uniform appearance between these different-functioning components. The front panel contains a large power on/off rotary switch the same size and location as the 62's input selector (and also the Hi-Cap's power switch), further adding to the three components' similar appearance. The rear panel has an IEC power-cord socket, a 4-pin DIN plug (audio input signal and DC output), and two pairs of banana jacks for loudspeaker connection.

Inside, the NAP 140's family resemblance to other Naim products is apparent. The amplifier's power supply and the 24V preamp supply are located at the unit's rear. The NAP 140's supply includes a moderate-sized toroidal transformer and four 4700µF filter caps, the caps mounted on a triangular-shaped pcb. No voltage regulation is used. A large ground area on the pcb accommodates one leg of each filter cap as well as ground wires from various points within the amplifier. This single-point grounding arrangement has been refined over the years and is said to be sonically important. As mentioned previously, a 3300µF cap and three-pin voltage regulator within the NAP 140 provide 24V DC to an attached Naim preamp.

The 140 is a dual-mono design (following the transformer), with each channel's circuit mounted on its own rectangular pcb about half the unit's width and a third its length. The front end is discrete, with a minimum of components in the signal path. Critical capacitors are tantalum and all resistors are 1% metal-film types. The output stage is unusual in that both transistors in each channel's output pair are NPN types. Typically, a complementary pair consists of one PNP and one NPN transistor. The NAP 140's quasi-complementary pair is said to improve sound quality by using identical transistors (which are custom-made for Naim). Each channel's output pair is bolted to an aluminum heatsink, which in turn is attached to the chassis. In essence, the entire chassis draws heat away from the output transistors. An output-stage temperature sensor shuts down the amplifier if it becomes too hot.

The NAP 140's circuit topology has remained virtually unchanged since it was first designed 20 years ago. However, the newer products sound better than their 20-year-old counterparts due to refinements in components and pcb layouts. Other improvements include the inclusion of custom output transistors and new grounding techniques. Overall voltage gain is 29dB.

Like the NAC 62 preamp, construction quality is first-rate. The amplifier has a neatness and well-thought-out look to it, especially the wiring harness.

Nai, Hi-Cap power supply: $1195
The Hi-Cap power supply is available as an upgrade to owners of a Naim 62 or 72 preamp and 90 or 140 power amp, or as an essential part of a Naim preamp when using another amplifier brand. Additionally, the Hi-Cap is required when using the 135 or 250 power amplifiers, which don't incorporate a preamp supply.

The Hi-Cap looks identical to the NAP 140 from the front, with just a round power on/off switch on the front panel. The rear panel houses four DIN jacks, capable of supplying DC to a Naim preamp or Naim electronic crossover. Only one unit can be powered at a time from the Hi-Cap.

The Hi-Cap is a dual 24V supply composed of a large toroidal transformer with two secondary windings that feed two full-wave bridge rectifiers. In each of the Hi-Cap's two supplies, filtering is provided by a single 15,000µF electrolytic capacitor, while voltage regulation is performed by a large (TO-3) regulator. Each regulator is tested for noise, with more rigid criteria than can be provided by the manufacturer. Like the NAP 140's output transistors, the Hi-Cap's heat-producing regulators are mounted on a heatsink attached to the chassis.

One would intuitively think this dual supply would power the preamp's left and right audio channels. Naim believes, however, that better sonics are obtained by separating the high-level and low-level supplies. One of the Hi-Cap's +24V outputs supplies the preamp's phono and low-level stage, while the other powers the preamp output-driver section. The 62's volume control is between the two circuit sections. The Hi-Cap's DC supplies are said to have less than 50µV of noise.

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Footnote 1: I interpret the label "Aux" instead of "CD" as reflecting Naim's scorn for digital playback