Naim Audio is a specialist British manufacturer of high-end audio amplifiers well known for their self described qualities of "pace, rhythm and timing". The company has a sui generis approach to audio design, ignoring specifications and power ratings as indicators of the quality of an amplifier. Naim's approach includes, but is not limited to, absence of tone controls, the use of the DIN connectors instead of the RCA connector used almost everywhere in the home audio equipment industry, and reliance on over-engineered external power supply units (PSU) to deliver current for musical transients. The company's two-channel NAP 250 amplifier made its début in 1975.
History The company, established in 1973, is one of the best-known hi-fi manufacturers in the UK. Its first product was a power amplifier named NAP 160; this was soon followed by the NAC 12 pre-amplifier. Until 1985, Naim's activity was centred on audio amplifiers. The two-channel NAP 250 power amplifier that made its début in 1975 is among Naim Audio's most well-known analogue products. Its basic circuit layout would be the model for its power amplifier range for more than 25 years, until the introduction of the flagship NAP 500 in 2000.
Philosophy All of the early models were designed by Naim founder Julian Vereker, who wanted equipment that he himself and friends could enjoy listening through. He experimented with constituents of the sound reproduction chain: source components, amplifiers and loudspeakers. Received wisdom was that amplifiers were "straight wires with gain" that had no effect on the sound, but Vereker insisted that the performance of amplifiers on the market ranged from bad to abysmal. Vereker took some 12 months to learn enough about electronics to design the first product initially for personal use, named the NAP 160. Vereker defined that the amplifier's premise was "to drive the loudspeaker with a musical signal such that I could compare the sound with live music and get the same degree of enjoyment", and then determined that the amplifier must be able to drive loudspeakers' "widely varying impedance under musical conditions" without information loss.
Design principles
Audio circuitry Vereker believed that loss of information, often due to overload protection, was a damaging type of distortion that amplifiers were vulnerable to. Vereker attempted to reduce information loss at the design stage, by unconventionally disregarding test-bench measurements of harmonic distortion performance and output into a static resistive load. Naim says that to achieve amplifiers with low harmonic distortion, low noise, wide power-bandwidth, and constant dynamic output impedance, they pay attention to balancing dynamic impedance, open-loop bandwidth, slew rate, and propagation delay; the amplifiers are not subject to slew-rate limitation between 5 Hz and 50 kHz. Vereker believed that a properly designed amplifier would not need tone controls, since these filters were often palliatives for poor design. He contended that tone controls represented a cost of manufacture yet were detrimental to sound quality. Therefore, starting with the NAC 12, Naim amplifiers have never featured the tone controls that were popular elsewhere in the industry. Vereker considered Naim amplifiers belong to the "class B" category where bias current is minimised. He believed that "class A" design was wasteful and masked significant design issues. Electrically, the pre-amplifiers are bandwidth-limited, and while Naim is open to the possibility that users might match their pre-amps with another make of power amplifier, Naim warns against using other makes of pre-amplifiers with Naim power amplifiers, arguing that the former define the operating parameters of the latter and guarantee its stability. In practice, modern products' bandwidth has been much extended, but the pre- and power-amplifiers are of such a tight operational fit and sonic synergy that they are rarely used with other makes.
Power source Naim has from the outset externalised pre-amplifiers' power source, unlike other manufacturers, citing the undesirability of having AC and transformers' powerful magnetic field near sensitive pre-amplifier circuitry – the "key point of separates". Its over-engineered power supplies, aimed at ensuring adequate 'headroom' (ample reserves of power) for transients, are equally well-known. Naim strongly believes that an ample source of power is of the greatest importance, and the availability of external PSUs to accompany its products also reflects the philosophy. The performance of most of its pre-amplifier range benefits from adding one of a number of power supplies, which provide permutations for upgrading.
Output protection Vereker also believed that a well-designed amplifier must be stable at all times when driving real-life loads, which are different from those achieved in lab conditions because loudspeakers' impedances vary with frequency. The inherent compromise between the pursuits for stability and sound quality means that Naim's power amplifiers are designed to work optimally with its own moderately priced NAC A5 speaker cable, and its predecessor NAC A4. Product manuals warn users against using "high-definition wire or any other special cable between amplifier and loudspeaker". Whilst other manufacturers habitually employ Zobel networks (or an output filter which enhances amplifiers' stability) to protect against use with speakers and or cables with very high-capacitance, Naim amplifiers routinely omit these filters because of their adverse effect on sound quality. The design decision was made to use a suitable length of speaker cable (a minimum of 3.5m, with 5m being optimal) to provide the effective inductance.
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