In the wake of the ambitious NAC S1 and NAP S1 Statement project, Naim Audio has recently revised its ‘classic’ amplifier line up to incorporate some of the more significant advances resulting from the exhaustive research and development for that flagship product.
In the second half of 2015, the NAP200, 250 and 300 all acquired the DR suffix; the NAP500DR has taken a little longer due to the more complex nature of its circuitry. To coincide with it’s release the company hosted an event to present some of the technical background behind the new amps and have the opportunity to compare new against old through the range.
Recently appointed CEO Trevor Wilson opened the day with brief introduction outlining Naim’s current status, with updates on Spotify and Tidal compatibility in hand for streamers, and confirming a continuing commitment to the traditional hi-fi separates market in which they are doing particularly well. It was then over to Steve Sells, chief designer behind the Statement electronics and subsequent DR engineering to explain some of the electronic theory behind the upgrades, supported by imaginative demonstrations to show its effectiveness in practice. This was followed by listening tests to compare the original NAP250, 300 and 500 against their updated DR counterparts driving Focal Scala V2 Utopia loudspeakers.
Introduced in 2012, the initial DR designated upgrade consists of replacing the long-standing LM317 integrated circuit used to provide power for low-level circuitry such as preamps and active crossovers with a new board of made up of discrete components. As such, it is applicable to the standalone power supplies and smaller power amps that incorporated circuitry to similar effect. The improvement has been well documented, and firmly substantiates the company’s long held belief in the importance of power supplies in the system.
DR - short for discrete regulation - is something of a misnomer when applied to the new power amplifiers. The regulation involved here is capable of delivering tens of amps when necessary, and always been made up of discrete components, with not a single integrated circuit in sight. However, research carried out for the requirements of the massive Statement amplifier led to a redesign of this circuit, resulting in far lower noise floor and superior current delivery. The regulation circuit now utilises a complementary pair of power transistors to supply current to the amplifier section, where the older topology used NPN-type devices for both the +VE and –VE rails. The actual output stage retains the quasi-complementary configuration, where identical NPN-type devices are used, and remains unchanged.
Rather like using a stethoscope, a demonstration allowed us to hear ‘inside’ a 250 amplifier and monitor the noise on the power supply while music was playing. The effectiveness of a regulated supply in cleaning up this crucial part of the circuit was immediately obvious, but more impressive was just how much better the new DR regulator was than the original circuit, audibly substantiating the claim that it is thirty times quieter.
The other highly significant factor in the DR makeover is the use of the NA009 power transistors, commissioned for the exacting demands of the Statement. This is a direct off-shoot of Naim’s close collaboration with semiconductor manufacturer Semilab over many years, and has enabled Naim to control design and fabrication to an unparalleled degree.
These unique devices are numbered and parameterised during manufacture, a process that allows precise matching from adjacent positions in the die from which they are fabricated. The benefits of close matching transistors are not only measurable in terms of lower distortion, but have a significant impact on performance, and that is borne out by controlled listening tests. Close examination of other factors – such as mechanical and magnetic properties – have resulted in the total elimination of ferrous materials in the construction of these transistors, while thermal considerations led to the development of aluminium oxide ceramics to couple the transistors to the heatsink. This is claimed to deliver more efficient thermal transfer and reduced bias modulation, while at the same time lowering the stray capacitance between the device and the metalwork, again minimising noise at a crucial part of the circuit.