Naim has lengthy embraced two improve paths: the standard substitution routeexchange an inferior part with a more recent or higher oneand progressive power-unit augmentation for parts already put in. Setting apart for now the previous route: Amongst many different modifications, these Naim “New Traditional”sequence parts could also be extra simply mixed not solely with different parts from Naim however with gadgets from different audio makers. This enhanced compatibility contains Naim legacy methods: All can now be blended and matched extra simply.
Naim Audio’s enduring, compact 200-series stereo energy amplifier has been relaunched because the NAP 250, a key part of their new 200 Sequence. It has been up to date massively in its know-how and the compatibility of its connections, but the first circuit idea, which dates to the mid-Nineteen Seventies, is basically unchanged. Current growth work has targeted on serving to the amplifier match up properly with the brand new NSC 222 streamer-preamp, the NAP 250’s supposed companion. The brand new 200-series energy amplifier is now referred to as, merely, NAP 250, dropping the “DR” of the earlier mannequin. However whereas the suffix is now omitted, the ultralow-noise DR know-how has been retained within the energetic, absolutely regulated energy provides; certainly, it has been improved.
For comparability, I needed to hand a really current pattern of the now-superseded NAP 250 DR.
If it isn’t broke, repair it anyway
Over time, I’ve examined a number of iterations of the 250. The outgoing “DR” model of the NAP 250 carried out properly in my current analysis in HiFiCritic (Vol.16 No.1). Nonetheless, to raised match the design and connectivity ideas envisaged for the brand new 200-series system, quite a few operational and system modifications had been utilized. That engineering course of was allowed to run and run, leading to a significant design overhaul, adequate to benefit a contemporary appraisal.
Externally, the standard, green-illuminated Naim emblem is now as an alternative illuminated white, which can show disconcerting for some diehard Naim followers. The brightness could also be adjusted to swimsuit ambient gentle depth on all of the models by way of a system management app or a back-panel button, however inexperienced can’t be restored. The previous, shallower, all-alloy profile has been changed by a brand new one with flanking sections of thicker alloy with a sophisticated, recessed heart part in black acrylic, to raised harmonize with the remainder of the 200 sequence.
Conventional aluminum-alloy building is maintained to keep away from the potential for ferromagnetic interplay of the energetic electronics with the casing. The previous, nonstandard connection to the only unbalanced dual-channel XLR enter has been supplanted by a pair of standard-format XLRs for the L and R channels. These at the moment are absolutely balanced, with larger enter impedance (47k ohms balanced, up from the unique 18k ohms) in order that they draw much less present from the sign supply. With the suitable cable termination, the NAP 250’s balanced inputs could also be pushed from unbalanced sources due to the common, self-balancing input-circuit topology. This connection, which Naim refers to as “legacy,” has a considerably decrease enter impedance, specified at 34k ohms, however that is nonetheless usefully larger than 18k ohms, the worth on the earlier “DR” model. Although output impedance is not specified, if the desired damping issue (36 with an 8 ohm load) is correct, it’s about 0.2 ohms (footnote 1).
The loudspeaker output connections are unchanged from earlier fashions: Naim-standard, spaced 4mm sockets, for which Naim additionally makes a reasonable, proprietary, dependable bipolar plug designed to make sure unambiguous polarity. Non-paired 4mm plugs can also be used. The NAP 250 incorporates eddy-current suppression on the loudspeaker output connections, in frequent with the reference-level Naim “Assertion” energy amplifier. In most amplifiers, these connections are made via a conductive-alloy again panel, which supplies rise to a circulating present within the chassis-plate area between the + and connectors. In Naim amplifiers, this minor concern is nulled by introducing a small horizontal “insulating” slot between the usual Naim connectors at the usual 19mm spacing.
Efficiency upgrades embrace elevated 8 ohmrated energy, now a full 100Wpc into 8 ohms with each channels pushed, rated very conservatively at 0.1% THD+N. Quite extra energy is obtainable for decrease impedance hundreds. The amplifier is now rated at 190Wpc (at 1% THD+N) into 4 ohms with each channels pushed. A 2 ohm “flat-out” toneburst score of 300Wpc (up from 250Wpc) is in keeping with the rise in peak present to a specified 28A. This enhance in headroom guarantees higher general linearity.
Repeatedly working past the rated energy will trigger a low-noise cooling fan to activate, after {that a} non permanent thermal shutdown. (Naim calls the amplifier “party-proof.”) Reset is computerized. The amplifier runs cool at modest energy, barely heat to the contact and higher for the setting.
Naim designer Steve Sells defined to me that in gentle of the prevalence of high-definition digital audio, the 250’s bandwidth specification has been prolonged; the frequency response is now specified at 1.4Hz100kHz, 3dB. The earlier NAP 250 DR was rated at a a lot narrower 20Hz20kHz but additionally with narrower limits: 0.5dB. The desired voltage achieve is now 29dB, or an element of about 30 occasions. The enter sensitivity stays fairly excessive at 1V for full-rated output, comparable with earlier Naim product ranges. This reasonably excessive sensitivitylarger than most amplifiers from American designersmakes the NAP 250 a greater match with direct-connected, volume-controlled DACs that output a nominal 2V full scale.
The brand new NAP 250 additionally enjoys an influence provide redesign. The chunky, 1kVA-rated toroidal core transformer is sustained, however regulation is improved, with decrease copper losses (thicker wire!). Revised thermal annealing after meeting is alleged to decrease inside stresses. Reservoir capacitors with the next working voltage are fitted; that is well-known to carry efficiency by serving to to scale back artefacts that may happen in these internally complicated, wound foil, passive parts; pure capacitance they don’t seem to be!
One factor that hasn’t modified is the long-established, quasi-complementary, all-NPN transistor output topology. Circuit enhancements embrace liberal use of discrete, multiple-transistor constant-current levels with improved supply-rail noise rejection. The whole circuit board has been relaid for extra logical sign paths. Superior, low-capacitance, thermally conductive aluminum-nitride heatsink insulators, beforehand used on the output transistors, at the moment are additionally fitted to the regulators. Their decrease capacitance ought to cut back stray coupling to the chassis. The time fixed chosen for output-stage biasing has been lowered to the infrasonic, aiding low-frequency part response. Full regulation of the availability rails has been retained.
As a result of the amplifier is now absolutely balanced, the enter stage includes two Naim enter achieve levels per channel. This format is claimed to ship “an sudden enchancment in sound high quality,” which Naim says is supplemented by the accompanying redesign of the low-level, DR-stabilized provide rails. (“DR” stands for “discrete regulator”; regulation just isn’t carried out by an IC chip.) These low-noise “DR” regulators are additionally deployed for the subsidiary energy provide rails and serve to scale back the noisefloor.
A retuning of the general suggestions/stability margin is claimed to contribute to raised sound high quality, augmented by larger output-current headroom, helpful for driving lower-impedance hundreds right down to a newly specified 2 ohms minimal impedance. Additionally price noting is the retention of the standard 60dB channel separation specification, fixed over the total audio bandwidth. Extra separation is technically potentialhowever would it not make the sound worse? Naim argues that it might (footnote 2).
When put in in an all-Naim systemallow us to say with its partnering NSC 222 streaming preamplifierthe amplifier powers up silently in 4 levels. This course of could also be synchronized optically with the opposite matching audio models, avoiding undesirable noise from earth leakage currents. By this and different means, stray electrical noise is rendered inaudible.
The NAP 250 sounds fairly good fairly quickly after powering up. A soft-start power-breaker module derived from the Assertion design helps cut back stress on the mains enter fuse. An auxiliary energy provide initiates startup then shuts down as soon as the amp is absolutely powered. Beneath regular use, the heatsink fins flanking the case will silently cool the amplifier, however whether it is pushed unduly exhausting or at excessive ambient temperatures, a low-noise, variable-speed cooling fan begins up. To fulfill world effectivity rules, standby is invoked if the NAP 250 is silent for greater than 20 minutes.
Absolutely regulated energy provides have a tendency to offer the subjective impression of considerably extra energy, for instance, with the bass sounding as if the ability transformer and reservoir are significantly bigger than those fitted. Incessantly there are efficiency features in different areas comparable to transparency and micro element, however when judged subjectively, provide regulation remains to be not a totally convincing substitute for extra energy, comparable to one with an enormous 34kVA transformer having sometimes 300,000µF of reservoir capacitance. The distinction turns into evident when driving bigger audio system able to prolonged low frequency at excessive energy, regularly with a taxing, low-impedance loading. With their ultra-heavy loading, such audio system can typically reveal the amplifier energy provide’s character within the ensuing sound high quality, though most amplifiers are designed to keep away from this unwelcome affiliation through the use of unfavorable suggestions to keep up a low output impedance and thus to raised meet the reactive present demand.
