-~ VALVE AMPLIFIER // ~.~.-~~~~~ Made by: NAT High End Amplification, Serbia ~y~!I.~ ~~~~~ Supplied by: Alternative Audio ~TILTI : ~

Telephone: 01984 624242 ~ ,% Web: www.alternativeaudio.co.uk, ] [, ~

NAT Sel J\1kII (£6762)No, this isn't Japanese exotica - it's a world-class, single-ended triode powerhousefrom Serbia! If you've had your fill of 3006s, then here's a real he-man's ampReview: Ken Kessler Lab: Paul Miller

Confession time: Serbia is not onmy list of 'Top Countries ThatProduce High-End Equipment'.Before the arrival of the NAT

Sel Mkll, I wouldn't have even used thewords 'Serbia' and 'high end' in the samesentence, unless it was, 'I doubt thatthere's much high-end kit in Serbia.'

Stupid, arrogant me: NAT'sSe1 Mkllmonoblock is nothing short of glorious, soit was my loss, not theirs.

But even before waxing lyrical aboutthe sound quality, the fit and finish, thefast warm-up, the delicious details, I haveto mention the single most importantaspect of the Se1 Mkll as far as my ownaudio prejudices are concerned. Because itfeatures a 211 triode, I was automaticallypredisposed toward it, much in the sameway that the presence of black olives add apoint to the score of any dish I might eat.But the Se1s arrived not with reproduction211 s: they came with 211 s packed in theiroriginal, circa-1945, military-issue boxes.NATswears by new-old stock (NOS)tubeswhenever possible.

A GLASS ACTWhy do I get stupid whenever I see a 211?Maybe I'm in a minority. but for me it's oneof only a cluster of valves - 845s also cometo mind - that realises, or even exceeds thefull bull hype ascribed to 300Bs but rarelyachieved. They are liquid, warm, involving,magical and able to deliver enough powerto drive something other than a frikkin'horn. And while I'm not going stake my lifeon NAT's 35W rating for a monoblock witha single 211, I have always found them tobe embarrassingly more robust, powerfuland palpable than any 300B.

As the images show, the direct-heated211 enjoys pride of place on the Se1Mkll. The suffix indicates that this versionimproves on its predecessor with a powerincrease thanks to a 'special driver, super

RIGHT: Theheart of the amp - a direct-heated211 triode tube from GeneralElectricand'packagedunder the direction of the ChicagoSignalDepot' on April 30th, 1945

tube', a military-grade 6N30P-DR; thethird valve in the Se1 is a 6N2P-EV.Thelayout is very much in the current fashion,with a long chassis but a narrow frontalaspect - not a problem for a monoblockwhich only has two controls on its 10mm-thick aluminium fascia: on/off and a rotaryto select impedance and zero or lowfeedback. Directly behind the tubes arethe output transformer and the powersupply. All that's left are the sockets onthe rear panel, including IECmains input,fuse sockets, paralleled XLRand RCAphonoinputs and WBT speaker terminals.

NATdesigned the Se1 with a shortsignal path free of passive components.In NATpractice, that describes a circuitwith no coupling capacitors, nor inter-stage transformers. Their transformersare hand-wound, proprietary designs, towhich NATattributes improved frequencybandwidth. Indeed, they boldly state thatthe frequency response is 9Hz-60kHz.

Operation is pure ClassA, with zerofeedback, but you can also dial in a smallamount of feedback from the front panel

rotary, for certain speakers or conditions, ifyou so desire. The bass tightens up with alow feedback setting, at the cost of sometransparency or air. It's purely a matter oftaste, as it's subtle rather than coarse.

Given the rarity of NOS 211 s, you wantto know that the tube in your amp is beingcosseted. NAThas fitted the Se1 with anautomatic bias circuit, so the user needsnot worry about adjustments. According toNAT,'sound quality is totally independentagainst power supply instability, because allstages in the amplifier have stabilisation.'

The impedance/feedback knobaddresses only 4 or 80hm speakers; I usedthe latter with 150hm LS3/5As.They do,however, recommend speakers of over90dB (at 80hms) sensitivity, which I foundpossible to ignore: the amps workedperfectly in my 12x 18ft room with SonusFaber Cremona Auditor Elipsa and WilsonSophia 2 as well as LS3/5As.Indeed, theypositively adored the latter.

Although hefty and chunky at 25kgapiece, and needing floor space of300x520mm - they're also relatively tall

28 I www_hifinews.co.uk I AUGUST2010

at 260mm - the Se1 Mklls were up andrunning in record time after completingthe brief 'soft start' procedure to preventthumps - and I mean record time. It wasas if they needed no warm-up time toreach their optimal performance. Thecompany states that every unit enjoys a1OO-hour burn-in at the factory, which alsoaccounted for the speed at which I felt theamps were ready for assessment.

YTERcables were used throughout.Marantz's CD12/DA 12 CD player fed theAudio Research Ref 5 preamplifier, thelatter driving the NATswith XLRcables eventhough the amps are not balanced: theXLRsare there in what the company calls'pseudo-balanced.'

@ READY, SET, GO ...Aaah, SETs!My greatest love-hate in all ofaudio, though horns come close. Anyonecan hear why 300B single-ended triodes

NAT'S TUBE FIRSTS

LEFT: The lone rotary helpsfine-tune the soundfor matching feedbackto a specificspeaker;minor benefits alsooccur from disc-to-disc

digging out some Cajun material to hearif my suspicions were correct: the NATSe1 Mklls are almost embarrassingly freeof extreme treble issues. Indeed, you'llwonder how they manage to removeso much of the sibilance from bright

recordings without robbing the music ofother high-frequency information.

seduce so many listeners: they're thecomfort food, the guilty pleasure ofhigh-end audio, like an occasional Big Mac.But haute cuisine they ain't, for they arefar too flawed to be taken seriously: powerissues, soft frequency extremes, bass sorelyin need of audio Viagra. On the upside,they caress vocals,they can on occasionimage like a David Leanproduction, they rarelyinduce listener fatigue(they merely put you tosleep) and they allowtheir owners to beinsufferably smug.

What the NATsencourage you to listento is not far removed from what appealsto SETusers in general. They love strings,never delivering a violin screech unlessthat's what the musician played. There'sa silkiness to the top end that had me

BLINDING BOLDNESSIs the treble rolled off? If so, itcertainly doesn't sound that way.With the pedal steel on the newPoco live album, recorded for asmall audience at CBSstudios backin 1971, the metallic chime thatdistinguishes that instrument fromall other string-driven-things rangthrough with blinding boldness andclarity. Utterly absent was any tubehaze, despite the 211 s in use beingmade around the same time the

Second World War was ending.Poco, too, possessed a percussionist in

George Grantham with imagination andpower. His apt use of woodblock camethrough with exactly the sound I rememberas a kid, standing mere yards away frommy brother as he practiced. It had the rightattack, the correct, authentic overtones.

Anyone who attributeslifelike sound to SETs,especially if a short,uncluttered signal pathis part of the recipe,will glow just like the211 doing all the hardwork. This amp sings inthe truest sense.

Not only my preference, but also oneof SETs'greatest virtues, is the femalevoice. I rarely listen to Rickie Lee Jonesbecause her music makes my skin crawl,but I have to admit her voice is interesting,a mix of textures as far removed fromLinda Ronstadt as one could get, whilenot emulating the soul diva raunchabilityavailable from Aretha to Alicia to Dustyto Bonnie. Feeling masochistic, I dug out'Easy Money', that most egregious ofaudiophile cliches, only to discover that theNATrendered it involving on a number ofunexpected levels.

It juggled richness and detail in equalmeasure, the iconoclastic percussivetouches (tambourine?) enjoying the samein-the-room clarity and chiming as Poco'spedal steel. Her voice slithered - maybe it'sher reptilian vocals that suggest she couldbe a cast member of V - with the flow G>

'Thosewhoattribute lifelike

sound to SETsl willglow like the 2111

However crass this sounds, the NAT is a shocker because it comes from Serbia_With all due respect to any Serbs reading this, it's not like the country has animpressive track-record for high-end valve amps_ Which makes the Sel Mklldeceptive: its fit and finish are the antithesis of the other newbies, the still-learning Chinese. If anything, the workmanship approaches that of the Japanese.

NAT's focus is on valve pre- and power amps, the company preferring triodes,short signal paths, zero or low feedback, NOS tubes and the single-endedtopology. And it's not slavish copiers of existing circuits. It claims a numberof tube firsts, including a direct-coupled, zero-feedback line-stage; a battery-powered, zero-feedback phono stage; a 160W, direct-heated triode, anode-coupled, zero-feedback, single-ended power amp, etc. I stand corrected_

AUGUST2010 I www.hifinews.co.uk I 29

~ VALVE AMPLIFIER

LABREPORT

ABOVE: Both RCAand XlR inputs are single-ended while the single 4mm speakeroutput posts are coupled to both 80hm and 40hm transformer taps via a front switch

dense tracks delineated so that youcould ascribe front-to back depthto what you know were recordingsbuilt up in the studio. And that basson 'I Want You (She's So Heavy)' - itslithered across the floor like the fogin a grindhouse horror flick: palpableyet elusive, enveloping yet opaque.

But then you experience thisamplifier's majesty: 'She Came InThrough The Bathroom Window'taunts any system to rise to theoccasion. Power, grandeur, clarity,all in a musical fragment. The NATdelivers it to the listener on a plate.Meissen, set in front of you by awhite-gloved waiter. (I)

that also renders bass either fluid(good) or static (bad). This is onelush, liquid-sounding amplifier,without giving the impression thatit's also lacking control.

GET THE FUNK OUTAs a rule, I try not to waste mytime nor yours when reviewingSETs by feeding them funk. Frommy experience 300B-equippedSETs.are categorically the leastcapable amplifiers I can imagine foraddressing classic era Temptations,early Hall & Oates, any Sam &Dave. There's no better track forembarrassing 2W amplifiers thanMel & Tim's 'Too Much Wheeling AndDealing', which has rolling Stax bass,sassy southern horns and duellingvocals. Oh, the punch! The attack!Damn, is this amp fast and tight andcontrolled. And yet, there's neverany transistor-like over-etching, noglassiness, no harshness. They climbwithout unnecessary drama, stopwhen the note ends, or fade withthe requisite decay. They make evenold CDs aurally palatable.

It almost goes without sayingthat the spatial concerns aredispatched almost with insouciance.Using the Toshiba-EMI 1983 CDof the Beatles' Abbey Road, theimaging was to-the-millimetre

the layering of the more

For me, a no-brainer: the 211 haslong been my fave tube: it's oneof the few that, when used as asingle-ended triode, possessesreal guts. It is the 300B's sexy,classy, funky evil twin, AngelinaJolie instead of Barbara Cartland.But the best surprise - and thissounds terrible if you're politicallycorrect - is that such a staggeringamplifier comes from a countrywith no tradition for high-endgear. I love it.

Sound Quality: 88%o

NAT Sel MIdI (£6762)Sixty-five years since this direct-heated 211 triode left theGeneral Electric depot it is realising a new and surprisinglyimpressive lease of life in this (genuinely Class A) single-endedpower amp from NAT.Tested in 'low feedback' in preference to'zero feedback' mode, the Se1 Mkll fully stabilises within justone minute of switch-on. There's no protracted warm-up periodas the Se1 Mkll achieves 0.096% distortion at 1kHz/5W/80hmin under 60 seconds, a figure maintained to within 0.001% overthe subsequent two hour lab test period.

Power output is not the 35W claimed by NAT (with noreference to frequency, load or distortion I might add) butrather closer to 23W/80hm at 1%THD and 27W/80hm at 2%THD. Via the 40hm tap it achieves 18W/40hm at 2% THD whileunder dynamic conditions it's possible to realise 27W, 22W (3%THD), 12.5W (4% THD) and 7W (5% THD) into 8, 4, 2 and 10hmloads [see Graph 1, below]. Sensitive, easy-to-drive speakersare a must even if the very linear 1.3ohm output impedance isquite low by valve standards. The A-wtd SIN ratio of 87.9dB (re.OdBW) is respectable just as the response is sufficiently flat andextended (-0.2dB at 20Hz to -0.8dB at 20kHZ). The latter willvary somewhat with speaker load impedance, however.

Distortion increases gently with output (0.056% at 1W to0.55% at 20W) and at very low bass frequencies (1. 7%/20Hz to65%/5Hz at 5W/80hm) while the limited feedback also pushes itup at the top end (4.5%/20kHz - see Graph 2, below). Readersare invited to view a comprehensive QC Suite test report for theNAT Se1 Mkll mono block power amps by navigating to www.hifinews.co.uk and clicking on the red 'download' button. PM

00 1~~ ~~

100Dymtni.t ft~1'i OutfH""" ~

ABOVE: Dynamic power output versus distortion into80hm (black trace), 40hm (red), 20hm (blue) andlohm (green) speaker loads.

ABOVE: Distortion vs. frequency from 5Hz to40kHz (5W/8ohm)_ Distortion still increases at thefrequency extremes in 'low feedback' mode

HI·FI NEWS SPECIFICATIONSn_"._H"L .. d_'_~"~ nO. ,. 1 __ "., on ...

1'173771Power output «2% THO. 8/40hm) 27W /18W

Oynamic power «5%TtiO, 8/4/2/10hm) 27W / 22W /12.5W /7W

Output impedance (20HZ-20kHz) 1.30-1.010hm

Frequency response (20Hz-100kHZ) -0.2dB to -14.2dB

Input sensitivity (for OdBW/20W) 253mV /1130mV

A·wtd SIN ratio (re. OdBW/20W) B7.9dB/l00.9dB

Distortion (20HZ-20kHz reo 5W) 0.087-4.5%- -

Power consumption (Idle/Rated o/p) 195W/195W(each)

Dimensions (WHO) 150x260x520mm (each)preCise,

30 I www.hifinews.co.uk I AUGUST 2010

- 100