NA­GRA CLAS­SIC PREAMP & CLAS­SIC AMP

CLAS­SIC PREAMP/CLAS­SIC AMP

Australian HIFI - - CONTENTS -

If your tastes lean to the un­usual and the ex­otic, and you like your hi-fi to be hand-made in Switzer­land, look no fur­ther.

If your tastes lean to the un­usual and the ex­otic, and you’re in the mar­ket for a pre-power combo, you need to in­ves­ti­gate Na­gra’s ‘Clas­sic’ Se­ries… in par­tic­u­lar its Clas­sic Preamp and Clas­sic Power am­pli­fier. They’re a world away from look­ing mass-pro­duced, be­cause they’re not. They’re hand-built in Switzer­land to ex­act­ing stan­dards—which you might have guessed sim­ply by look­ing at the pho­to­graphs above of them—and they com­bine the magic of valve sound with the might of solid-state.

NA­GRA CLAS­SIC PREAMP

Na­gra’s ‘Clas­sic Preamp’ is a hy­brid valve/ solid-state de­sign that uses a pair of 12AX7 dual tri­odes and a 12AT7 high-fre­quency twin tri­ode. Th­ese are minia­ture valves with a very long ser­vice life, so will rarely need re­place­ment. And, when it does come time to re­place them, you’ll have no dif­fi­culty ob­tain­ing them be­cause they’re ex­tremely pop­u­lar and quite com­mon valve types… un­like the valves used by some UK man­u­fac­tur­ers, for ex­am­ple, which are avail­able only from the man­u­fac­turer!

The strange-look­ing me­ter at the left side of the Clas­sic Preamp is what Na­gra calls a ‘mod­u­lome­ter’. It’s ba­si­cally an old-fash­ioned mov­ing-ar­ma­ture volt­age me­ter but Na­gra has rather clev­erly turned it ‘back to front’ so what looks like a knob at the front of the me­ter ac­tu­ally houses the op­er­at­ing parts, en­abling ac­cess for cal­i­bra­tion or re­pair with­out hav­ing to dis­as­sem­ble the chas­sis. Not that this is likely, how­ever… mov­ing-ar­ma­ture volt­meters are so re­li­able and ro­bust that one built 30 years ago will likely out­last an LCD or LED dis­play that was built yes­ter­day. Na­gra uses its mod­u­lome­ters for dif­fer­ent pur­poses on its var­i­ous prod­ucts.

The one fit­ted to the Clas­sic Preamp shows volt­age at the pre-am­pli­fier’s out­put ter­mi­nals (though in deci­bels ref­er­enced to a 1 volt out­put, rather than di­rectly as volts).

The tog­gle switch to the left of the mod­u­lome­ter is not a power switch, as you might have guessed, but a spring-loaded multi-select ac­tu­a­tor which al­lows you to ad­just the bright­ness of the mod­u­lome­ter’s back­light­ing through six lev­els as well as turn it off.

Just to the right of the mod­u­lome­ter is a LED dis­play that shows the in­put source you’ve se­lected by ro­tat­ing the elec­tron­i­cally-ac­tu­ated rotary con­trol to the right of the dis­play. In its de­fault mode it cy­cles through the five avail­able in­puts show­ing in turn XLR, RCA-1, RCA-2, RCA-3 and RCA-4, with re­lays click­ing with each se­lec­tion. As you can see, all in­puts are line-level types—there is no phono in­put, so if you want to con­nect a turntable, you’ll need an ex­ter­nal phono pream­pli­fier.

De­spite the source switch­ing be­ing con­trolled com­pletely elec­tron­i­cally, the con­troller does not cy­cle con­tin­u­ously in a loop: once you have reached RCA-4, you have to counter-ro­tate the con­trol to ac­cess the other in­puts. You can re­name all th­ese in­puts if you like, though you’re lim­ited in the num­ber of char­ac­ters you can use for each one.

The dis­play also al­lows you to check how many hours are on the valves, whether you’ve set the pream­pli­fier for mono or stereo op­er­a­tion (as well as set it for ei­ther!), and in­di­cates whether you’ve ad­justed the bal­ance of the left and right chan­nels away from the de­fault (0dB) for each. All of th­ese op­er­a­tions are ac­cessed by fairly ar­cane pro­cesses that in­volve al­ter­nately press­ing and turn­ing the con­troller dial: This is a bit tricky to mas­ter, but strangely sat­is­fy­ing once you have. The rotary vol­ume con­trol is par­tially re­cessed into the front panel and its range of ac­tion can be mod­i­fied us­ing the small tog­gle switch to its left, which of­fers a choice of gain modes (0dB or +12dB).

Just to the right of the vol­ume con­trol is a small tog­gle switch to select which of the Clas­sic Preamp’s out­puts you want to use: XLR (bal­anced), RCA (un­bal­anced) or the head­phone socket on the front panel. The only is­sue I had with this arrangement is that if your head­phones are in­ef­fi­cient you’ll have to turn the vol­ume up when lis­ten­ing to them, which means you’ll have to be very care­ful to make sure you turn the vol­ume down be­fore re­set­ting the switch to ei­ther the XLR or RCA po­si­tion, oth­er­wise you’ll blast your speak­ers with high-vol­ume sound. Al­though the head­phone socket looks quite un­usual, it’s a stan­dard 6.5mm stereo socket—it just has a pro­trud­ing shroud around its pe­riph­ery.

The large con­trol to the right of the vol­ume con­trol is a power switch… well, ac­tu­ally, it’s more than a power switch. In ad­di­tion to us­ing it to turn the Clas­sic Preamp on and off, it also se­lects ‘Mute’ plus has a spe­cial po­si­tion ( R ) to which it has to be switched if you want to use one or more of the sev­eral dif­fer­ent re­mote con­trols that are avail­able to con­trol Na­gra com­po­nents.

Al­though the Clas­sic Preamp can be con­nected di­rectly to the 240V mains, it can be op­tion­ally pow­ered by an ex­ter­nal power sup­ply, such as the Na­gra MPS (Mul­ti­ple Power Sup­ply) or the Na­gra ACS II. One rea­son for us­ing the MPS might be to pro­vide to­tal iso­la­tion from the mains power sup­ply, be­cause the MPS can be fit­ted with an Li-Ion bat­tery.

Also avail­able for the Na­gra Clas­sic Preamp are op­tional in­put and out­put trans­form­ers (hand-wound in-house by Na­gra) to cre­ate a fully sym­met­ri­cal float­ing sig­nal.

NA­GRA CLAS­SIC AM­PLI­FIER

Na­gra’s Clas­sic am­pli­fier can be user-con­fig­ured ei­ther as a stereo power am­pli­fier, in which con­fig­u­ra­tion it’s rated by Na­gra as hav­ing an out­put of 100-watts per chan­nel into 8 , or as a mono power am­pli­fier, in which mode it’s at­trib­uted with a 200watt out­put power rat­ing.

The single bar con­trol switch on the front panel of the Na­gra Clas­sic power am­pli­fier has po­si­tions for ‘Off’, ‘Auto’, ‘Mute’ and ‘On’. The ‘Auto’ set­ting en­ables the Clas­sic to switch it­self in and out of Standby mode, so it switches it­self ‘On’ when it de­tects an au­dio sig­nal at its in­put and ‘Off’ when no sig­nal has been de­tected for a pe­riod of time.

Na­gra’s dis­tinc­tive mov­ing-ar­ma­ture mod­u­lome­ter makes an ap­pear­ance here as well, though in this case it’s a ‘dou­ble mod­u­lome­ter’ be­cause the me­ter has two nee­dles rather than just the one. The black­tipped nee­dle shows the out­put of the left chan­nel and the red-tipped nee­dle shows the out­put of the right chan­nel. There are dif­fer­ent cal­i­bra­tions for stereo op­er­a­tion into 8 loads and for mono op­er­a­tion into 8 loads. To the right of the mod­u­lome­ter is a mo­men­tary-ac­tion tog­gle switch that can be used to dim the dis­play light­ing through six lev­els or turn it off com­pletely.

Al­though the dou­ble mod­u­lome­ter can be a guide to how much power is go­ing to your loudspeakers, the nee­dles’ re­sponse time is not fast enough to show if the am­pli­fier goes into clip­ping (which and am­pli­fier will do if you ac­ci­den­tally over­drive it), so Na­gra has help­fully in­cluded a chameleon LED that flashes when the am­pli­fier goes into clip­ping to alert you to turn the vol­ume down. It flashes yel­low when mo­men­tary clip­ping is de­tected (which is harm­less and usu­ally un­de­tectable by the hu­man ear) and flashes red when con­tin­u­ous clip­ping is de­tected (which will cer­tainly be au­di­ble and could cer­tainly harm your speak­ers if al­lowed to per­sist). In cases where con­tin­u­ous out­put stage clip­ping is de­tected, the LED doesn’t merely glow red, the am­pli­fier will also au­to­mat­i­cally shut it­self down to pro­tect both it­self and your loudspeakers.

The rear panel has both bal­anced (via gold-plated XLR) and un­bal­anced (via gold-plated RCA) in­puts, with a tog­gle switch to select be­tween them. The sen­si­tiv­ity of each in­put can be ad­justed be­tween 1V (for rated out­put) and 2V (for rated out­put) us­ing a tog­gle switch. The am­pli­fier can also be set (us­ing a three-way tog­gle switch) for ‘Bi-amp’, ‘Nor­mal’, or ‘Bridged-mode’ op­er­a­tion. Na­gra has very sen­si­bly re­cessed all th­ese tog­gle switches so there is no pos­si­bil­ity of mov­ing one ac­ci­den­tally. Re­mote in/out ter­mi­nals and an earth ter­mi­nal are also fit­ted.

Only a single set of speaker out­puts is fit­ted, us­ing rather un­usual high-cur­rent con­nec­tors made by French firm Car­das,

where a single screwed fit­ting tight­ens the posts of both pos­i­tive and neg­a­tive speaker ter­mi­nals si­mul­ta­ne­ously. Whilst ad­mir­ing the fa­cil­ity of this clamp­ing sys­tem, it best suits those whose speaker ca­bles are ter­mi­nated with ei­ther spade or ring con­nec­tors. How­ever, if you are not us­ing the am­pli­fier in bridged mode (in which case you should not in­stall the ‘bridge links’ sup­plied into the ap­pro­pri­ate places on the rear panel) you can use th­ese bridge link ‘holes’ to insert speaker leads ter­mi­nated in ba­nana plugs.

So far as the in­ter­nal cir­cuitry of the Na­gra Clas­sic is con­cerned, both the power sup­ply and the out­put stage are lin­ear, with the out­put stage us­ing a single pair of MOSFET out­put de­vices in each chan­nel that Na­gra says: ‘ op­er­ate in pure Class-A over a very large power band and be­yond in Class-AB.’ Us­ing only a single pair of out­put de­vices is fairly un­usual in a high-power am­pli­fier, but Na­gra says it has a rea­son for this ap­proach: ‘ Gen­er­ally, as­sem­bly of an equiv­a­lent out­put stage re­quires sev­eral pairs of tran­sis­tors, which is dif­fi­cult to achieve pre­cisely,’ says the com­pany. ‘ The sim­plic­ity of the Clas­sic Amp’s de­sign is the key to its mu­si­cal­ity.’

IN USE AND LIS­TEN­ING SES­SIONS

Al­though the Clas­sic Power amp is al­ways ready to go from the get-go, the Clas­sic Preamp has to be warmed up for op­ti­mal per­for­mance, which takes around four min­utes de­pend­ing on the am­bi­ent tem­per­a­ture in the room. Be­cause you can’t see the valves, Na­gra’s front dis­play shows the word ‘Heat­ing’ while the valves are do­ing that… very help­ful! Be­cause the Clas­sic Preamp does use valves, I would rec­om­mend that you turn it off when­ever you’re not us­ing it, in or­der to ex­tend the life of the valves. Na­gra reck­ons that if you leave the am­pli­fier on all the time the valves will last for at least 5,000 hours and that get­ting 10,000 hours from the valves ‘is not un­usual’. My ad­vice is do the maths, price the cost of re­place­ment valves and de­cide how you want to play it. Per­son­ally, I’d switch it off when­ever I wasn’t us­ing it, and have the Clas­sic Amp set for ‘Auto’ op­er­a­tion.

I dis­cov­ered one op­er­a­tional trap for young play­ers right at the out­set, which came about be­cause of my habit of mut­ing com­po­nents when switch­ing from one in­put to an­other in or­der to avoid switch­ing tran­sients. That trap is that when Na­gra’s Clas­sic Preamp is switched to ‘Mute’, the in­put se­lec­tor is dis­abled, so you can’t switch in­puts. I can can see the sense in this, be­cause it means you can’t ac­ci­den­tally switch from a source com­po­nent with a low-volt­age out­put to one with a high-volt­age out­put (po­ten­tially get­ting an un­wanted blast of high-vol­ume sound), but I still found it a bit quirky.

Right from the very first notes that is­sued from this Na­gra combo I was hooked by their sound. Those notes were from one of Joni Mitchell’s un­der­rated clas­sics, ‘For The Roses’ from ‘way back in 1972 (not that I was around to hear it when it was first re­leased… I’m a late-comer to Mitchell’s art, but am now a card-car­ry­ing fol­lower.) The Na­gras made the son­ics on this al­bum to­tally co­he­sive, weav­ing all the strands into a seam­less and to­tally sat­is­fy­ing whole. The clar­ity of the sound I was hear­ing when I lis­tened was rev­e­la­tory, one great ex­am­ple be­ing the echo to Mitchell’s voice on Blonde in the Bleach­ers, which sounded more real than I’ve heard it from most other am­pli­fiers. Russ Kunkel’s in­tro on drums is a sear­ing, sonic blast… won­der­ful! Then there’s the sound of Mitchell’s piano on Les­son In Sur­vival, which is first a les­son in how Na­gra’s ‘keep it sim­ple’ ap­proach to am­pli­fier cir­cuitry pays off in im­proved son­ics and mu­si­cal­ity, and sec­ond a re­minder that a great many of the record­ings made back in the 1970s are beau­ti­fully clean and won­der­fully dy­namic and ‘way better than those that are be­ing made to­day, de­spite the so-called ‘im­prove­ments’ in tech­nol­ogy. (Dig­i­tal Au­dio Work­sta­tions have a lot to an­swer for, IMHO.) Just lis­ten to the string sound of the piano on this track… it’s sen­sa­tion­ally au­then­tic. It’s a wonder to me why For The Roses isn’t in ev­ery­one’s li­brary, though one rea­son may be it’s one of those al­bums that has to be lis­tened to from start to fin­ish for it to make sense—it’s a story with 12 chap­ters—yet strangely enough, its best-known track, You Turn Me On, I’m A Ra­dio, was in­cluded solely to try to get air­play for the al­bum, so it’s re­ally the odd track out, and you’re prob­a­bly better off to skip it.

The Na­gras’ abil­ity to con­vey dra­mat­ics was demon­strated to me when play­ing Maya Frid­man’s arrangement for piano and cello of Prokofiev’s oc­cult opera ‘The Fiery An­gel’ (TRPTK TTK 0009). On this ver­sion she plays a 200-year-old cello and her col­lab­o­ra­tor, Artem Be­l­ogurov, an 1880 Erard. The Na­gras reveal the darkly wooden sound of the old Erard to great ef­fect—you can eas­ily hear how com­pletely dif­fer­ent it is from that of a mod­ern grand piano. The sound of Frid­man’s cello is also won­der­fully re­pro­duced by the Na­gras, and you can be cer­tain you haven’t heard the cello sound so many ways be­fore in the one work… it’s as if Frid­man has de­lib­er­ately in­cluded ev­ery play­ing tech­nique she could. Don’t let the ‘opera’ bit put you off, by the way, this work is ab­so­lutely hyp­notic… you won’t be able to stop lis­ten­ing.

I found the clar­ity and il­lu­mi­na­tion the Na­gras gave to the re­pro­duc­tion of the midrange worked par­tic­u­larly well when I was au­di­tion­ing choral works, such as Mozart’s fa­mous ‘Re­quiem’ where I could sep­a­rate out in­di­vid­ual singers from the choir and even po­si­tion them across the sound­stage. When the choir was in full voice, the sense of scale and rich­ness of sound from the Na­gras lit­er­ally sent chills down my spine. I truly love this work, and to me it mat­ters not who ac­tu­ally wrote it, be­cause no-one is cer­tain who did… but one thing about which we can all be ab­so­lutely cer­tain is that it made Count Walsegg-Stup­pach more fa­mous than he ever would have been if he hadn’t fi­nanced it, so his hun­dred ducats were well spent!

I tested out the Na­gras’ abil­ity to de­liver grunge at the high­est pos­si­ble vol­ume lev­els with what I think is one of the best heavy-metal tunes ever writ­ten—Black Sab­bath’s Para­noid. No prob­lems what­so­ever… the duo per­formed like the pro­fes­sion­als they are! The mod­u­lome­ters on both the preamp and the power amp were flail­ing around like the ba­ton of a crazed con­duc­tor, and the vol­ume was such that I was fear­ing for the safety of my loudspeakers, but de­spite this I could not hear even the slight­est inkling of any com­pres­sion or dis­tor­tion… and yes, that yel­low LED was blink­ing.

CON­CLU­SION

The name Na­gra has been syn­ony­mous with high-per­for­mance pro­fes­sional au­dio equip­ment ever since the com­pany de­vel­oped the first pro­fes­sional recorder more than 60 years ago. Since then the per­for­mance of Na­gra’s pro­fes­sional com­po­nents has gained the com­pany three Os­cars and an Emmy.

Read­ers in­ter­ested in a full tech­ni­cal ap­praisal of the per­for­mance of the Na­gra Clas­sic Preamp and Na­gra Clas­sic Amp should con­tinue on and read the LAB­O­RA­TORY RE­PORT pub­lished on the fol­low­ing pages. Read­ers should note that the re­sults men­tioned in the re­port, tab­u­lated in per­for­mance charts and/or dis­played us­ing graphs and/or pho­to­graphs should be con­strued as ap­ply­ing only to the spe­cific sam­ple tested.

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