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Krell KSA 50 I-II -S – Power Amplifier – 2x50W Classe A

Krell KSA 50 manifesto

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Krell KSA 50 – Power Amplifier – 2x50W Classe A


Power Amplifier – 2x50W Classe A

La veste estetica, molto sobria ed elegante, è caratterizzata da un frontale in alluminio spazzolato di colore grigio chiaro per la pima versione e ………


 By Anthony H. Cordesman John Atkinson • Posted: Sep 9, 2007 • Published: Sep 9, 1985



Il Video del Vintage HiFi Club

Krell KSA 50

Quote: eur 1.500 / 2.000 (per un esemplare in perfetto stato e completo di manuale e imballo originale)


 Krell KSA 50 II front

 Krell KSA 50 II


Il Krel KSA 50 è un amplificatore stereofonico un pura Classe A prodotto nel 1980.

Krell KSA 50  . La veste estetica, molto sobria ed elegante, è caratterizzata da un frontale in alluminio spazzolato di colore grigio chiaro per la pima versione e di colore antracite chiaro per la versione MKII. In entrambi i casi la parte anteriore è caratterizzata da due poderose maniglie dello stesso colore del pannello, molto utili per il trasporto dell’ampli, dato il considerevole peso di questa macchina. La parte posteriore anch’essa estremamente semplice: raccoglie in alto i pin RCA per il segnale, mentre sotto sono posizionati i morsetti per i collegamento dei diffusori. Infine, al centro in basso c’è la vaschetta IEC per l’alimentazione e accanto un dispositivo che consente la messa in mono. Altre due maniglie completano il pannello posteriore.


Krell KSA 50 II back

 Krell KSA 50 II back


L’interno, molto ben ingegnerizzato, accoglie al centro le alette di raffreddamento dei transitor finali, oltre ad una ventola posta alla base. Nel restante spazio ci sono i generosi trasformatori di alimentazione con i condensatori. La cablatura è essenziale e di buona fattura.

L’ultima versione del KSA 50, denominata S, ha un loock più moderno con maniglie rettangolari che incorniciano il frontale e alette di raffreddamento esterne. Sul posteriore sono disponibili ingressi con connessioni bilanciate.


krell ksa 50 s

 Krell KSA 50 S



Fin dalla sua uscita, questo finale, è stato molto considerato grazie ad un suono dettagliato, chiaro e molto musicale. Nonostante i suoi 50W soltanto, questo finale Krell è capace di gestire casse piuttosto difficili e se non viene portato oltre il limite della capacità di erogare corrente, offre prestazioni di pregio assoluto. In particolare la versione MKII, forse la più equilibrata, ha doti di correttezza timbrica molto evidenti, con una gradevolissima gamma alta dal timbro chiaro, una gamma media aperta e una gamma bassa ben frenata.


krell ksa 50 II inside Krell KSA 50 II inside


Ancora oggi, se messo a confronto con elettroniche di elevato livello, mostra le qualità che ne hanno fatto un piccolo mito. Molti addetti ai lavori, me compreso, lo considerano uno dei 10 migliori amplificatori mai costruiti.

Oggi, se consideriamo il prezzo a cui si può acquistare e se trovato in condizioni perfette, è uno oggetto quasi irrinunciabile.


Vintage HiFi Club

Massimo Piantini


Sophos pubblicità sequenza 1 640x117




Krell KSA 50 I

Krell KSA-50 power amplifier

By Anthony H. Cordesman John Atkinson • Posted: Sep 9, 2007 • Published: Sep 9, 1985

Some readers may feel that it is pushing poetic license beyond reasonable limits to call the Krell KSA-50 a “new-wave” amplifier. It has, after all, been around for several years. The Krell KSA-50 is new-wave enough, however, to be an incredibly stiff class-A design, rather than a pseudo–class-A circuit, and its 50 watts per channel are supported by enough of a power supply to drive an arc welder. You get about 70 watts of RMS power with 8 ohms, 150 watts with 4 ohms, and sufficient watts into 2 ohms to threaten my load resistors. There is almost enough power to drive a pair of Apogee Scintillas at their ohm setting—though I’d prefer at least the Krell KSA-100.



 Krell KSA 50 I back

The timbre of this amp is sufficiently neutral and uncolored that there just isn’t much to say about bass, midrange, and treble. They will tend to reflect the input signal and interconnects rather than the amplifier. I can say that you will want to use interconnects like the Straight Wire, Distech, and Randall rather than the Monster and MIT, and that the amp seems to work best with a dynamic cartridge possessing a slightly live midrange, like the Koetsu Black Gold or the Kiseki Purple. This, however, brings me to the sound qualities of the Krell KSA-50 that are truly unique.

Like most of the better class-A amplifiers I’ve heard, the Krell KSA-50 sounds liquid rather than dynamic. While no two class-A amplifiers ever sound alike, they all share a kind of mid-hall sound. Rather than give you “exciting” sound with a great deal of “forward” dynamic energy, they seem rather to disappear into the music. The Krell does this more than any class-A amplifier I’ve heard. I suspect this is because of the Krell’s ability to deliver strong bass into virtually any speaker load, something for which most class-A amps lack the power, and because the designer (Dan D’Agostino) has gone to great pains to remove the last trace of hardness from the upper octaves…….. See More

Description: Solid-state stereo power amplifier.

Maximum power output: 50W into 8 ohms (17dBW), doubles with each halving of load impedance down to 1 ohm.
19″ W by 9″ H (including feet) by 19″ D (including handles). Weight: 60 lbs (net).
Serial number of unit tested: not noted.
Price: $1900 (1995); no longer available (2007).
Manufacturer: Krell Industries, Milford, CT 06460 (1985); Krell Industries, 45 Connair Drive, Orange, CT 06477. Tel: (203) 799-9954. Fax: (203) 799-9796. Web:







krell ksa 50 S Front 2

  Krell KSA 50 S

Krell KSA-50S power amplifier

By John Atkinson • Posted: Aug 2, 1995

In the fall of 1982, I had just become the Editor of the English magazine Hi-Fi News & Record Review. Hi-fi was in a state of flux. The Compact Disc had just made its debut in Japan, but the British and American launches were six months and a year away, respectively. The Linn orthodoxy prevailed about the role of the source in system performance, but there was no agreement about what was and was not important when it came to enhancing the musical experience. “Objectivists” insisted that amplifiers and even loudspeakers had pretty much reached a design plateau where no further improvement was necessary or even desirable, while “subjectivists” were fragmented. All I was aware of was that my system, based on Celestion SL6 loudspeakers, needed more of an undefinable something.


krell ksa 50 S back 2

  Krell KSA 50 S back


Then I tried a modestly powered, hot-running class-A amplifier, the KSA-50, from a new US company: Krell Industries. (The company was modestly named after the legendary super race in the classic 1956 SF movie, Forbidden Planet: “You fool! To think that your ape-brain can contain the full knowledge of the Krell!” exclaimed the marooned Dr. Morbius when he found one of his human intruders dying after trying the Krell mind amplifier.) …. See More



Krell KSA 50 s inside

   Krell KSA 50 S inside


Krell KSA-50S power amplifier Specifications

Description: Solid-state stereo power amplifier. Specified output power: 50W into 8 ohms (17dBW), doubles with each halving of load impedance down to 1 ohm. Maximum output voltage: 75.8V peak to peak, 26.8V RMS. Maximum output current: 60A. Frequency response: not specified. Distortion: <0.018% at 1kHz; <0.18% at 20kHz, full power. Signal/noise ratio: >100dB. Input sensitivity: 1.34V RMS. Gain: 26dB. Input impedance: 47k ohms.
Dimensions: 19″ W by 14.25″ D by 8.5″ H. Weight: 52 lbs (net).
Serial number of unit reviewed: 31-10530.
Price: $3300. Approximate number of dealers: 43. Warranty: 5 years, parts and labor.
Manufacturer: Krell Industries, 45 Connair Dr., Orange, CT 06477-0533. Tel: (203) 799-9954. Fax: (203) 799-9796. Web: .








Krell KSA 50 II logo

I own since a long period 3 marvelous amplifiers. One THRESHOLD SA/3.9 upgraded, one KRELL KSA 50MKII and a pair of JADIS JA80.
Today, we are reviewing the KRELL.

This one is the second generation of the KSA product line.
It comes from the first serie “KSA” from KRELL. This serie works fine like the 2 following ones, KRS and KAS. Do not take any of the other series, as you would be disappointed !…….. See More


krell ksa 50 II 2

   Krell KSA 50 II




Well, I posted before about my itch to try the Krell KSA-50S in my system and I finally had my chance today. To summarize, I love the way this ‘little’ Krell sounds so far…. sweet, transparent, fast, with excellent bass depth, detail, and snap. More later.

Someone commented that the KSA-50S is not ‘true class A’ biased like the older KSA-50. Well it is but it’s done more intelligently with something Krell calls Sustained Plateau Biasing. And I like it because the unit doesn’t draw huge amounts of power constantly like most basic full class A biased designs (like my old Pass Aleph that I once owned). Instead, it runs barely warm at idle but heats up and draws lots of power only while you’re actually using the amp. When the signal goes away, the amp automatically goes back to a cool running standby mode.


krell ksa 50 S 3

   Krell KSA 50 S

I took some measurements while obseriving the Sustained Plateau Bias feature in action. It’s not a gimmick. It’s practical and I like the way it works. There are three modes: Standby, Bias Level 1, and Bias Level 2. The LED indicators on the front panel tell you which Bias level you’re operating at…… See More






krell ksa 50 I inside 3

  Krell KSA 50 I inside



krell ksa 50 I indide 1

  Krell KSA 50 I inside



krell ksa 50 I 2

  Krell KSA 50 I inside




krell ksa 50 I back 2

  Krell KSA 50 I back



krell ksa 50 I back


  Krell KSA 50 I





krell ksa 50 system 3

Krell KSA 50 System




krell ksa 50 systems 2

Krell KSA 50 System + Quad ELS 57



krell ksa 50 systems 3

Krell KSA 50 System + Linn Isobarik



krell ksa 50 systems

Krell KSA 50 System



ML Manifesto Sequenza 11 1.0 sec con dissolvenza





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