Pre/Power Amplifiers

Otherwise, a menu option lets the user configure details such as balance, input trims and labelling, and bypass (for use with a surround processor), although this isn't helped by the narrow vertical viewing angle of that display. Otherwise this is a very simple, if solidly engineered preamp, designed and built in typical Krell style. It uses the company's balanced Current Mode circuit design, and has a massive power supply for a preamp, employing a 95VA transformer and 40,000µF of capacitance. The headphone output is fed directly from the line stage for high-quality personal listening.

Power Of The Krell
The Illusion II and KSA-i400 were slotted into PM's reference system between the usual Aurender W20SE/dCS Vivaldi ONE APEX front-end [HFN Mar '23], the latter running with a fixed output purely as a DAC, and Bowers & Wilkins' 801 D4 Signature speakers [HFN Sep '23]. The power amp was set on the floor between the speakers and connected with long balanced cable runs of Transparent cable to the preamp, much as I suspect most users will use this hefty lump of electronics – it's the classic 'long interconnect/short speaker cables' US audiophile set-up.

In use, two things are striking about the Illusion II/KSA-i400 combination: one is that it seems to have almost limitless power, which suits the somewhat demanding Bowers & Wilkins flagship speakers exceptionally well. The other is that the amps need to be cranked a bit to come to life, sounding less animated at very low levels. This isn't unusual, as most systems sound better when they're shifting some air, but PM's Lab Report does show a change in distortion 'fingerprint' until the power amp is flexing its muscles with a double-digit watt output. Coincidence?

Snap And Punch
However, in practice it doesn't take much to get into this 'sweet spot'. With the jangly sound of Ali Farka Touré's Voyageur set [World Circuit WCD097], the Krell pairing delivers excellent snap on the guitar strings, plenty of vocal character, and percussion that's crisp and, where appropriate, weighty. Maybe a little more warmth and intimacy wouldn't go amiss, but there's no problem with the focus on the performances here and in the high levels of detail revealed with Penguin Café's latest set, Rain Before Seven [Erased Tapes Records ERATP159CD].

From the repeating patterns of 'Might Be Something', with real conviction in the double bass, to the more mystical 'Galahad', there's fine insight into the scoring and performances. Soundstaging is excellent too, giving a real 'listen in' effect with the 801 D4 Signatures. The sound is also fast and driving with the dance rhythms of the concluding track, 'Goldfinch Yodel'.

The KSA-i400 does scale with almost disdainful ease, for example with Rush's live 'The Spirit Of Radio' from the remastered Moving Pictures [Mercury Records download], where the amplifier unleashes serious punch. Bring things down to the studio-recorded 'Red Barchetta' from the same set and there's no shortage of detail, particularly in Neil Peart's precision drumming. It almost goes without saying that the KSA-i400 will go as loud as anyone could sensibly want without any suggestion of stress.

Rock The Room
Those characteristics also suit well Nicolas Kynaston's recording of Liszt's 'Prelude and Fugue on B.A.C.H' on the Royal Albert Hall 'Father Willis' organ [from Base 2 Music 012; www.nativedsd.com].

Encoded from an original 1968 analogue tape, this release has monumental power, and that real sense of the massive instrument shaking the entire venue comes through the big Bowers & Wilkins speakers driven by the Krell KSA-i400. From the subtle intricacies of the higher manuals through to the great growling low frequencies, it was all delivered with an almost palpable sense of the size of the venue being driven by the organ.

Go poppy with the recent remaster of the dance mix of Human League's 'Don't You Want Me', from Dare Singles & Remixes [UMC download], and while this seven-plus minute version is a definite period piece, it's still anthemic. The KSA-i400 powers through the lengthy stripped-down drums and bass intro, basically laying out the whole backing track before the more familiar aspects of the song swing in with those big bass chords. Crank it up, and even if it really is a guilty pleasure, above all else it's huge fun.

The same could be said for Bonobo's take on London Grammar's 'Hey Now', from the recent The Remixes compilation [Ministry of Sound download]. As one might expect given the remixer's own releases, such as those on Fragments [Ninja Tune ZENDNL 279], this one is infused with some serious electro/drum and bass. The KSA-i400 really gets the 801 D4's big bass drivers moving, albeit under strict control, delivering maximum low-end impact without detracting from all the interesting stuff going on above. Maximum information, maximal drive – it's what these Krell amps do best.

A Touch Of Romance
That's not to say this big, powerful amplification can't do subtle. Fed with an atmospheric solo piano recital such as Sergei Kivitko's Schubert By Candlelight [Fresh! FR753; 96kHz/24-bit], recorded live in front of an audience in Madrid, the Krell combo not only brings out the scale of the piano in a finely delineated acoustic, with wonderful dynamics, but also does an excellent job with the intimate, romantic atmosphere of the entire performance. All told, this was a rather fine relaxing evening listen, emphasising the all-round ability of these pre/power amplifiers.

The combination of power and finesse is also deployed to great effect in Michala Petri's recording of Ma Shuilong's 'Bamboo Flute Concerto' on her Chinese Recorder Concertos [OUR Recordings 6220603], bringing out the album's fine balance between the delicate solo instrument and the power of the Copenhagen Philharmonic. Altogether, the performance sounds as thrilling as it is exotic.

But then that's the story with this Krell preamp and mighty power amp – there's the insight to elevate the quality of recordings and performances alike, with colossal reserves not just to drive speakers convincingly, but also control them as they deliver with speed, definition and focus. It's a classic 'iron fist/velvet glove' amplifier pairing, well suited to an extremely wide range of musical genres, loudspeakers and listening tastes.

Hi-Fi News Verdict
OK, so it takes a bit of level before this Krell power amp gets into its stride, and at late night background levels it can even sound a shade passive, but give it its head and it combines with the relatively simple Illusion II preamp to deliver a compelling, satisfying sound that's as informative as it is hard-charging. Behind all that high-level swagger is a design as much about micro-dynamics and detail as it is a wall-shaker.