Krell S 550i (£4998)

Without hesitation we nominate the S-550i as a perfect choice for those who want unbridled power yet will not (or cannot) house two components

The Editor’s review briefing included the warnings: ‘It’s 29kg – you may need help in unpacking it’ and ‘The S-550i is a remarkably dense amplifier, probably the most self-effacing yet monstrously powerful integrated we’ve ever tested.’

This new flagship integrated, replaces the FBI while the S-300i remains as Krell’s entry-level integrated at £2795. The S-550i is a true ‘big brother’: the sonic resemblance is uncanny save for a brutal power delivery.

While the front panel suggests minimalism, that’s only because all minor settings are relegated to a menu system, eg, balance setting and input trim, which can also be accessed by the full-function remote. The S-550i’s fascia offers source select, volume, mute, power on/off (from standby) and a menu display. Inside is circuitry that recalls the S-300i and a preamplifier section that can be used on its own via a pair of phonos at the back.

The design reflects long-standing Krell practice, with the company’s proprietary Current Mode technology, discrete direct-coupled circuitry in a balanced topology, and individual power supply regulation. Much of the weight is attributable to a massive 1750W toroidal transformer that shifts the weight of the amp toward the front.

Other circuit details include: no negative feedback; a balanced resistor ladder gain control; one set of balanced XLR inputs along with four single-ended phonos; plus a dedicated iPod/iPhone dock (supplied by Krell).

Aside from a worrying switch-on thump, the S-550i is easy to set up. We used it with an iPod Classic, the Marantz CD-12/DA-12 in balanced mode and Wilson Audio Sophia 3s.

Nothing taxes it

This amp can swing from soft to loud with the graceful progress of a Bugatti Veyron’s W16 climbing to its kilo-ponies. We began with Eleanor McEvoy’s ‘God Only Knows’ from If You Leave… [Moscodisc], needing to learn if the Krell could handle delicacy as well as it would, without question, cope with headbanging abuse. No brutality, no coarseness, no lack of finesse: the S-550i placed Ms McEvoy in the room, her piano tinkling and resonating with the realism we’d take for granted from the Audio Research REF75, in all its tube-y glory. This was a solid-state amp free of the brittle, of the glassy, of the jarring.

Much as we wanted to stick to that disc, we couldn’t resist the edgy, scorching axemanship of Johnny ‘Guitar’ Watson’s ‘I Need It’, two-and-a-half-minutes in, and preceded by punchy horns and a percussion opening that surely must have been sampled by seven-figures’ worth of copyists. The stand-out from 1976’s Ain’t That A Bitch [Sequel NEM CD 774], it features staccato playing so evocative of that era, all Superfly and wide lapels and huge shades.

Punch, attack, crisp edges, no decay – the Krell managed every sweep of brush on cymbals, the fast plucking with a hyper-metallic edge. And yet the next track, ‘I Want To Ta-Ta You Baby’, was pure, liquid blues – still with the cutting snap of the strings, but slithery, salacious, smoky. A perfect horn section, mixing long, airy sighs with decisive punctuation, the Krell arrayed it behind Watson, creating a backdrop with the curve of Venus’s shell, but wider and taller. It was a perfect, seamless, wall of sound.

One of the most intensely tortured songs we’ve ever savoured from the country milieu is Conway Twitty’s sublime ‘It’s Only Make Believe’: we were delighted to find it on Glenn Campbell’s Collection [EMI Gold]. It builds to an intensity that is almost disturbing, a mass of instruments and grandiose voices. Campbell soars, the key changes lifting him up, up, up to a point where you think his voice just has to crack. It doesn’t. Neither does the Krell S500i. The form, the scale, the sheer power were so-oo capably, competently resolved…


There have been massive integrated amplifiers in the past but without hesitation we nominate the S-550i as a perfect choice for those who want unbridled power yet will not (or cannot) house two components. It is a beast of an amp: one that might drive even the old Scintillas.

Originally published in the 2013 Yearbook