Outstanding Product Award - Hi-fi News Magazine
"A Beast of an Amp"
Building on the success of the award-winning S-300i integrated amplifier, the S-550i from Krell Industries boasts the sound quality and power output capable of driving any loudspeaker to its maximum performance. Delivering 275 watts of stereo output, the S-550i is a power source for virtually any speaker on the market while occupying a fraction of the space typically required for a system delivering this sound quality.
"Without hesitation, I nominate the s-550i as a perfect choice for those who want unbridled power yet will not or cannot house two components," reports Ken Kessler in the July 2013 issue of England's Hi-fi News magazine, which honored the Krell an Outstanding Product Award. "It is a beast of an amp."
"Its Performance is Incredible"
"The S-550i is solid, rugged and reliable," raves Jim Clements in a March 5, 2014 review for Secrets of Home Theater and High Fidelity. "Its performance is incredible in both the listening tests and on the bench tests. It has high bandwidth and low measured distortion especially considering it has no global negative feedback in the preamp stage."
"Despite its relatively compact dimensions, the amplifier packs a 1750W transformer and generous power supply capacitor storage, and the power section again uses all-discrete circuitry, and like all of the company's power amps is designed as an ideal voltage source, doubling output as speaker impedance halves," reports Andrew Everard in England's What Hi-fi? magazine, March 14, 2013.
Outstanding Feature Set
The S-550i is outfitted with balanced and single-ended inputs, iPod dock, and Theater Throughput™ mode. Developed by Krell, Theater Throughput simplifies integration into home theater systems. For custom integration applications, 12-volt triggers, RS-232 connectivity and rack mount ears are included. Operational parameters can be customized via the menu system that is accessible from the front panel or the included brushed Aluminum remote control.
Trickle-down Technology from Phantom
The preamplifier section features circuit concepts from Krell's flagship Phantom preamplifier. Krell Current Mode provides unequaled bandwidth for the most revealing playback of today's high resolution music sources. Direct coupled circuitry eliminates impact-robbing capacitors from the signal path and an elegant, custom-machined level control adjusts volume.
Discrete circuitry, in a balanced topology, is afforded its own power supply regulation. All signal gain is realized using surface mount technology featuring proprietary current mirrors with nearly 500 times the open loop linearity of other designs. Negative feedback is not used anywhere in the preamplifier, nor is it necessary. Open-loop distortion is typically less than 0.003%. The volume control is realized with a balanced resistor ladder - bandwidth and transient response of the preamp circuitry are virtually unaffected by the volume setting.
Massive Power Transformer
The S-550i packs a massive 1,750 watt transformer and 68,000μF of capacitance into an elegant 5" high chassis. This power supply feeds classic Krell circuitry throughout the topology using only discrete circuitry.
As with all Krell amplifiers, the S-550i design is an ideal voltage source. That is, the S-550i doubles its power output when a speaker's impedance is halved. For the S-550i, the results are 275 watts into 8 Ohms and 550 watts into 4 ohms. This capability is essential for realistic reproduction of a recording's dynamic content. Most amplifiers can't deliver this power doubling, leaving music sounding compressed and lifeless.
Specifications for Preamplifier Only
Outstanding Product Award - Hi-fi News Magazine
"Without hesitation, I 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, such that I think I've found something currently available to drive even Scintillas. Yes, that kind of beast."
- Ken Kessler, Hi-fi News, July 2013
"The S-550i is solid, rugged and reliable. Its performance is incredible in both the listening tests and on the bench tests. It has high bandwidth and low measured distortion especially considering it has no global negative feedback in the preamp stage."
"On listening, the sound is vibrant, dynamic and dimensional. Pure Americana in so many ways… A high damping factor means it will grab your speakers by the cajones and never let go. Plus it puts out huge amounts of power with high current capability and the ability to double down when the load is halved. This is where the passion, drive and delicacy are unleashed from you favorite music. Don't forget that the S-550i handles cinema well; so deeply quiet when required and so ruthlessly gripping when demanded. A very solid all-around performer that really is capable of driving just about any speaker I can dream of."
- Jim Clements, Secrets of Home Theater and High Fidelity, March 5, 2014
"Despite its relatively compact dimensions, the amplifier packs a 1750W transformer and generous power supply capacitor storage, and the power section again uses all-discrete circuitry, and like all of the company's power amps is designed as an ideal voltage source, doubling output as speaker impedance halves."
- Andrew Everard, What Hi-fi? magazine, March 14, 2013