The Krell S-550i builds on the success of the S-300i integrated amplifier and delivers 275 watts of stereo output. The S-550i is outfitted with balanced and single-ended inputs, iPod dock, and Theater Throughput™ mode. 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.
The preamplifier section features circuit concepts from Krell’s flagship Phantom preamplifier. Direct coupled circuitry eliminates capacitors from the signal path and a 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. Negative feedback is not used anywhere in the preamplifier. 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.
The S-550i packs 1,750 watt transformer and 68,000μF of capacitance into a 5″ high chassis. This power supply feeds classic Krell circuitry throughout the topology using only discrete circuitry. 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.