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Krell S-550i Integrated Amplifier

Krell S-550i Integrated Amplifier

Krell just released the S-550i Integrated Amplifier, which upgrades the performance of their S-300i integrated amp. The new S-550i delivers 275-watts of output, with balanced and single-ended inputs, iPod dock, and Theater Throughput mode to simplify 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.

Preamplifier Highlights
The preamplifier section features circuit concepts from Krell’s flagship Phantom preamp. 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.

Krell S-550i Integrated Amplifier - back

Power Amplifier Highlights
The S-550i packs a massive 1,750 watt transformer and 68,000?F 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 both channels driven. 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.

Price and Availability
The Krell S-550i Integrated Amplifier is available now for $5,000 in silver and black finishes.


1 pr. balanced via XLR connectors
3 pr. single-ended via RCA connectors
1 dedicated iPod input via 30-pin connector

1 pr. preamp outputs via RCA connectors
1 pr. speaker outputs via gold-plated binding posts

Control inputs
1 RS-232 input via 9-pin D-subminiature connector
1 remote IR detector input via 3-conductor 3.5 mm connector
1 12 VDC trigger input via 2-conductor 3.5 mm connector

Control output
1 programmable 12 VDC trigger output (30 mA maximum current) via 2-conductor 3.5 mm connector

Input impedance
Balanced: 95 kΩ
Single-ended: 47.5 kΩ

Frequency response
20 Hz to 20 kHz +0, -0.08 dB

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Signal-to-noise ratio
>89 dB, wideband, unweighted, at maximum gain, referred to full power output
>96 dB, “A”-weighted

32.0 dB

Input sensitivity
Single-ended or balanced: 1.18 V RMS

Total harmonic distortion
<0.025% at 1 kHz, at 275 W, 8 Ω load
<0.20% at 20 kHz, at 275 W, 8 Ω load

Output power
275 W RMS per channel at 8 Ω
550 W RMS per channel at 4 Ω

Output voltage
133 V peak to peak
47 V RMS

Output current
20 A peak

Slew rate
80 V/μs

Output impedance

Damping factor
>110 at 20 Hz, referred to 8 Ω
>75, 20 Hz to 20 kHz, referred to 8 Ω

Power consumption
Standby: 1 W
High-current standby: 40 W
Idle: 90 W
Maximum: 1800 W

Heat output
Standby: 3.4 BTU/hr
High-current standby: 140 BTU/hr
Idle: 310 BTU/hr
Maximum: 2400 BTU/hr

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Specifications for preamp only:

6.3 dB (single-ended)

Volume control
Current-mode, 12-bit, discrete R-2R ladder

Input overload
Balanced: 12 V RMS
Single-ended: 6 V RMS

Output overload
8 V RMS (single-ended)

Frequency response
20 Hz to 20 kHz +0, -0.05 dB

Total harmonic distortion
<0.009%, 20 Hz to 20 kHz, at 2 V RMS

Signal-to-noise ratio
>87 dB, wideband, unweighted, at maximum gain, referred to 2 V RMS
>94 dB, “A”-weighted

17.26 in W x 5.84 in H x 17.70 in D
438 mm W x 148 mm H x 450 mm D

Unit only: 64 lb [29.0 kg]
As shipped: 76 lb [34.4 kg]

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