Krell

Power Supplies
Housed in a separate chassis, the power supply makes use of extensive electrical and magnetic shielding to keep radiated interference out of critical amplifier circuits. Internal high current line conditioning circuitry filters RF noise on the AC mains, as well as compensating for asymmetric power waveforms and DC on the mains. A dedicated 165 VA toroidal transformer with six independent secondary windings powers the amplifier's low level stages, gain stages, and control circuitry. Power for the high current regulators and amplifier output stages comes from two massive 2500 VA toroidal transformers. These in turn drive eight 35-amp bridge rectifiers and 120,000 microfarads of filter capacitance. High reliability connectors with 56 machined, gold plated, 20-amp contacts transmit these tremendous power reserves to the regulators.

Power Supply Regulation For Absolute Voltage Stability
The rails powering the amplifier's low level and gain stages are regulated twice for total immunity from fluctuations in the AC mains and virtually noise-free output. All the regulators use current-mode circuitry for wide bandwidth, low output impedance, and complete immunity to varying load conditions. The high-current regulators powering the amplifier output stages use fully complementary gain stages and output drivers. The resulting wide bandwidth and low output impedance of the Evolution One surpasses even the stringent demands of the amplifier output stages.
The driver and output stages in the high current regulators use 14 pairs of the same robust, high performance power transistors used in the amplifier output stages. All the regulators are located in the amplifier chassis to provide ultra low impedance supply rails for the audio circuitry.

Evolution Krell CAST
By employing radical current mirror circuitry, the Evolution components elevate the CAST technology to another level. This advanced use of the technology increases the linearity, transient speed, and bandwidth of the Evolution components while reducing the distortion by an order of magnitude. Together, CAST and Krell Current Mode technologies unify separate Krell components into a single global circuit. Krell Current Mode technology enjoys bandwidth increases up to an order of magnitude greater than their voltage based counterparts. This dramatic increase in circuit bandwidth delivers near perfection in the audible band that typically suffers from phase distortions in voltage circuits.

Circuitry Highlights
Audio signal voltages are converted to currents at the amplifier input, and the audio signal remains in the current domain throughout the entire amplifier until the output stages. All signal gain is realized in the current domain using proprietary multiple-output current mirrors with extraordinary open loop linearity. The current mirrors in the final gain stages use 36 pairs of high voltage, high speed transistors. Originally developed for demanding, high bandwidth video circuits, these transistors help yield gain stages with superb accuracy and very low distortion. The signal path is fully complementary and fully balanced from input to output. The driver and output stages use 28 pairs of 150 Volt, 14 Amp, 50 megahertz power transistors mounted on Krell-designed high efficiency heat sinks.
All transistors operate in Class A mode. Independent complementary pre-driver and driver stages for the positive and negative output transistors make the output stages extremely fast and linear. The output stage develops 450 Watts into an 8 Ohm load, 900 Watts into 4 Ohms, and 1800 Watts into 2 Ohms. This unique circuit is impervious to low-impedance or reactive loads; the Evolution One amplifier simply drives any loudspeaker with absolute confidence, achieving the very best possible sonic results.

Impedance Advantage
The output impedance of the final gain stages is one hundredth that of the final gain stage in most power amplifiers. This provides extremely wide bandwidth and very high current capability. The amplifier does not employ global negative feedback—the final gain stages use only 8 dB of local, nested negative feedback. This is one five hundredth the amount used in most solid-state power amplifiers. The result is an extraordinarily open, liquid, effortless sound.

Evolution Bias Control Systems
The new Evolution Bias system features 12 individual bias levels for optimum performance and efficiency. Evolution Bias constantly compares the audio signal at the input stage with impedance at the output stage, and adjusts the bias current accordingly. In addition, a proprietary bias monitor continuously measures and adjusts the output stage bias, eliminating the need for future adjustment or calibration.

Advanced Microprocessor Control
If the DC level at the amplifier inputs exceeds a safe level, the microprocessor control automatically switches in DC blocking capacitors to prevent damage to the input stages or the loudspeakers. The microprocessor control measures the load impedance in real time to optimize the performance of the amplifier and power supply or, in the case of a short circuit, to shut the amplifier off. It monitors the regulator output voltages, the symmetry between the two halves of the balanced output stages, and it monitors the operating temperatures of the three main heat sinks. If any of the heat sinks become too hot, the microprocessor control adjusts the operating parameters of the amplifier and power supply to help the circuitry run cooler. If the temperature of any of the heat sinks becomes unsafe, the microprocessor control shuts the amplifier off until it cools down. In the event of a major protection fault the microprocessor flashes a diagnostic code on the power/stand-by LED. The RMS output voltage and current signals used by the microprocessor are also used by the power meter, on the amplifier front panel, to display accurate power measurements.

Frequency response
20 Hz to 20 kHz+/-0.05 dB
0.6 Hz to 220 kHz+0, -3 dB
Signal-to-noise ratio
118 dB, "A"-weighted
Gain
25.8 dB
Total harmonic distortion
<0.01% at 1 kHz, at 450 W, 8 Ohms
<0.1% at 20 kHz, at 450 W, 8 Ohms
Input impedance
Balanced: 100 kOhms
CAST: 50 Ohms
Input sensitivity
Balanced: 3.08 V RMS
CAST: 3.08 mA RMS
Output power
450 W RMS at 8 Ohms
900 W RMS at 4 Ohms
1800 W RMS at 2 Ohms
Output voltage
170 V peak-to-peak
60 V RMS
Output current
57 A peak
Slew rate
100 V/µs
Power consumption
Standby: 225 W
Idle: 300 W
Inputs
1 balanced via XLR connector
1 CAST via 4-pin bayonet connector
Outputs
1 pair Krell binding posts
Dimensions
Amplifier chassis:

15.8 in. W x 6.2 in. H x 21.5 in. D
40 cm W x 15.8 cm H x 54.7 cm D
Power supply chassis:
15.8 in. W x 6.4 in. H x 20.5 in. D
40 cm W x 16.1 cm H x 52.2 cm D
Amplifier channel:
15.8 in. W x 12.5 in. H x 21.5 in. D
40 cm W x 31.6 cm H x 54.7 cm D
Weight
Amplifierchassis:

Shipped: 70 lbs., 31.7 kg
Unit Only: 55 lbs., 24.9 kg
Power supply chassis:
Shipped: 110 lbs., 49.8 kg
Unit Only: 95 lbs., 43 kg

 

Hi Fi News

"Has Krell built the best ever amp system known to man with its Evolution Series?" Read More...

The Absolute Sound

"There is a level of excellence at which conventional words about quality and cost-effectiveness become meaningless. Like the very best cars, watches, and wines, and every other assault on the consumer state of the art that you can actually buy, price ceases to be an object. You choose because it is a personal passion—if not an obsession—and because you are lucky enough to be one of the handful of people who really can afford the very best.The Krell Evolution preamp and amplifier are cases in point."
Read More...

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