Krell KMA-i800 800-Watt Mono Amplifier with iBias/XD/Sym-Max Tech (PAIR)

Description

KMA-i800 Mono Amplifier

PRICED AS A PAIR OF MONO AMPS

The KMA-i800 is a state-of-the-art 800 watt monaural
amplifier. It incorporates Krell’s most advanced circuit topologies and Krell’s
proprietary technologies iBias, XD, and Sym-Max. This gives the KMA-i800 a warm
enveloping three-dimensional sound with unparalleled detail, along with the
rock-solid bottom end and effortlessness that Krell is known for.

Differential Output

The KMA-i800 is a differential output amplifier. This means
it contains two identical amplifiers operating out of phase to produce an
output signal twice as large as a single amplifier. The main advantage of this
configuration is cancelation of common-mode distortion and noise components.
The KMA-i800 also incorporates special compensation to maintain very low output
impedance at the low end of the frequency range. This produces high impact
extended bass that is felt as much as it is heard.

iBias

iBias enables the KMA-i800 to operate in Class A up to its
full rated power of 800 watts with absolute accuracy but without the heat
produced by a traditional Class A design. It does this by using a novel circuit
to unobtrusively monitor the current flowing through the output stage. This is
part of a closed-loop controller that makes sure this current never drops below
a preset level (Class A means that it never drops to zero). This is what makes
the amp both efficient and accurate.

The efficiency comes from the controller adjusting the bias
to maintain that low preset current level as the signal and speaker load changes.
Traditional Class A amplifiers set it for the maximum level all the time so
they’re always dissipating the maximum amount of heat. iBias is like having a
variable size Class A amplifier. If, for example, the signal and speaker are
only requiring 10 watts, it’s like having a 10 watt Class A amplifier, all the
way up to 800 watts in the case of the KMA-i800.

The accuracy also comes from maintaining that low preset
current level. It doesn’t matter what the signal is doing or how the speaker
impedance changes with frequency, by maintaining that preset current level the
amplifier is always operating in Class A. Other variable bias schemes monitor
the input or output signal to adjust the bias but that doesn’t take into
account varying speaker impedance. This means they will sometimes apply more
bias current than necessary or drop out of Class A operation.

XD

XD is a technique for lowering the amplifier’s output
impedance. This results in better control over the speaker drivers which
improves musical dynamics, depth, and dimensionality. It is very dependent on
maintaining thermal equilibrium in the output stage so that all the output
transistors are contributing equally to the signal output. The KMA-i800 uses a
massive aluminum device bar to mount the output transistors and also employs
special temperature compensation across the device bar to limit temperature variations.

Sym-Max

Sym-Max is short for “Symmetry Maximization.” The circuitry
in the KMA-i800 is differential, meaning that there is a positive half and a
negative half. The transistors in this circuitry are complimentary, meaning
opposite polarity but with equal characteristics. In practice they are not so
equal which means the circuit is operating asymmetrically. Sym-Max makes small
adjustments in the circuit parameters to remove this asymmetry. The result is
that 2nd order harmonic distortion is almost completely eliminated. This
dramatically opens up the sound stage with more detail and a better sense of
pacing, making for a more realistic experience.

Power

The heart of any power amplifier is the power supply. The
KMA-i800 has a massive power supply consisting of 5800VA of transformers and
188,000uF of filter capacitance. Delivering this power to the output circuit is
a combination of gold-plated circuit boards and silver-plated solid copper buss
bars with a very short physical path for extremely low impedance. This, along
with the audio circuitry enables the KMA-i800 to double its power from 800
watts into 8 ohms to 1600 watts into 4 ohms and even 3200 watts into 2 ohms. It
can drive 1 ohm speakers and will deliver a peak current of up to 56 amps.

Circuitry

The KMA-i800 uses Krell Current-Mode circuitry with advanced
current mirroring that is balanced, differential, and direct-coupled. Each
stage is independently tuned and matched to the previous stage for optimal
operation. The output stage consists of 16 pairs of 200 watt audio power
transistors and 8 pairs of audio driver transistors. This results in a
frequency response greater than 100kHz for effortless reproduction of the audio
band.

Control and Protection

The KMA-i800 is microprocessor controlled and has Ethernet
connectivity and a 12VDC trigger input for easy connection to a home
controller. The Ethernet connection allows access to the KMA-i800 web page for
status information and control. The KMA-i800 is protected against high DC on
the outputs, output short circuit conditions, and power brown outs. The
protection operation is conveniently indicated on the front panel status lights
and the web page.

Analog Inputs

1 balanced via XLR connector

1 single-ended via RCA connector

Outputs

2 pr. speaker outputs via gold-plated binding posts

Control inputs

1 Ethernet via RJ45

1 12 VDC trigger input via 2-conductor 3.5 mm connector

Input impedance

Balanced: 28 kΩ

Single-ended: 14 kΩ

Frequency response

20 Hz to 20 kHz +0, -0.13 dB

-3dB bandwidth 147kHz (measured at 50W into 8Ω)

Signal-to-noise ratio

>109 dBr, wideband, unweighted, referred to full power output

>120 dBr, “A”-weighted

Gain

26.5 dB

Input Sensitivity

3.8 V RMS

Total harmonic distortion

<0.010%, 1 kHz, 800W, 8Ω load

<0.035%, 20 kHz, 800W, 8Ω load

Output power

800W RMS at 8Ω

1600W RMS at 4Ω

Output voltage

245 V peak to peak

86 V RMS

Output current

56 A peak

Slew rate

35 V/μs

Output impedance

0.009 Ω, 20 Hz

0.018 Ω, 1 kHz

Damping factor

>800, 20 Hz referred to 8 Ω

>400, 1kHz referred to 8 Ω

Power consumption

Standby: 1 W

Idle: 260 W

Maximum: 4750 W (4Ω load)

Heat output

Idle: 890 BTU/hr

Maximum: 10,773 BTU/hr (4Ω load)

Dimensions

17.25 in W x 9.4 in H x 24 in D

438 mm W x 239 mm H x 610 mm D

Weight

Unit only: 145 lbs [66 kg]

As shipped: 180 lbs [82 kg]