Усилители мощности моно — Krell KMA I800

The KMA-i800 is a mono power amplifier from Krell, the American maker based in Connecticut. Krell describes it as a Class A design built around three of its own circuit technologies - iBias, XD and Sym-Max. The US price is USD 73,000 per pair.

Key specs that matter

Rated power is 800 W into 8 ohm, doubling to 1600 W into 4 ohm and again to 3200 W into 2 ohm. Maximum output voltage is 245 V peak to peak, or 86 V RMS, with 56 A of peak output current. THD is 0.010 % at 1 kHz and 0.035 % at 20 kHz, both at 800 W into 8 ohm. Slew rate is 35 V per microsecond. Input sensitivity is 3.8 V RMS, and input impedance is 28 kohm on the balanced input and 14 kohm on the single-ended input. The power supply holds 188,000 microfarads of filter capacitance. Each chassis measures 438 mm wide, 239 mm high and 610 mm deep and weighs 66 kg.

Engineering and use context

The iBias circuit monitors current into the speaker and adjusts bias in the output devices to match what the load actually demands. Krell states that this keeps the amplifier in Class A up to its full rated power without the heat of a conventional fixed-bias Class A design, so energy is not wasted when full power is not needed. XD lowers output impedance so the amplifier keeps tighter control of the drivers. Sym-Max, short for Symmetry Maximisation, applies differential circuitry that treats the positive and negative signal halves symmetrically. The signal path follows Krell Current-Mode practice, with a balanced, differential and direct-coupled layout and current mirroring between independently tuned stages. Circuit boards are gold-plated, and silver-plated copper bus bars carry supply current to keep impedance low. A microprocessor handles control, with an Ethernet port that opens a web page for status and control, and a 12 V DC trigger input for switching with the rest of a system. Protection covers DC at the output, short circuits and brownouts.

Pairing

A line stage with balanced XLR outputs is the natural feed, and its input sensitivity matches the output range of typical line stages. Its current capacity into very low impedances means low-impedance speakers with difficult loads are within the rated range. The trigger lets the pair power up together with a Krell preamplifier or a processor in a home cinema.

Alternatives

The Krell Solo 575 is a smaller iBias Class A mono power amplifier rated at 575 W.