Усилители мощности стерео — Krell DUO 300 XD

The DUO 300 XD is a stereo amplifier without preamp section, built by Krell Industries of the USA, and belongs to the XD generation of its Duo stereo amps. It is a fully analog design that runs in Class A under Krell's iBias system, which lets the output stage stay in that operating class while producing much less heat and drawing less power than a conventional fixed-bias Class A amplifier would.

Key specs that matter

Rated output is 300 W RMS per channel into 8 ohm and 540 W RMS per channel into 4 ohm. Gain is 26.2 dB. Frequency response is 20 Hz to 20 kHz within +0 and -0.13 dB, and 0.5 Hz to 100 kHz within +0 and -3 dB. THD is below 0.045% at 1 kHz and 400 W into 8 ohm, and below 0.17% at 20 kHz at the same level. Signal-to-noise ratio exceeds 98 dB wideband unweighted and 116 dB A-weighted. Output voltage reaches 138 V peak-to-peak or 49 V RMS, peak output current is 16 A and slew rate is 40 V per microsecond. Output impedance stays below 0.007 ohm from 20 Hz to 20 kHz, giving a damping factor above 1140 referred to 8 ohm.

Engineering and use context

The XD label marks the step in which Krell lowered output impedance below its earlier norms, a technique found while developing the K-300i integrated amplifier and then carried over to the stand-alone power amps. Connection is by a pair of RCA connectors plus a pair of XLR connectors, with input impedance of 100 kilohm on RCA and 200 kilohm on XLR. Each channel has dual pairs of binding posts, so bi-wiring needs no jumpers at the speaker end. The circuit carries no digital section of any kind, keeping the whole signal path in the analog domain from input to output. Power draw is 180 W at idle and up to 1600 W at maximum. The chassis measures 434 mm wide, 194 mm high and 536 mm deep. The amplifier weighs 31.8 kg on its own and 36.4 kg packed for shipping, which is worth allowing for when choosing a rack shelf.

Pairing

Given its reserve into low impedances and high peak current, the DUO 300 XD is aimed at low-impedance and low-efficiency loudspeakers that a smaller amplifier would struggle with. The balanced XLR inputs suit a preamplifier that has XLR outputs, particularly across long runs, while the RCA pair covers a single-ended source or preamp. The idle draw means the amplifier should sit on a dedicated mains outlet with space around it for airflow.

Alternatives

The Krell DUO 175 XD is the lower-powered stereo model of this series, offering 175 W RMS into 8 ohm and 350 W RMS into 4 ohm.