Усилители мощности стерео — Krell DUO 175 XD

The Duo 175 XD is a Krell stereo power amplifier based on Class A iBias circuitry in XD form, with a direct-coupled signal path, current-domain gain stages and discrete components throughout. It is the smaller stereo model in the XD range and shares its chassis size with the Solo monoblocks.

Key specs that matter

Output is 175 W RMS per channel into 8 ohm and 350 W RMS into 4 ohm. Available voltage is 106 V peak to peak or 37 V RMS, and each channel can deliver 13 A of peak current. Gain is 26.2 dB, and 1.84 V RMS at either the RCA or the XLR input is enough for full rated output, with input impedance of 100 kohm single-ended and 200 kohm balanced. The response stays within 0.08 dB from 20 Hz to 20 kHz and extends from 0.5 Hz to 100 kHz at the 3 dB points. Distortion is below 0.03% at 1 kHz and 175 W into 8 ohm, and below 0.13% at 20 kHz at the same power. Signal to noise is better than 95 dB wideband unweighted and 115 dB A-weighted. Output impedance under 0.015 ohm from 20 Hz to 20 kHz gives a damping factor above 530 referred to 8 ohm, and slew rate is 40 V per microsecond.

Engineering and use context

Conventional Class A designs run a large fixed bias current all the time. The iBias circuit instead monitors the current going to the loudspeakers and continuously sets the bias to what the signal needs, so Class A operation is kept while idle losses remain moderate. Consumption is 1 W in standby, 73 W at idle and 1500 W at maximum, with heat output rising from 250 BTU per hour at idle to 5137 BTU per hour at full power. The chassis is 434 mm wide, 194 mm high and 536 mm deep and weighs 27.3 kg, or 31.8 kg in its shipping carton. Two RCA and two XLR inputs are provided, one of each per channel, along with two pairs of speaker terminals. The XD label marks the upgraded generation that followed Krell's first iBias amplifiers.

Pairing

The amplifier works with most preamplifiers on either balanced or single-ended cables, and the doubled output at half the impedance together with the very low output impedance suits loudspeakers with low or uneven impedance. Placement should allow airflow around the chassis given the heat produced at high output, and the high maximum draw is worth considering when several components share one mains outlet.

Alternatives

The Krell Duo 300 XD is the higher-powered two-channel model of the XD series, rated at 300 W per channel into 8 ohm and 540 W into 4 ohm.