Усилители мощности стерео — Boulder 1163

The Boulder 1163 belongs to the 1100 Series from Boulder Amplifiers, as a stereo amplifier aimed at listeners with smaller living spaces or more efficient systems. It follows the 1161, and although the exterior looks similar, every board of the predecessor was modified and improved. The concept carries what Boulder learned from the 1151 Mono Power Amplifier into a single stereo chassis that ships in a carton and fits a conventional audio rack. Boulder describes it as the most compact stereo amplifier in the 1100 Series with the Class A Smart Current Output Stage.

Key specs that matter

Continuous output is 150 W per channel into 8 ohms. Peak power is 200 W at 8 ohms, 325 W at 4 ohms and 550 W at 2 ohms. The -3 dB points are 0.015 Hz and 150 kHz, and between 20 Hz and 20 kHz the response stays within +0.00 and -0.04 dB. Voltage gain is 26 dB, and equivalent input noise across a 20 kHz bandwidth is 2.2 uV. Input impedance is 50 kohm balanced and 25 kohm unbalanced. The amplifier weighs 24.5 kg, or 29 kg in its shipping carton, and mains versions cover 100, 120 and 240 V at 50 to 60 Hz. It shares features with the larger 1162 but occupies the footprint of the 1110 Preamplifier and works from a standard mains cord.

Engineering and use context

Two stages make up the circuit, as in all 1100 Series power amplifiers. The first, built on the Boulder 985 gain stage, provides most of the voltage gain, leaving the output stage of 40 transistors to deliver current to the speaker. The supply uses 12 capacitors, and the output section relies on many smaller filter capacitors in place of fewer large units. The Smart Current stage monitors the current drawn by the speaker and adjusts the bias through analog circuitry, which Boulder says removes crossover distortion without the heat of traditional Class A. A revised automatic bias circuit needs no manual calibration, and new protection shuts the output down at once on a fault or a shorted speaker cable. Every panel is machined from solid aluminum, the top panel is damped during assembly, and the transformer is potted, encased and damped. The front panel carries a topographic map of Flagstaff Mountain. Firmware updates arrive by online download or USB.

Pairing

Inputs are balanced 3-pin XLR, and two sets of 6 mm wingscrews per channel accept bi-wired loudspeakers. The 1110 Preamplifier and 1108 Phono Preamplifier complete an 1100 Series system.

Alternatives

Boulder also builds the 1162, a larger two-channel amplifier from the 1100 Series.