Усилители мощности моно — Boulder 851

The Boulder 851 is a single-channel power amplifier in the 800 Series from Boulder Amplifiers. It takes the 861 Stereo Power Amplifier into a dedicated monoblock format, meaning stereo playback calls for a pair. Development had two constraints - the chassis had to share the footprint of the 812 DAC preamplifier, and it had to carry the Smart Current bias scheme. This makes the 851 the smallest Boulder power amplifier with Smart Current, and the only Class A amplifier in the 800 Series.

Key specs that matter

Continuous power is 100 W into 8 ohms and 200 W into 4 ohms. Peak ratings are 150 W at 8 ohms, 250 W at 4 ohms and 350 W at 2 ohms. THD is listed at 0.002%. Maximum analog gain is 26 dB. One pair of balanced 3-pin XLR inputs presents an impedance of 100 kohm. Mains versions are offered for 100 V, 120 V and 240 V at 50 to 60 Hz, and maximum power consumption is 550 W. Each chassis measures 304.8 x 304.8 x 88.9 mm and weighs about 10 kg.

Engineering and use context

Boulder says that dedicating the whole chassis to one channel simplifies the signal path compared with the stereo 861. The Smart Current Output stage is a first for the 800 Series, and the design uses numerous output devices to deliver more current than other designs of similar rating. The amplifier was designed, tested and assembled in the Boulder factory of about 2,140 m2 in Louisville, Colorado, a 10 minute drive from where the company was founded in Boulder, and all circuit boards and metalwork for it are made there. Protection is extensive. On a short circuit, a current limiter silences the output, and since the 851 is DC-coupled, a DC detection circuit also mutes the outputs to keep damage away from the speakers. A thermal circuit mutes the amplifier when the heatsinks reach 70 degrees C. Firmware can be updated by online download or through installation from a USB drive, according to Boulder. Speaker cables attach to traditional 6 mm thumbscrew binding posts.

Pairing

The matching footprint lets the 851 sit beside the 812 DAC preamplifier, which Boulder presents as a home audio system when combined with a pair of 851 amplifiers. The 808 Phono Preamplifier shares the same footprint and adds a turntable input to the 800 Series setup.

Alternatives

The Boulder 1151 is the single-chassis mono amplifier of the 1100 Series, rated at 350 W peak into 8 ohms and 600 W peak into 4 ohms.