Усилители мощности стерео — Boulder 861

The 861 is a stereo amplifier belonging to Boulder's 800 Series and, according to the company, the most compact and lightest stereo power amplifier it makes. It was designed to share the exact footprint of the 812 DAC Preamplifier, so the two form a matched pair of separates. Boulder aimed it at smaller living spaces, at systems built around efficient loudspeakers and at owners who like the 866 Integrated but prefer separate components.

Key specs that matter

Continuous output is 50 W per channel into 8 ohms and 90 W into 4 ohms. Peak ratings are 75 W into 8 ohms, 110 W into 4 ohms and 200 W into 2 ohms. The single pair of inputs is balanced on 3-pin XLR, with 100 kOhm input impedance and 26 dB of gain. Distortion is 0.01% and equivalent input noise is 2.6 microvolts at 20 kHz. Response stays within 0.04 dB from 20 Hz to 20 kHz and reaches its -3 dB points at 0.015 Hz and 150 kHz. Maximum power consumption is 550 W, and mains versions exist for 100, 120 and 240 V. The chassis measures 305 x 305 x 89 mm and weighs 10 kg.

Engineering and use context

Every circuit board and piece of metalwork is produced in Boulder's factory of about 2,100 m2 in Louisville, Colorado, where assembly and testing also take place. The casework carries the same gently sloping heatsinks as the 866 and 812. Numerous output devices let the 861 supply more current than typical designs of similar rating. The amplifier is DC coupled, and a DC detection circuit mutes the outputs to protect the speakers. A current limiter mutes the output in the event of a short, and a thermal circuit mutes the amplifier once the case reaches 70 degrees Celsius. Boulder notes that its revised protection lets the 861 deliver more current at maximum output without risk to the electronics. Speaker cables attach to Boulder's own 6 mm thumbscrew binding posts. IP control and a networked HTML page are built in, and firmware for the control and housekeeping systems can be updated online or through a USB port. The amplifier ships in a smaller carton than earlier Boulder power amplifiers.

Pairing

The modest continuous rating points to loudspeakers of reasonable efficiency and room sizes around 20 m2 rather than large, power-hungry designs. The 812 DAC Preamplifier is the intended partner, and when both units sit on the same network the 861 can be programmed to switch on in sequence with it.

Alternatives

The Boulder 1162 Stereo Power Amplifier from the 1100 Series is a far larger and heavier two-channel design.