Усилители мощности моно — Boulder 1151

The 1151 is a single-channel amplifier belonging to the 1100 Series from Boulder Amplifiers, designed, machined and assembled at the company's own facility in Louisville, Colorado. Boulder built it to deliver high current into difficult loudspeakers from a chassis that one person can install and that fits conventional equipment racks. Its width and depth match the 1110 Preamplifier and the 1161 Stereo Amplifier, and it runs from a standard power cord.

Key specs that matter

Continuous output is 250 W into 8, 4 and 2 ohms alike. Peak output is 350 W into 8 ohms, 600 W into 4 ohms and 750 W into 2 ohms. At 250 W distortion is 0.002%, rising to 0.01% at 20 kHz into 8 or 4 ohms, and into 2 ohms the figures are 0.003% and 0.02%. Signal to noise is -108 dB over 10 to 80 kHz, and equivalent input noise is 2.2 microvolts. Response is flat within 0.04 dB from 20 Hz to 20 kHz and falls 3 dB at 0.015 Hz and 150 kHz. Voltage gain is 26 dB. Input impedance is 200 kOhm balanced or 100 kOhm unbalanced, and common mode rejection reaches 90 dB at 60 Hz and 65 dB at 10 kHz. Each amplifier weighs 24.5 kg, and power draw is 10 W in standby, 60 W at idle and 800 W at full output.

Engineering and use context

Boulder biases the output section with its Class-A Smart Current scheme. An analog circuit monitors the current the speaker draws and adjusts bias continuously as the load impedance changes with frequency, which removes crossover distortion at the polarity transition without the heat of a fixed Class A design. Each chassis holds 40 output transistors and 12 supply capacitors, using many smaller capacitors instead of a few large ones, and a pair of 1151 amplifiers has more output devices than one 1162 stereo amplifier. The signal path has two stages, with the first providing most of the voltage gain so the output section can concentrate on current delivery. Protection circuitry shuts the output down at once if speaker cables short or a system fault appears. Heat sinks are machined from solid aluminium billet, the feet use constrained layer damping, and the front panel reproduces a topographical map of Flagstaff Mountain near Boulder.

Pairing

The input is a 3-pin balanced XLR, so a balanced preamplifier such as the Boulder 1110 is the obvious source. Two sets of 6 mm wingscrew terminals accept bi-wired loudspeakers, and mains versions exist for 100, 110-120 and 220-240 V supplies.

Alternatives

The Boulder 851 Mono Power Amp is the smaller 800 Series monoblock, built around its own Smart Current output stage.