Pre/Power Amplifiers

Segmented across the 1110's +20dB to –80dB gain, Boulder's volume control is a precision instrument in its own right, accurate to within ±0.1dB over the top 40dB of its dynamic range (volume +0.0dB to –40.0dB), ±0.2dB over a 80dB range and ±0.5dB over the full 100dB range. Distortion is vanishingly low at 0.0001-0.0003% [20Hz-20kHz; black trace, Graph 2], maximum output more than sufficient at 17.8V from a 49ohm source and the A-wtd S/N ratio very wide at 102dB (re. 0dBV). The frequency response is equally flat and extended to within ±0.01dB from 1Hz-20kHz, falling to a mere –0.5dB/100kHz.

The performance of the partnering 1160 power amp is no less impressive in its unflappable linearity. While Boulder rates the 1160 rather ambiguously at '300W into 8, 4 and 2ohm' the real world figures are 2x550/8ohm and 2x950W/4ohm with sufficient PSU reserve to accommodate 668W, 1.25kW and 2.19kW under dynamic conditions into 8, 4 and 2ohm loads at <1% THD. Electronic protection limits the output to 750W/1ohm [see Graph 1, below]. Distortion is extremely low but decreases with increasing power output from 0.0013%/1W to 0.00065%/10W and 0.0003%/100W before reaching 0.00025% at the rated 300W/8ohm (all re. 1kHz). This trend is unaffected by signal frequency although there is a steady increase in THD from, say, 0.00065%/1kHz to 0.0074%/20kHz [all re. 10W/8ohm; see Graph 2, below]. In common with the 1110, the 1160 is designed to offer a flat and extended response (±0.5dB, 1Hz-55kHz) from a low 0.005-0.009ohm source impedance (20Hz-20kHz) with very low noise – the A-wtd S/N ratio is 99.5dB (re. 0dBW). Both preamp and power amp are masterpieces of rugged engineering. PM