Audio Research REF160M mono power amplifier Lab Report

This is not ARC's first outing with KT150 tubes, nor the first to incorporate auto-biasing, but it is the first Reference series model to utilise both [see The Family Tree sidebar]. Its 140W rating is met into 8 and 4ohm with 165W being delivered at up to 1% THD via the 8ohm and 4ohm taps. This improves very slightly under dynamic conditions to 170W/8ohm and 175W/4ohm with 200W/2ohm (<2% THD) and 165W/1ohm (<3% THD) all in the REF160M's 'Ultralinear' configuration [see Graph 1]. In 'Triode' mode the output falls to 82W/8ohm and 85W/4ohm with a very marginal reduction in distortion at very high frequencies [see black vs. green trace, Graph 2]. The meter is decorative only – 1W/8ohm (8ohm tap) reads 0.015W, 10W reads 0.15W and 100W reads 1.5W on the 'Ultralinear' scale.


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 12.9A


Distortion vs. frequency (20Hz-20kHz, 10W, red; 5Hz-40kHz, 1W Ultralinear, green; Triode, black)

The 'shaped' frequency response with its mild +0.1dB bass shelf from 300Hz down to 10Hz allied to a gentle mid/presence roll-off of –0.2dB/5kHz to –0.7dB/20kHz (and –7.1dB/100kHz) is a mildly exaggerated version of that offered by the REF150SE and GS150 as is the magnification of the trend with reducing load impedance (–1.3dB/20kHz into 4ohm and –2.3dB/20kHz into 2ohm). The 0.6-1.5ohm output impedance (20Hz-20kHz) is also shared between all three models. Distortion increases gently with output level from 0.035%/1W to 0.11%/10W and 0.5%/100W (all 1kHz/8ohm). Versus frequency, the minimum is at 100Hz (0.06% at 10W), increasing to 0.19%/20kHz. Noise is very low, extremely so for a substantial tube amp and some 13dB better than the GS150 at –83dBV (unweighted). The A-wtd S/N ratio is correspondingly wide and up with the quietest solid-state amplifiers at 101dB (re. 0dBW). PM

Power output (<1% THD, 8/4ohm): 165W / 165W
Dynamic power (<1% THD, 8/4/2/1ohm): 170W / 175W / 200W / 165W
Output impedance (20Hz–20kHz): 0.69–1.51ohm
Freq. resp. (20Hz–20kHz/100kHz): +0.1dB to –0.7dB/–7.1dB
Input sensitivity (for 0dBW/140W): 179mV / 2105mV (balanced)
A-wtd S/N ratio (re. 0dBW/140W): 100.5dB / 122.0dB
Distortion (20Hz-20kHz, 10W/8ohm): 0.06–0.19%
Power consumption (Idle/Rated o/p): 220W / 380W
Dimensions (WHD) / Weight: 438x254x457mm / 25.5kg
Price: £28,998 (per pair)

Audio Research Corp.
Minnesota, USA
Supplied by: Absolute Sounds Ltd.
0208 971 3909