Audio Research REF160S Tube Power Amplifier Lab Report

Lab Report

With differences between the original REF160M [HFN Aug '18] and this stereo version boiling down to necessary changes in PCB layout, one less filter capacitor and positioning of two fans under the chassis, comparisons are intriguing. Is the REF160S really equivalent to two REF160Ms? Let's start by looking at power output: both amps have the same 140W rating and this is met into 8 and 4ohm with 2x169W (160S) and 165W (160M) being delivered at up to 1% THD via the 8ohm and 4ohm taps. This improves very slightly under dynamic conditions to 180W into 8/4ohm with 215W/2ohm (<2% THD) and 185W/1ohm (<3% THD) all in the REF160S's 'Ultralinear' configuration [see Graph 1, below] and just a few watts ahead of the REF160M. In 'Triode' mode the output from both 160S and 160M falls to 82W/8ohm and 85W/4ohm with a very marginal reduction in distortion at the frequency extremes [black vs. green trace, Graph 2 below].

The 'shaped' frequency response with its mild +0.1dB bass boost from 300Hz down to 10Hz allied to a gentle mid/presence roll-off of –0.2dB/5kHz is retained in the REF160S but the HF roll-off is less exaggerated. Here it is just –0.25dB/20kHz down to –4.0dB/100kHz, as opposed to –0.7dB/20kHz and –7.1dB/100kHz in the REF160M (Ultralinear mode, 1W/8ohm), although the 0.7-1.5ohm output impedance (20Hz-20kHz) is unchanged via the 8ohm tap. Once again, distortion increases gently with output level from 0.05%/1W to 0.15%/10W and 0.6%/100W (all 1kHz/8ohm). Versus frequency, the minimum is at 40Hz (0.05% at 10W), increasing to 0.22%/20kHz. Noise is very low, but not as low as in the REF160M which achieved an A-wtd S/N ratio of 100.5dB (re. 0dBW). For the REF160S, the figure is 94dB. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 13.6A


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

Power output (<1% THD, 8/4ohm) 169W / 170W
Dynamic power (<5% THD, 8/4/2/1ohm) 180W / 181W / 215W / 185W
Output impedance (20Hz–20kHz) 0.687–1.48ohm
Freq. response (20Hz–20kHz/100kHz) +0.1dB to –0.25dB/–4.0dB
Input sensitivity (for 0dBW/140W) 179mV / 2105mV (balanced)
A-wtd S/N ratio (re. 0dBW/140W) 93.6dB / 115.1dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.06–0.19%
Power consumption (Idle/Rated o/p) 420W / 740W
Dimensions (WHD) / Weight 483x260x546mm / 45kg
Price £19,998

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