Audio Research I/50 Integrated Amplifier Lab Report

Lab Report

This is not only a high performance tube amp, but one very shrewdly designed for the 'modern era' where 2V line outputs are the norm. It's perfectly typical for integrated amps to have anywhere from 35dB to 45dB overall gain – an excessive value where the volume knob hardly gets off its rest position before the amp is slammed into clipping. Not so here, for the I/50's gain is just +19.5dB (balanced in) at the maximum '45' volume setting. This is perfectly adequate, albeit more typical of a power amp than integrated amp, requiring 2150mV input for the rated 50W/8ohm output. Hand-in-hand with this are extremely low levels of noise – just –78dBV (0.13mV) – and a very wide 92.8dB A-wtd S/N ratio. There are plenty of well-respected transistor amps that cannot match this!

But this is a 6550-based tube amp, not a solid-state bruiser, and the other performance figures reflect this (6550 beam tetrodes are often swapped out for KT88s, but I wouldn't recommend it here). Power meets ARC's 50W specification at 2x58W and 2x55W into 8 and 4ohm loads via 8 and 4ohm taps, respectively. There's a hint of headroom under dynamic conditions where 68W, 63W, 66W and 66W is achievable into 8ohm/8ohm tap, 4ohm/4ohm tap, 2ohm/4ohm tap and 1ohm/4ohm tap [see Graph 1]. The I/50's output impedance increases markedly from <1ohm at bass/midrange freqs to 6ohm/20kHz so there's a progressive treble roll-off with speakers that exhibit a declining HF load (–2.9dB/20kHz into 8ohm and 4ohm but –4.8dB/20kHz into 2ohm). Distortion, too, increases modestly with level from 0.15%/1W to 0.5%/10W and 0.9%/50W, and with frequency to 3.2%/20kHz/10W [see Graph 2, below]. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Maximum current is 8.1A


Distortion versus frequency at 1W/8ohm (black, 5Hz-40kHz) and 10W (red, 20Hz-20kHz)

Power output (<1% THD, 8/4ohm) 58W / 55W
Dynamic power (2% THD, 8/4/2/1ohm) 68W / 63W / 66W / 66W
Output impedance (20Hz–20kHz) 0.85–6.0ohm (8.6ohm/38kHz)
Freq. response (20Hz–20kHz/100kHz) –0.5dB to –2.9dB / –20.1dB
Input sensitivity (for 0dBW/50W) 300mV / 2150mV
A-wtd S/N ratio (re. 0dBW/50W) 92.8dB / 109.8dB
Distortion (20Hz-20kHz, 10W) 0.39–3.2%
Power consumption (Idle/Rated o/p) 160W / 290W
Dimensions (WHD) / Weight 420x225x350mm / 18.1kg
Price £5198

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