Western Electric Type 91E Integrated Amplifier Lab Report

Lab Report

Western Electric's own spec for the 91E – 2x14W, 16W and 20W/8ohm at 3%, 5% and 10% THD, respectively – is higher than typically achieved with 300B/SETs but its 'SCS' circuit arguably departs from purist principles, influencing not only power. The 2.1-2.8ohm output impedance of the 8ohm transformer tap will modify the amp/speaker frequency response in line with the varying load of the latter even though, into a non-reactive 8ohm, the 91E offers a response that's flat to –1dB from 14Hz-21.4kHz before rolling away to 100kHz/–16dB. In practice, power output was a shade lower than specified into 8ohm at 4W/1% THD, 10W/3% and 11W/5% but bang-on target at 5W/1% THD, 14W/3% and 17W/5%. Under dynamic conditions this translates to 12.3W and 15.3W into 8 and 4ohm loads but just 3.2W and 1.5W into low 2 and 1ohm loads [see Graph 1]. The trend of THD vs. output level is clear from Graph 1 as is the increase at low and high frequency extremes – from 0.45%/1kHz to 1.0%/20Hz and 2.8%/20kHz (all re. 0dBW) – in Graph 2, below. Finally, the A-wtd S/N ratio is a creditable 83.8dB (re. 0dBW).

WE's resistor-ladder volume control operates over a ~100dB range where its 0.5dB steps are most accurate from volume '90' down to '40', but are closer to ±0.6dB from '30' to '10', and less reliable below '09'. The BT input, meanwhile, offers a 94.8dB A-wtd S/N (re. 0dBV via the line out) and linearity good to ±0.1dB over 60dB and ±0.7dB over 90dB (data is muted at 96dB/16-bits). Distortion is a minimum of 0.003-0.005% but lossy compression kicks in at just –50dB above 14kHz while the response (measured using a multitone to saturate the aptX bit pool) rolls away by 5dB from 100Hz to 1kHz and 9dB from 1kHz to 20kHz. PM


Dynamic output versus THD into 8ohm (black trace; continuous, grey), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 2.0A


Distortion vs. freq. (5Hz-40kHz at 0.1W/8ohm, black; 20Hz-40kHz/1W, pink; 40Hz-20kHz/5W, red)

Power output (<5% THD, 8/4ohm) 11.3W / 16.9W
Dynamic power (<5% THD, 8/4/2/1ohm) 12.3W / 15.3W / 3.2W / 1.5W
Output imp. (20Hz–20kHz/100kHz) 2.14-2.78ohm / 6.9ohm
Freq. response (20Hz–20kHz/100kHz) –0.4dB to –0.88dB/–16.0dB
Input sensitivity (for 0dBW/12W) 87mV / 302mV
A-wtd S/N ratio (re. 0dBW/12W) 83.8dB / 94.6dB
Distortion (20Hz-20kHz, 0.1-1W/8ohm) 0.15-0.7% / 0.43-2.8%
Power consumption (Idle/Rated o/p) 145W / 140W
Dimensions (WHD) / Weight 480x280x380mm / 22.2kg
Price £16,998 (£18,500 in nickel)

Western Electric
Rossville, GA, USA
Supplied by: Absolute Sounds Ltd, UK
0208 971 3909