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

323west.lab1

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

323west.lab2

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)

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