BAT VK-80i Integrated Amplifier Lab Report

Lab Report

This is a bold attempt by BAT to offer a valid triode-based alternative to the more traditional 6550/KT90 tetrode-powered output stage favoured by many (valve-focused) amplifier brands. The 6C33C-B power triodes used in the VK-80i can match pairs of KT90s used in push-pull configuration for raw watts, particularly into low impedances, but there's a trade-off with distortion which increases steadily with output. The latter increases from an already high 0.65%/1W to 1.5%/10W and fractionally under 3% at 50W (all 1kHz/8ohm). Unlike the typical KT90-based design, distortion does not increase at high frequencies [see Graph 2, below] although there's no escaping the marked increased in bass distortion through, presumably, output transformer core saturation. Noise, too, is slightly higher than average, leading to an A-wtd S/N ratio of 78.5dB (re. 0dBW).

All this feeds into the maximum power output available from the VK-80i which amounts to 21W at 2% THD, 34W/2.5% and 53W at the rated 3% THD into 8ohm (all via the 'High' 6-8ohm tap). Into 4ohm loads via the 'Med' 4-6ohm tap this translates into 20W/2%, 37W/2.5% and 51W/3% THD, and into 2ohm via the 'Low' 3-4ohm tap at 16W/2%, 33W/2.5% and 46W/3%. There is significantly more juice available under dynamic conditions where the VK-80i achieves 97W, 102W and 105W into 8, 4 and 2ohm loads via the aforementioned taps at up to 3% THD [see Graph 1, below]. Into very low 1ohm loads this is limited to just 15W where the source impedance of the 'Low' tap is already twice this value at 2ohm. I discuss the impact of this high impedance on frequency response in our sidebar although the 'native' response is flat to within ±1dB from 13Hz-60kHz. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max current is 10.3A


Distortion vs. frequency at 1W/8ohm (black, 5Hz-40kHz), 10W (blue) and 30W (red, 20Hz-20kHz)

Power output (<3% THD, 8/4/2ohm) 53W / 51W / 46W
Dynamic power (<3% THD, 8/4/2/1ohm) 97W / 102W / 105W / 15W
Output imp. (20Hz–20kHz/100kHz) 1.99–2.06ohm / 2.83ohm
Freq. response (20Hz–20kHz/100kHz) +0.39dB to –0.14dB / –2.8dB
Input sensitivity (for 0dBW/55W) 204mV / 1513mV
A-wtd S/N ratio (re. 0dBW/55W) 78.5dB / 95.9dB
Distortion (20Hz-20kHz, 10W) 9.5%–1.0%
Power consumption (Idle/Rated o/p) 470W / 680W (1W standby)
Dimensions (WHD) / Weight 431x203x406mm / 20.4kg
Price £9995

Balanced Audio Technology Inc.
Wilmington DE, USA
Supplied by: Karma-AV Ltd, York
01423 358846