BAT VK-3500 Integrated Amplifier Lab Report

Lab Report

So-called hybrid amplifiers – combining a triode tube line/preamp stage with a bipolar/FET power amp stage – can either combine the 'colour' of tubes with the grunt of a solid-state output, or... not. Copland's CSA150 [HFN Jun '21] and PS Audio's BHK Signature [HFN Jul '16] showed us that the inclusion of a high voltage tube line stage needn't translate into higher distortion at the output, and Musical Fidelity's use of Trivistor tubes in various products typically delivered vanishingly low THD. BAT's VK-3500 is rather different because its technical 'fingerprint' is a true amalgam of low-feedback tube/transistor thinking. Power output is generous at 2x170W/8ohm and 2x275W/4ohm, increasing to 220W, 425W, 390W and 215W into 8, 4, 2 and 1ohm loads under dynamic conditions, but distortion is higher at lower power (0.18%/1W to 0.08%/100W) and into lower impedances [see Graph 1, below]. This same decreasing distortion profile remains consistent right across the audioband [see Graph 2, below] and it's this feature that, subjectively, may prove a boon.

Meanwhile, the 0.22-0.25ohm output impedance is high for a transistor amp and though still lower than might be expected from a tube output stage it will still have some impact on frequency response, depending on your choice of speaker. Into a 'flat' 8ohm load the HF response rolls away above 10kHz, reaching –0.25dB/20kHz and –3.6dB/100kHz while achieving –3dB/4Hz in the sub-bass. Overall gain (balanced in) is fairly high at +43dB and the A-wtd S/N slightly below average at 79dB (re. 0dBW), the latter a product of both LF hum and HF white noise. Stereo separation is held to at least 70dB while the fine volume control maintains an impressive 0.08dB channel balance. PM


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max current is 14.7A


Distortion vs. frequency at 1W/8ohm (black, 5Hz-40kHz), 10W (blue, 20Hz-20kHz) and 100W (red)

Power output (<1% THD, 8/4ohm) 170W / 275W
Dynamic power (<1% THD, 8/4/2/1ohm) 220W / 425W / 390W / 215W
Output impedance (20Hz–20kHz) 0.215–0.235ohm
Freq. response (20Hz–20kHz/100kHz) –0.1dB to –0.25dB / –3.6dB
Input sensitivity (for 0dBW/150W) 19mV / 245mV
A-wtd S/N ratio (re. 0dBW/150W) 79.1dB / 100.9dB
Distortion (20Hz-20kHz, 10W) 0.095–0.12%
Power consumption (Idle/Rated o/p) 77W / 570W (40W standby)
Dimensions (WHD) / Weight 483x146x394mm / 23kg
Price £12,995

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